,transcriber ,note    ,text emphasis    
denoted as ,italics4          ,,the     
,international ,scientific ,series      
,,vol4 ,,xxxv4    ,frontispiece4        
,illustration    ,sections of ,igneous  
,rocks1 illustrating the passage from   
the glassy to  the crystalline          
structure4      #a4 ,vitreous ,rock4 #b4
 ,semi-,vitreous ,rock4 #c4 ,vitreous   
,rock with       ,sphrulites4 #d4 ,rock 
with ,crypto-crystalline ,base4 #e4     
,rock with       ,micro-crystalline     
,base4 #f4 ,rock of ,granite ,structure 
built up       entirely of ,crystals4   
,see pp4 #fc-fh4                        
,,volcanoes                       ,,what
 ,,they ,,are and ,,what ,,they ,,teach 
,,by                             ,,john 
,w4 ,,judd1 ,f4,r4,s4                   
,,professor ,,of ,,geology ,,in ,,the   
,,royal ,,school ,,of ,,mines           
,,with #if ,,illustrations              
,,sixth ,,edition                       
,,london                    ,,kegan     
,,paul1 ,,trench1 ,,tr,,bner  ,,co4     

,ltd4                     ,,paternoster 
,,house1 ,,charing ,,cross ,,road       
#aijc      7,the rights of translation  
and of reproduction are reserved47      
,,preface4      ,in preparing this work1
 ,i have aimed at carrying out a design 
suggested  to me by the late ,mr4       
,poulett ,scrope1 the accomplishment of 
which has  been unfortunately delayed1  
longer than ,i could have wished1 by    
many  pressing duties4    ,mr4 ,scrope's
 well-known works1 ',volcanoes' and     
',the ,geology and ,extinct  ,volcanoes 
of ,central ,france'--which passed      
through several editions  in this       
country1 and have been translated into  
the principal ,european                 
languages--embody the results of much   
careful observation and acute  reasoning
 upon the questions which the author    
made the study of his  life4 ,in the    
first of these works the phenomena of   
volcanic activity  are described1 and   
its causes discussed2 in the second it  
is shown that  much insight concerning  

these problems may be obtained by a     
study of  the ruined and denuded relics 
of the volcanoes of former geological   
periods4 ,the appearance of these works1
 in the years #ahbe and #ahbg           
respectively1 did much to prepare the   
minds of the earlier cultivators  of    
science for the reception of those      
doctrines of geological  uniformity and 
continuity1 which were shortly          
afterwards so ably  advocated by ,lyell 
in his ',principles of ,geology4'       
,since the date of the appearance of the
 last editions of ,scrope's  works1     
inquiry and speculation concerning the  
nature and origin of  volcanoes have    
been alike active1 and many of the      
problems which were  discussed by him1  
now present themselves under aspects    
entirely new and  different from those  
in which he was accustomed to regard    
them4 ,no one  was ever more ready to   
welcome original views or to submit to  
having  long-cherished principles       
exposed to the ordeal of free criticism 

than  was ,scrope2 and few men retained 
to so advanced an age the power of      
subjecting novel theories to the test of
 a rigorous comparison with  ascertained
 facts4    ,but this eminent geologist  
was not content with the devotion of his
  own time and energies to the          
advancement of his favourite science1   
for  as increasing age and growing      
infirmities rendered travel and personal
  research impossible1 he found a new   
source of pleasure in seeking  out the  
younger workers in those fields of      
inquiry which he had so  long and       
successfully cultivated1 and in         
furthering their efforts by  his        
judicious advice and kindly aid4 ,among 
the chosen disciples of  this           
distinguished man1 who will ever be     
regarded as one of the chief  pioneers  
of geological thought1 ,i had the good  
fortune to be numbered1  and when he    
committed to me the task of preparing a 
popular exposition  of the present      
condition of our knowledge on volcanoes1

 ,i felt that ,i  had been greatly      
honoured4    ,in order to keep the work 
within the prescribed limits1 and to    
avoid  unnecessary repetitions1 ,i have 
confined myself to the examination of   
such selected examples of volcanoes as  
could be shown to be really  typical of 
all the various classes which exist upon
 the globe2 and  ,i have endeavoured    
from the study of these to deduce those 
general  laws which appear to govern    
volcanic action4 ,but it has1 at the    
same time1 been my aim to approach the  
question from a somewhat new            
standpoint1 and to give an account of   
those investigations which have  in     
recent times thrown so much fresh light 
upon the whole problem4  ,in this way ,i
 have been led to dwell at some length  
upon subjects  which might not at first 
sight appear to be germane to the       
question  under discussion2--such as the
 characters of lavas revealed to us  by 
microscopic examination2 the nature and 
movements of the liquids  enclosed in   

the crystals of igneous rocks2 the      
relations of minerals  occurring in some
 volcanic products to those found in    
meteorites2 the  nature and origin of   
the remarkable iron-masses found at     
,ovifak in  ,greenland2 and the         
indications which have been discovered  
of analogies  between the composition   
and dynamics of our earth and those of  
other  members of the family of worlds  
to which it belongs4 ,while not evading 
the discussion of theoretical questions1
 ,i have endeavoured to keep  such      
discussions in strict subordination to  
that presentation of the  results       
attained by observation and experiment1 
which constitutes the  principal object 
of the work4    ,the woodcuts which     
illustrate the volume are in some cases 
prepared  from photographs1 and ,i am   
indebted to ,mr4 ,cooper for the skill  
with  which he has carried out my wishes
 concerning their reproduction4  ,others
 among the engravings are copies of     
sketches which ,i made in  ,italy1      

,hungary1 ,bohemia1 and other volcanic  
districts4 ,the whole of the            
wood-blocks employed by ,mr4 ,poulett   
,scrope in his work on ,volcanoes  were 
placed at my disposal before his death1 
and such of them as  were useful for my 
purpose ,i have freely employed4 ,to    
,captain ,s4 ,p4  ,oliver1 ,r4,a41 ,i am
 obliged for a beautiful drawing made in
 the ,island  of ,bourbon1 and to ,mr4  
,norman ,lockyer and his publishers1    
,messrs4  ,macmillan  ,co41 for the use 
of several wood-blocks illustrating     
sun-spots and solar prominences4        
,j4 ,w4 ,j4    ,london3 ,may #ahha4     
,,contents4                             
,,chapter ,i4                           
,,page                                  
,,introductory3 ,,nature ,,of ,,the     
,,enquiry                               
#a                                      
,,chapter ,,ii4                         
,,the ,,nature ,,of ,,volcanic ,,action 
#g                                      
,,chapter ,,iii4                        

,,the ,,products ,,of ,,volcanic        
,,action                                
#ci                                     
,,chapter ,,iv4         ,,the           
,,distribution ,,of ,,the ,,materials   
,,ejected ,,from ,,volcanic ,,vents     
#fg                                     
,,chapter ,v4                 ,,the     
,,internal ,,structure ,,of ,,volcanic  
,,mountains                             
#aab                                    
,,chapter ,,vi4             ,,the       
,,various ,,structures ,,built ,,up     
,,around ,,volcanic ,,vents             
#afa                                    
,,chapter ,,vii4         ,,the          
,,succession ,,of ,,operations ,,taking 
,,place ,,at ,,volcanic ,,centres       
#ahf                                    
,,chapter ,,viii4          ,,the        
,,distribution ,,of ,,volcanoes ,,upon  
,,the ,,surface ,,of ,,the ,,globe      
#bbd                                    
,,chapter ,,ix4          ,,volcanic     
,,action ,,at ,,different ,,periods ,,of

 ,,the ,,earth',s ,,history             
#bdg                                    
,,chapter ,x4             ,,the ,,part  
,,played ,,by ,,volcanoes ,,in ,,the    
,,economy ,,of ,,nature                 
#bha                                    
,,chapter ,,xi4                 ,,what  
,,volcanoes ,,teach ,,us ,,concerning   
,,the ,,nature                          
,,of ,,the ,,earth',s ,,interior        
#cjg                                    
,,chapter ,,xii4                 ,,the  
,,attempts ,,which ,,have ,,been ,,made 
,,to ,,explain                          
,,the ,,causes ,,of ,,volcanic ,,action 
#cca                                    
,,index                                 
#cga          ,,illustrations4          
,sections of igneous rocks illustrating 
the passage from the  glassy to the     
crystalline structure                   
,frontispiece      ,fig4                
,page       #a4 ,stromboli1 viewed from 
the north-west1 ,april #ahgd to face p4 
#aj       #b4 ,map of the ,island of    

,stromboli                              
#aa       #c4 ,section through the      
,island of ,stromboli from north-west to
          south-east                    
#ac       #d4 ,the crater of ,stromboli 
as viewed from the side of the          
,sciarra during an eruption on the      
morning of ,april #bd1          #ahgd4  
#ad       #e4 ,vesuvius in eruption1 as 
seen from ,naples1 ,april #bf1 #ahgb4   
7,from a photograph7                    
to face p4 #bd       #f4 ,view of       
,vulcano1 with ,vulcanello in the       
foreground--taken          from the     
south end of the ,island of ,lipari     
#dc       #g4 ,minute cavities1         
containing liquids1 in the crystals of  
rocks4          7,after ,zirkel7        
to face p4 #fj       #h4 ,minute        
liquid-cavity in a crystal1 with a      
moving bubble4          7,after         
,hartley7                               
#fc       #i4 ,cavity in crystal1       
containing carbonic-acid gas at a       
temperature of #hf ,f41 and passing from

 the liquid to          the gaseous     
condition4 7,after ,hartley7            
#fd      #aj4 ,monte ,nuovo 7#ddj ft    
high7 on the shores of the ,bay of      
,naples4          7,after ,scrope7      
#gf      #aa4 ,map of the district      
around ,naples1 showing ,monte ,nuovo   
and the          surrounding volcanoes  
of older date                           
#gh      #ab4 ,outlines of the summit of
 ,vesuvius during the eruption of       
#agfg4 7,after ,sir ,w4 ,hamilton7      
to face p4 #hj      #ac4 ,crater of     
,vesuvius formed during the eruption of 
#ahbb          7,after ,scrope7         
#hb      #ad4 ,crater of ,vesuvius in   
#agef1 from a drawing made on the spot4 
7,after ,sir ,w4 ,hamilton7             
#hd      #ae4 ,the summit of ,vesuvius  
in #agfg1 from an original drawing4     
7,after ,sir ,w1 ,hamilton7             
#he      #af4 ,summit of ,vesuvius in   
#ahdc                                   
#hf      #ag4 ,outlines of ,vesuvius1   
showing its form at different periods   

of its history                          
#hg      #ah4 ,cascade of lava tumbling 
over a cliff in the ,island of          
,bourbon4 7,after ,capt4 ,s4 ,p4        
,oliver1 ,r4,a47                  #ic   
#ai4 ,lava-stream 7obsidian7 in the     
,island of ,vulcano1 showing            
the imperfect liquidity of the mass     
#ie      #bj4 ,interior of a rhyolitic  
lava-stream in the ,island of ,lipari1  
showing broad1 sigmoidal folds1 produced
 by the slow          movements of the  
mass                                    
#if      #ba4 ,interior of a rhyolitic  
lava-stream in the ,island of ,lipari1  
showing the complicated crumplings and  
puckerings1          produced by the    
slow movements of the mass              
#if      #bb4 ,vesuvian lava-stream of  
#aheh1 exhibiting the peculiar          
'ropy' surfaces of slowly-moving        
currents4           7,from a photograph7
                          to face p4 #ih
      #bc4 ,vesuvian lava-stream of     
#ahgb1 exhibiting the rough cindery     

surfaces characteristic of rapidly      
flowing currents4          7,from a     
photograph7                           to
 face p4 #if      #bd4 ,concentric folds
 on mass of cooled lava4 7,after        
,heaphy7     #ajj      #be4 ,mass of    
cooled lava formed over a spiracle on   
the slopes          of ,hawaii4 7,after 
,dana7                                  
#ajj      #bf4 ,group of small cones    
thrown up on the ,vesuvian lava-current 
of #ahee4 7,after ,schmidt7             
#aja      #bg4 ,natural section of a    
lava-stream in the ,island of ,vulcano1 
showing the compact central portion and 
the scoriaceous          upper and under
 surfaces                               
#ajd      #bh4 ,section of a lava-stream
 exposed on the side of the river       
,ardche1 in the south-west of ,france4  
7,after ,scrope7      #ajf      #bi4    
,portion of a basaltic column from the  
,giant's ,causeway1          exhibiting 
both the ball-and-socket and the        
tenon-and-mortise structure             

#ajg      #cj4 ,vein of green pitchstone
 at ,chiaja di ,luna1 in the ,island    
of ,ponza1 breaking up into regular     
columns and into          spherical     
masses with a concentric series of      
joints4          7,after ,scrope7       
#ajh      #ca4 ,illustration of the     
'perlitic structure' in glassy rocks    
#aji      #cb4 ,transverse section of a 
lava-stream                             
#aaa      #cc4 ,the ,kammerbhl1 or      
,kammerberg1 ,bohemia 7as seen from     
the south-west7                         
#aac      #cd4 ,section of the          
,kammerbhl in ,bohemia                  
#aad      #ce4 ,natural section of a    
volcanic cone in the ,island of ,vulcano
   #aaf      #cf4 ,section in the side  
of the ,kammerbhl1 ,bohemia             
#aah      #cg4 ,experimental            
illustration of the mode of formation of
          volcanic cones1 composed of   
fragmental materials            #abj    
#ch4 ,natural section of a tuff-cone1   
forming the ,cape of ,misenum1          

and exhibiting the peculiar internal    
arrangement1          characteristic of 
volcanoes composed of fragmentary       
materials4 7,after ,scrope7             
#aba      #ci4 ,section of a small      
scoria-cone formed within the crater of 
,vesuvius in the year #ahce1            
illustrating the filling up of          
the central vent of the cone by         
subsequent ejections4          7,after  
,abich7                                 
#abb      #dj4 ,volcanic cones composed 
of scori1 and breached on one           
side by the outflow of lava-currents4   
7,after ,scrope7      #abh      #da4    
,campo ,bianco1 in the ,island of       
,lipari4 ,a pumice-cone                 
breached by the outflow of an obsidian  
lava-stream                             
to face p4 #abd      #db4 ,volcanic     
cones in ,auvergne1 which have suffered 
to some          extent from atmospheric
 denudation4 7,after ,scrope7           
#abd      #dc4 ,experimental            
illustration of the mode of formation of

          volcanic cones composed of    
viscid lavas4 7,after ,reyer7    #abf   
#dd4 ,the ,grand ,puy of ,sarcoui1      
composed of trachyte1 rising            
between two breached scoria-cones       
7,auvergne74 7,after          ,scrope7  
#abf      #de4 ,volcanic cone 7,mamelon7
 composed of very viscid lava           
7,island of ,bourbon74 7,after ,bory de 
,st4 ,vincent7          #abg      #df4  
,another ,mamelon in the ,island of     
,bourbon1 with a crater          at its 
summit4 7,after ,bory de ,st4 ,vincent7 
#abg      #dg4 ,cliff-section in the    
,island of ,madeira1 showing how a      
composite volcano is built up of        
lava-streams1 beds of          scori1   
and dykes4 7,after ,lyell7              
#abe      #dh4 ,section seen at the     
cascade1 ,bains du ,mont ,dore4 7,after 
,scrope7                                
#acj      #di4 ,section in the ,island  
of ,ventotienne1 showing a great        
stream of andesitic lava overlying      
stratified tuffs4          7,after      

,scrope7                                
#acj      #ej4 ,cliff on the south side 
of the ,island of ,san ,stephano        
#aca      #ea4 ,the headland of ,monte  
della ,guardia1 in the ,island of ,ponza
   #aca      #eb4 ,western side of the  
same headland1 as seen from the north   
side of ,luna ,bay                      
#acb      #ec4 ,sea-cliff at ,il ,capo1 
the north-east point of ,salina1        
showing stratified agglomerates         
traversed by numerous          dykes1   
the whole being unconformably overlaid  
by          stratified1 aqueous deposits
                                #acg    
#ed4 ,section observed in the ,val del  
,bove1 ,etna1 showing a                 
basaltic dyke1 from the upper part of   
which a          lava-current has flowed
                                        
#ach      #ee4 ,basaltic dykes          
projecting from masses of stratified    
scori          in the sides of the ,val 
del ,bove1 ,etna                        
#acd      #ef4 ,sheets of igneous rock  

7basalt7 intruded between beds of       
sandstone1 clay1 and limestone 7,island 
of ,skye7             #acg      #eg4    
,plan of the dissected volcano of ,mull 
in the ,inner          ,hebrides        
to face p4 #adb      #eh4 ,section of   
the volcano of ,mull along the line ,a  
,b            #adb      #ei4 ,summit of 
the volcano of ,monte ,sant' ,angelo1 in
 ,lipari1          exhibiting a crater  
with walls worn down by denudation      
#aeh      #fj4 ,outlines of lava-cones  
#afj      #fa4 ,diagram illustrating the
 formation of parasitic cones along     
lines of fissure formed on the flanks of
 a great volcanic          mountain     
#afb      #fb4 ,outline of ,etna1 as    
seen from ,catania                      
#afb      #fc4 ,outline of ,etna1 as    
seen from the ,val del ,bronte          
#afc      #fd4 ,plan of the volcano     
forming the ,island of ,ischia          
#afc      #fe4 ,a primary parasitic     
cone1 with a secondary one at its       
base--,ischia                           

#afd      #ff4 ,scoria-cone near        
,auckland1 ,new ,zealand1 with a        
lava-current          flowing from it4  
7,after ,heaphy7                        
#afe      #fg4 ,section of rocks below  
the ancient triassic volcano of         
,predazzo in the ,tyrol                 
#afe      #fh4 ,cotopaxi1 as seen from a
 distance of ninety miles4 7,after      
,humboldt7                              
#afh      #fi4 ,citlaltepetl1 or the    
,pic d',orizaba1 in ,mexico1 as seen    
from          the ,forest of ,xalapa4   
7,after ,humboldt7                      
#afi      #gj4 ,lac ,paven1 in the      
,auvergne4 7,after ,scrope7             
#aga      #ga4 ,the crater-lake called  
,lago del ,bagno1 in ,ischia1 converted 
into a harbour                          
#agb      #gb4 ,lake of ,gustavila1 in  
,mexico4 7,after ,humboldt7             
#agb      #gc4 ,peak of ,teneriffe1     
surrounded by great crater-rings4       
7,after          ,piazzi-,smyth7        
#age      #gd4 ,the volcano of ,bourbon1

 rising in the midst of a crater-ring   
four miles in diameter4 7,after ,bory de
 ,st4 ,vincent7       #agf      #ge4    
,the volcano of ,bourbon1 as seen from  
another point of          view1 with    
three concentric crater-rings encircling
 its          base4 7,after ,bory de    
,st4 ,vincent7                          
#agf      #gf4 ,vesuvius as seen from   
,sorrento1 half encircled by the        
crater-ring of ,somma                   
#agg      #gg4 ,outlines of various     
volcanoes illustrating the different    
relations of the craters to cones       
to face p4 #agh      #gh4 ,island thrown
 up ,in the ,mediterranean ,sea in ,july
 and          ,august1 #ahca4 7,after   
the ,prince de ,joinville7              
#agi      #gi4 ,sinter-cones surrounding
 the orifices of geysers                
#ahc      #hj4 ,diagram illustrating the
 mode of formation of travertine-       
and sinter-terraces on the sides of a   
hill of tuff          #ahe      #ha4    
,map of the volcanic group of the       

,lipari ,islands1 illustrating          
the position of the lines of fissure    
upon which          the volcanoes have  
been built up                           
#aib      #hb4 ,the ,puy de ,pariou1 in 
the ,auvergne1 illustrating the shifting
          of eruption along a line of   
fissures                        #aic    
#hc4 ,ideal section of the ,puy de      
,pariou                            #aid 
#hd4 ,fissure formed on the flanks of   
,etna during the emotion          of    
#ahfe4 7,after ,silvestri7              
#aid      #he4 ,plan of the ,island of  
,vulcano1 based on the map of the       
,italian ,government                    
#aif      #hf4 ,vulcanello1 with its    
three craters                           
#aig      #hg4 ,section of basalt from  
,ovifak1 ,greenland1 with particles of  
metallic iron diffused through its mass 
#cai      #hh4 ,diagram illustrating the
 relations between the terrestrial      
and the extra-terrestrial rocks         
to face p4 #cbb      #hi4 ,a group of   

sun-spots4 7,after ,secchi7             
#cfb      #ij4 ,a sun-spot1 showing the 
great masses of incandescent            
vapour rising or falling within it4     
7,after ,secchi7        #cfc      #ia4  
,the edge of a sun-spot1 showing a      
portion of the prominent          masses
 of incandescent gas 7,a7 which detached
 itself          at ,b and floated into 
the midst of the cavity4                
7,after ,norman ,lockyer7               
#cfc      #ib4 ,drawing of a solar      
prominence made by ,mr4 ,norman         
,lockyer1 ,march #ad1 #ahfi1 at #aa h4  
#e m4 ,a4,m4                 #cfd       
#ic4 ,the same object1 as seen at #aa h4
 #ae m4 on the same day4                
7,after ,norman ,lockyer7               
#cfe      #id4 ,drawings of a solar     
prominence at four different periods    
on ,september #g1 #ahga4 7,after ,young7
                       #cff      #ie4 ,a
 group of ,lunar craters 7,maurolycus1  
,barocius1 c471 the          largest    
being more than sixty miles in diameter 

#cfh          ,,volcanoes4              
,,chapter ,i4    ,,introductory3        
,,nature ,,of ,,the ,,inquiry4          
',what is a volcano8' ,this is a        
familiar question1 often addressed to us
  in our youth1 which ',catechisms of   
,universal ,knowledge1' and similar     
school manuals1 have taught us to reply 
to in some such terms as the  following3
 ',a volcano is a burning mountain1 from
 the summit of which  issue smoke and   
flames4' ,such a statement as this1 it  
is probable1 does  not unfairly         
represent the ideas which are1 even at  
the present day1  popularly entertained 
upon the subject4    ,but in this1 as in
 so many other cases1 our first step    
towards the  acquirement of scientific  
or exact knowledge1 must be the         
unlearning of  what we have before been 
led to regard as true4 ,the description 
which  we have quoted is not merely     
incomplete and inadequate as a whole1   
but each individual proposition of which
 it is made up is grossly  inaccurate1  

and1 what is worse1 perversely          
misleading4 ,in the first  place1 the   
action which takes place at volcanoes is
 not 'burning1' or  combustion1 and     
bears1 indeed1 no relation whatever to  
that well-known  process4 ,nor are      
volcanoes necessarily 'mountains' at    
all2 essentially1  they are just the    
reverse--namely1 holes in the earth's   
crust1 or  outer portion1 by means of   
which a communication is kept up between
  the surface and the interior of our   
globe4 ,when mountains do exist at      
centres of volcanic activity1 they are  
simply the heaps of materials  thrown   
out of these holes1 and must therefore  
be regarded not as the  causes but as   
the consequences of the volcanic action4
 ,neither does  this action always take 
place at the 'summits' of volcanic      
mountains1  when such exist1 for        
eruptions occur quite as frequently on  
their sides  or at their base4 ,that1   
too1 which popular fancy regards as     
'smoke'  is really condensing steam or  

watery vapour1 and the supposed raging  
'flames' are nothing more than the      
glowing light of a mass of molten       
material reflected from these vapour    
clouds4    ,it is not difficult to      
understand how these false notions on   
the  subject of volcanic action have    
come to be so generally prevalent4  ,in 
the earlier stages of its development1  
the human mind is much  more congenially
 employed in drinking in that which is  
marvellous  than in searching for that  
which is true4 ,it must be admitted1    
too1  that the grand and striking       
phenomena displayed by volcanoes are    
especially calculated to inspire terror 
and to excite superstition1  and such   
feelings most operate in preventing     
those close and accurate  observations  
which alone can form the basis of       
scientific reasoning4    ,sidenote3     
,,ideas ,,of ,,the ,,ancients4    ,the  
ancients were acquainted only with the  
four or five active  volcanoes in the   
,mediterranean area2 the term 'volcano' 

being the  name of one of these         
7,vulcano1 or ,volcano1 in the ,lipari  
,islands71  which has come to be applied
 to all similar phenomena4 ,it is only  
in  comparatively modern times that it  
has become a known act that many        
hundreds of volcanoes exist upon the    
globe1 and are scattered over  almost   
every part of its surface4 ,classical   
mythology appropriated  ,vulcano as the 
forge of ,hephstus1 and his ,roman      
representative ,vulcan1  while ,etna was
 regarded as formed by the mountains    
under which a  vengeful deity had buried
 the rebellious ,typhon2 it may be      
imagined1  therefore1 that any endeavour
 to more closely investigate the        
phenomena  displayed at these localities
 would be regarded1 not simply as an act
  of temerity1 but as one of actual     
impiety4 ,in medival times similar      
feelings would operate with not less    
force in the same direction1 for  the   
popular belief identified the           
subterranean fires with a place of      

everlasting torment2 ,vulcano was       
regarded as the place of punishment  of 
the ,arian ,emperor ,theodosius1 while  
,etna was assigned to poor ,anne        
,boleyn1 the perverter of faith in the  
person of its stoutest defender4  ,that 
such feelings of superstitious terror in
 connection with volcanoes  are1 even at
 the present day1 far from being        
extinct1 will be attested  by every     
traveller who1 in carrying on           
investigations about volcanic  centres1 
has had to avail himself of the         
assistance of guides and  attendants    
from among the common people4    ,among 
the great writers of antiquity we find  
several who had so far  emancipated     
their minds from the popular            
superstitions as to be able  to         
enunciate just and rational views upon  
the subject of volcanoes4  ,until quite 
recent times1 however1 their teaching   
was quite forgotten  or neglected1 and  
the modern science of ,vulcanology may  
be said to have  entirely grown up      

within the last one hundred years4      
,the great pioneer in this important    
branch of research was the  illustrious 
,italian naturalist ,spallanzani1 who1  
in the year #aghh1  visited the several 
volcanoes of his native land1 and       
published an  account of the numerous   
valuable and original observations which
 he  had made upon them4 ,about the same
 time the ,french geologist ,dolomieu   
showed how much light might be thrown on
 the nature of volcanic action  by a    
study of the various materials which are
 ejected from volcanic  vents2 while our
 own countryman4 ,sir ,william          
,hamilton1 was engaged in  a systematic 
study of the changes in form of volcanic
 mountains1 and  of the causes which    
determine their growth4 ,at a somewhat  
later date  the three ,german           
naturalists4 ,von ,buch1 ,humboldt1 and 
,abich1 greatly  extended our knowledge 
of volcanoes by their travels in        
different  portions of the globe4       
,sidenote3 ,,character ,,of ,,modern    

,,researches4    ,the first attempt1    
however1 to frame a satisfactory theory 
of volcanic  action1 and to show the    
part which volcanoes have played in the 
past  history of our globe1 together    
with their place in its present economy1
  was made in #ahbe1 by ,poulett        
,scrope1 whose great work1              
',considerations  on ,volcanoes1' may be
 regarded as the earliest systematic    
treatise on  ,vulcanology4 ,since the   
publication of this work1 many new lines
 of  inquiry have been opened up in     
connection with the subject1 and fresh  
methods of research have been devised   
and applied to it4 ,more exact          
observations of travellers over wider   
areas have greatly multiplied  the facts
 upon which we may reason and speculate1
 and many erroneous  hypotheses which   
had grown up in connection with the     
subject have been  removed by patient   
and critical inquiry4    ,we propose in 
the following pages to give an outline  
of the present  state of knowledge upon 

the subject1 and to indicate the        
bearings  of those conclusions which    
have already been arrived at1 upon the  
great questions of the history of our   
globe and the relations which  it bears 
to the other portions of the universe4  
,in attempting this  task we cannot do  
better than take up the several lines of
 inquiry  in the order in which they    
have been seized upon and worked out by 
the original investigators2 for never1  
perhaps1 is the development  of thought 
in the individual mind so natural in its
 methods1 and so  permanent in its      
effects1 as when it obeys those laws    
which determined  its growth in the     
collective mind of the race4 ,in our    
minds1 as in our  bodies1 development in
 the individual is an epitome1 or       
microcosmic  reproduction1 of evolution 
in the species4          ,,chapter ,,ii4
    ,,the ,,nature ,,of ,,volcanic      
,,action4      ,the dose investigation  
of what goes on within a volcanic vent  
may  appear at first sight to be a task 

beset with so many difficulties and     
dangers that we may be tempted to       
abandon it as altogether hopeless4 ,at  
the first recorded eruption of ,vesuvius
 the elder ,pliny lost his life  in an  
attempt to approach the mountain and    
examine the action which  was taking    
place there2 and during the last great  
outburst of the same  volcano a band of 
,neapolitan students1 whose curiosity   
was greater than  their prudence1 shared
 the same fate4    ,but in both these   
cases the inquirers paid the penalty of 
having  adopted a wrong method4 ,if we  
wish to examine the mode of working of a
  complicated steam-engine1 it will be  
of little avail for us to watch  the    
machinery when the full blast of steam  
is turned on1 and the rapid  movements  
of levers1 pinions1 and slides baffle   
all attempts to follow  them1 and render
 hopeless every effort to trace their   
connection with  one another4 ,but if   
some friendly hand turn off the greater 
part of  the steam-supply1 then1 as the 

rods move slowly backwards and forwards1
  as the wheels make their measured     
revolutions1 and the valves axe  seen   
gradually opening and shutting1 we may  
have an opportunity of  determining the 
relations of the several parts of the   
machine to one  another1 and of arriving
 at just conclusions concerning the plan
 on  which it is constructed4 ,nor can  
we doubt that the parts of the machine  
bear the same relation to one another1  
and that their movements take  place in 
precisely the same order1 when the      
supply of steam is large as  when it is 
small4    ,now1 as we shall show in the 
sequel1 a volcano is a kind of great    
natural steam-engine1 and our best      
method of investigating its action  is  
to watch it when a part of the          
steam-supply is cut off4 ,it is  true   
that we cannot at will control the      
source of supply of steam to  a volcano1
 as we can in a steam-engine1 but as    
some volcanoes have  usually only a     
small steam-supply1 and nearly all      

volcanoes vary  greatly in the intensity
 of their action at different periods1  
we can1  by a careful selection of the  
object or the time of our study1 gain   
all  those advantages which would be    
obtained by regulating its action for   
ourselves4    ,spallanzani appears to   
have been the first to perceive the     
important  fact1 that the nature of     
volcanic action remains the same1       
however  its intensity may vary4 ,taking
 advantage of the circumstance that     
there exists in the ,mediterranean ,sea 
a volcano--,stromboli--which  for at    
least #b1jjj years has been in a        
constant and regular1 but not  in a     
violent or dangerous1 state of activity1
 he visited the spot1  and made the     
series of careful observations which    
laid the foundation  of our knowledge of
 the 'physiology of volcanoes4' ,since  
the time  of ,spallanzani1 many other   
investigators have visited the crater   
of ,stromboli1 and they have been able  
to confirm and extend the  observations 

of the great ,italian naturalist1 as to 
the character of  the action which is   
constantly taking place within it4 ,we  
cannot better  illustrate the nature of 
volcanic action than by describing what 
has  been witnessed by numerous         
observers within the crater of          
,stromboli1  where it is possible to    
watch the series of operations going on 
by the  hour together1 and to do so     
without having our judgment warped      
either  by an excited imagination or the
 sense of danger4    ,sidenote3         
,,appearance ,,of ,,stromboli ,,from ,a 
,,distance4    ,in the sketch1 fig4 #a1 
which was made on ,april #bj1 #ahgd1 ,i 
have shown  the appearance which this   
interesting volcano usually presents1   
when  viewed from a distance4 ,the      
island is of rudely circular outline1   
and  conical form1 and rises to the     
height of #c1jij feet above the level of
  the ,mediterranean4 ,from a point on  
the side of the mountain1 masses  of    
vapour are seen to issue1 and these     

unite to form a cloud over  the         
mountain1 the outline of this           
vapour-cloud varying continually        
according to the hygrometric state of   
the atmosphere1 and the direction  and  
force of the wind4 ,at the time when    
this sketch was made1 the  vapour-cloud 
was spread in a great horizontal stratum
 overshadowing  the whole island1 but it
 was clearly seen to be made up of a    
number  of globular masses1 each of     
which1 as we shall hereafter see1 is the
  product of a distinct outburst of the 
volcanic forces4    ,viewed at          
night-time1 ,stromboli presents a far   
more striking and  singular spectacle4  
,the mountain1 with its vapour canopy1  
is visible  over an area having a radius
 of more than #ajj miles4 ,when watched 
from  the deck of a vessel anywhere     
within this area1 a glow of red light is
  seen to make its appearance from time 
to time above the summit of the         
mountain2 this glow of light may be     
observed to increase gradually in       

intensity1 and then as gradually to die 
away4 ,after a short interval  the same 
appearances are repeated1 and this goes 
on till the increasing  light of the    
dawn causes the phenomenon to be no     
longer visible4 ,the  resemblance       
presented by ,stromboli to a 'flashing  
light' on a most  gigantic scale is very
 striking1 and the mountain has long    
been known  as 'the lighthouse of the   
,mediterranean4'    ,it must be pointed 
out1 however1 that in two very important
 particulars  the appearances presented 
by ,stromboli differ markedly from those
  rhythmical gleams exhibited by the    
'flashing-lights' of our coasts4  ,in   
the first place1 the intervals between  
successive flashes are very  unequal1   
varying from less than one minute to    
twenty minutes1 or even  more2 and in   
the second place1 the duration and      
intensity of the red  glow above the    
mountain are subject to like variation1 
being sometimes  a momentary scarcely   
visible gleam1 and at others a vivid    

burst of  light which illuminates the   
sky to a considerable distance round4   
,illustration3 ,fig4 #a4--,stromboli1   
viewed from the ,north-west1 ,april     
#ahgd4    ,illustration3 ,fig4 #b4--,map
 of tub ,island of ,stromboli4 7,scale  
about  two inches to a mile47           
,sidenote3 ,,general ,,features ,,of    
,,the ,,mountain4    ,let us now draw   
near and examine this wonderful         
phenomenon of a  mountain which         
seemingly ever burns with fire1 and yet 
is not consumed4  ,the general form of  
the ,island of ,stromboli will be       
gathered from an  inspection of the     
plan1 fig4 #b1 which is copied from a   
map published by  the ,italian          
,government4 ,when we land upon the     
island1 we find that it  is entirely    
built up of such materials as we know to
 be ejected from  volcanoes2 indeed1 it 
resembles on a gigantic scale the       
surroundings  of an iron furnace1 with  
its heaps of cinders and masses of slag4
 ,the  irregularity in the form of the  

island is at once seen to be due to the 
action of the wind1 the rain1 and the   
waves of the surrounding sea1  which    
have removed the loose1 cindery         
materials at some points1 and  left the 
hard1 slaggy masses standing up         
prominently at others4    ,this great   
heap of cindery and slaggy materials    
rises1 as we have said1  to a height of 
more than #c1jjj feet above the         
sea-level1 but even this  measurement   
does not give a just idea of its vast   
bulk4 ,soundings in  the sea surrounding
 the island show that the bottom        
gradually shelves  around the shores to 
the depth of nearly #fjj fathoms1 so    
that ,stromboli  is a great conical mass
 of cinders and slaggy materials1 having
 a  height of over #f1jjj feet1 and a   
base whose diameter exceeds four miles4 
,the general form and proportions of    
this mass will be better understood  by 
an examination of the section1 fig4 #c1 
which is also constructed  from the     
materials furnished by the map of the   

island issued by the  ,italian          
,government4 ,the same section1 and the 
map1 fig4 #b1 will serve  to make clear 
the position and relations of the point 
on the mountain  at which the volcanic  
activity takes place4 ,at a spot on the 
north-west  slope of the mountain1 about
 #a1jjj feet below its summit1 and      
#b1jjj  feet above the level of the sea1
 there exists a circular depression1    
the present active 'crater' of the      
volcano2 and leading down from this  to 
the sea there is a flat slope making an 
angle of about #ce with the  horizon1   
and known as the ',sciarra4' ,the       
,sciarra is bounded by steep  cliffs1 as
 shown in the sketch fig4 #a1 and the   
plan fig4 #b4    ,illustration3 ,fig4   
#c4--,section through the ,island of    
,stromboli from  n4w4 to s4e4    a4     
,highest summit of the mountain1 c4     
,cratre del ,fossa1 b4 ,point           
overlooking the crater1 d4 ,steep slope 
known as the ,sciarra del  ,fuoco4 e4   
,continuation of the same slope beneath 

the level of the  sea4 f4 ,steep cliffs 
of the ,punta dell' ,omo4    ,sidenote3 
,,form ,,and ,,function ,,of ,,the      
,,crater4    ,if we climb up to this    
scene of volcanic activity1 we shall be 
able to  watch narrowly the operations  
which are going on there4 ,on the       
morning  of the #bdth of ,april1 #ahgd1 
,i paid a visit to this interesting spot
 in  order to get a near view of what   
was taking place4 ,on reaching a point  
upon the side of the ,sciarra1 from     
which the crater was in full view       
before me1 ,i witnessed1 and made a     
sketch of1 an outburst which then  took 
place1 and this sketch has been         
reproduced in fig4 #d4 ,before the      
outburst1 numerous light curling wreaths
 of vapour were seen ascending  from    
fissures on the sides and bottom of the 
crater4 ,suddenly1 and  without the     
slightest warning1 a sound was heard    
like that produced  when a locomotive   
blows off its steam at a                
railway-station2 a great  volume of     

watery vapour was at the same time      
thrown violently into  the atmosphere1  
and with it there were hurled upwards a 
number of  dark fragments1 which rose to
 the height of #djj or #ejj feet above  
the  crater1 describing curves in their 
course1 and then falling back upon  the 
mountain4 ,most of these fragments      
tumbled into the crater with a  loud1   
rattling noise1 but some of them fell   
outside the crater1 and a  few rolled   
down the steep slope of the ,sciarra    
into the sea4 ,some of  these falling   
fragments were found to be still hot and
 glowing1 and in  a semi-molten         
condition1 so that they readily received
 the impression  of a coin thrust into  
them4    ,illustration3 ,fig4 #d4--,the 
,crates of ,stromboli as viewed from the
 side  of the ,sciarra during an        
eruption on the morning of ,april #bd1  
#ahgd4    ,sidenote3 ,,apertures ,,at   
,,the ,,bottom ,,of ,,the ,,crater4     
,but on the upper side of the crater1 at
 the point marked #f1 on the  section   

fig4 #c1 there exists a spot from which 
we can look down upon  the bottom of the
 crater1 and view the operations taking 
place there4  ,this is the place where  
,spallanzani and other later            
investigators have  carried on their    
observations1 and1 when the wind is     
blowing from  the spectator towards the 
crater1 he may sit for hours watching   
the  wonderful scene displayed before   
him4 ,the black slaggy bottom of the    
crater is seen to be traversed by many  
fissures or cracks1 from most  of which 
curling jets of vapour issue quietly1   
and gradually mingle  with and disappear
 in the atmosphere4 ,but besides these  
smaller cracks  at the bottom of the    
crater1 several larger openings are     
seen1 which  vary in number and position
 at different periods2 sometimes only   
one of  these apertures is visible1 at  
others as many as six or seven1 and the 
phenomena presented at these larger     
apertures are especially worthy of      
careful investigation4    ,these larger 

apertures1 if we study the nature of the
 action taking  place at them1 may be   
divided into three classes4 ,from those 
of the  first class1 steam is emitted   
with loud1 snorting puffs1 like those   
produced by a locomotive-engine1 but far
 less regular and rhythmical  in their  
succession4 ,in the second class of     
apertures masses of molten  material are
 seen welling out1 and1 if the position 
of the aperture  be favourable1 flowing 
outside the crater2 from this liquid    
molten  mass steam is seen to escape1   
sometimes in considerable quantities4   
,the openings of the third class present
 still more interesting  appearances4   
,within the walls of the aperture a     
viscid or semi-liquid  substance is seen
 slowly heaving up and down4 ,as we     
watch the seething  mass the agitation  
within it is observed to increase       
gradually1 and at  last a gigantic      
bubble is formed which violently bursts1
 when a great  rush of steam takes      
place1 carrying fragments of the        

scum-like surface  of the liquid high   
into the atmosphere4    ,if we visit the
 crater by night1 the appearances       
presented are found to  be still more   
striking and suggestive4 ,the smaller   
cracks and larger  openings glow with a 
ruddy light4 ,the liquid matter is seen 
to be red-  or even white-hot1 while the
 scum or crust which forms upon it is of
 a  dull red colour4 ,every time a      
bubble bursts and the crust is broken up
  by the escape of steam1 a fresh1      
glowing surface of the incandescent     
material is exposed4 ,if at these       
moments we look up at the vapour-cloud  
covering the mountain1 we shall at once 
understand the cause of the  singular   
appearances presented by ,stromboli when
 viewed from a distance  at night1 for  
the great masses of vapour are seen to  
be lit up with a  vivid1 ruddy glow1    
like that produced when an engine-driver
 opens the  door of the furnace and     
illuminates the stream of vapour issuing
 from  the funnel of his locomotive4    

,let us now endeavour to analyse the    
phenomena so admirably displayed  before
 us in the crater of ,stromboli4 ,the   
three essential conditions  on which the
 production of these phenomena seems to 
depend are the  following3 first1 the   
existence of certain apertures or cracks
  communicating between the interior and
 the surface of the earth2  secondly1   
the presence of matter in a highly      
heated condition beneath  the surface2  
and thirdly1 the existence of great     
quantities of water  imprisoned in the  
subterranean regions--which water1      
escaping as steam1  gives rise to all   
those active phenomena we have been     
describing4    ,sidenote3 ,,cause ,,of  
,,the ,,glowing ,,light4    ,we have    
said1 at the outset1 that there exists  
no analogy whatever  between the action 
which takes place in volcanoes and the  
operation of  burning or combustion4    
,occasionally1 it is true1 certain      
inflammable  substances are formed by   
the action going on within the volcano1 

and  these inflammable substances1      
taking fire1 produce real flames4 ,such 
flames are1 however1 in almost all cases
 only feebly luminous1 and do  not give 
rise to any conspicuous appearances4    
,what is usually taken for  flame during
 volcanic eruptions is simply1 as we    
have already pointed  out1 the glowing  
red-hot surface of a mass of molten     
rock1 reflected  from a vapour-cloud    
hanging over it4 ,the red glow observed 
over a  volcano in eruption is indeed   
precisely similar in its nature and     
origin to that which is seen above      
,london during a night of heavy fog1    
and which is produced by the reflection 
of the gas-lights of the city  from the 
innumerable particles of water-vapour   
diffused through the  atmosphere4       
,fires1 of course1 occur when the molten
 and incandescent  materials poured out 
from a volcano come in contact with     
inflammable  substances1 such as forests
 and houses1 but in these cases the     
combustion is quite a secondary         

phenomenon4    ,there is another popular
 delusion concerning volcanic action1   
which it  may be necessary to refer to  
and to combat4 ,from the well-known fact
  that sulphur or brimstone is found    
abundantly in volcanic regions1 the     
popular belief has arisen that this     
highly inflammable substance has        
something to do with the production of  
the eruptions of volcanoes4 ,in         
school-books which were1 until          
comparatively recent years1 in constant 
use in this country1 the statement may  
be found that by burying certain        
quantities of sulphur1 iron-pyrites1 and
 charcoal in a hole in the  ground1 we  
may form a miniature volcano1 and       
produce all the essential  phenomena of 
a volcanic eruption4 ,no greater mistake
 could possibly be  made4 ,the chemical 
reactions which take place when sulphur 
and other  substances are made to act   
upon each other differ entirely from the
  phenomena of volcanic action4 ,the    
sulphur which is found in volcanic      

regions is the result and not the cause 
of volcanic action4 ,among the  most    
common substances emitted from volcanic 
vents along with the steam  are the two 
gases1 sulphurous acid and sulphuretted 
hydrogen4 ,when  these two gases come   
into contact with one another1 chemical 
action  takes place1 and the elements   
contained in them--oxygen1 hydrogen1    
and sulphur--are free to group          
themselves together in an entirely new  
fashion2 the consequence of this is that
 water and sulphuric acid 7oil  of      
vitriol7 are formed1 and a certain      
quantity of sulphur is set free4  ,the  
water escapes into the atmosphere1 the  
sulphuric acid combines with  lime1     
iron1 or other substances contained in  
the surrounding rocks1  and the sulphur 
builds up crystals in any cavities which
 may happen to  exist in these rocks4   
,sidenote3 ,,volcanic ,,action          
,,resembles ,,boiling4    ,if1 however1 
careful and exact observations1 like    
those carried on  at ,stromboli1 compel 

us to reject the popular notions        
concerning  the supposed resemblance    
between volcanic action and the         
combustion  of sulphur or other         
substances1 they nevertheless suggest   
analogies  with certain other simple and
 well-known operations4 ,and in pursuing
  these analogies1 we are led to the    
recognition of some admirable           
illustrations both of the attendant     
phenomena and of the true cause of      
volcanic outbursts4    ,no one can look 
down on the mass of seething material in
 violent  agitation within the fissures 
at the bottom of the crater of          
,stromboli1  without being forcibly     
reminded of the appearances presented by
 liquids  in a state of boiling or      
ebullition4 ,the glowing material seems 
to be  agitated by two kinds of         
movements1 the one whirling or rotatory1
 the  other vertical or up-and-down in  
its direction4 ,the fluid mass in this  
way appears to be gradually impelled    
upwards1 till it approaches the  lips of

 the aperture1 when vast bubbles are    
formed upon its surface1  and to the    
sudden bursting of these the phenomena  
of the eruption are  due4    ,now if we 
take a tall narrow vessel and fill it   
with porridge or  some similar substance
 of imperfect fluidity1 we shall be     
able1 by  placing it over a fire1 to    
imitate very closely indeed the         
appearances  presented in the crater of 
,stromboli4 ,as the temperature of the  
mass  rises1 steam is generated within  
it1 and in the efforts of this steam  to
 escape1 the substance is set in violent
 movement4 ,these movements of  the mass
 are partly rotatory and partly vertical
 in their direction2 as  fresh steam is 
generated in the mass its surface is    
gradually raised1  while an escape of   
the steam is immediately followed by a  
fall of the  surface4 ,thus an          
up-and-down movement of the liquid is   
maintained1 but  as the generation of   
steam goes on faster than it can escape 
through  the viscid mass1 there is a    

constant tendency in the latter to rise 
towards the mouth of the vessel4 ,at    
last1 as we know1 if heat continues  to 
be applied to the vessel1 the fluid     
contents will be forced up to  its edge 
and a catastrophe will occur2 the steam 
being suddenly and  violently liberated 
from the bubbles formed on the surface  
of the mass1  and a considerable        
quantity of the material forcibly       
expelled from  the vessel4 ,the         
suddenness and violence of this         
catastrophe is easily  accounted for1 if
 we bear in mind that the escaping steam
 acts after  the manner of a compressed 
spring which is suddenly released4      
,steam  is first formed at the bottom of
 the vessel which is in contact with    
the fire2 but here it is under the      
pressure of the whole mass of the       
liquid1 and moreover1 the viscidity of  
the substance tends to retard  the union
 of the steam bubbles and their rise to 
the surface of the  mass4 ,but when the 
pressure is relieved by the bursting of 

bubbles at  the surface1 the whole of   
the generated steam tends to escape     
suddenly4    ,sidenote3 ,,escape ,,of   
,,steam-,,bubbles ,,from ,,lava4        
,now within the crater of ,stromboli we 
have precisely the necessary  conditions
 for the display of the same series of  
operations4 ,in the  apertures at the   
bottom there exists a quantity of       
imperfectly fluid  materials at a higher
 temperature1 containing water entangled
 in its  mass4 ,as this water passes    
into the state of steam it tends to     
escape1  and in so doing puts the whole 
mass into violent movement4 ,when the   
steam rises to the surface1 bubbles are 
formed1 and the formation of  these     
bubbles is promoted by the circumstance 
that the liquid mass1  where exposed to 
the atmosphere1 becomes chilled1 and    
thereby rendered  less perfectly fluid4 
,by the bursting of these bubbles the   
pressure is  partially relieved1 and a  
violent escape of the pent-up steam     
takes  place through the whole mass4    

,equilibrium being thus restored1 there 
follows a longer or shorter interval of 
quiescence1 during which steam  is being
 generated and collected within the     
mass1 and the series of  operations     
which we have described then            
recommences4    ,there is one other     
consideration which must be borne in    
mind in  connection with this subject4  
,it is well known that if water be      
subjected to sufficiently great pressure
 it may be raised to a very  high       
temperature and still retain its liquid 
condition4 ,when this  pressure is      
removed1 however1 the whole mass passes 
at once into the  condition of steam or 
water-gas2 and the gas thus formed at   
high  temperatures has a proportionably 
high tension4 ,in a ,papin's digester   
water confined in a strong vessel is    
raised to temperatures far above  its   
ordinary boiling-point1 and from any    
opening in such a vessel the  steam     
escapes with prodigious violence4 ,now1 
at considerable depths  beneath the     

earth's surface1 and under the pressure 
of many hundreds  or thousands of feet  
of solid rock1 water still retaining its
 liquid  condition may become intensely 
heated4 ,when the pressure is relieved  
by  the formation of a crack or fissure 
in the superincumbent mass of rock1  the
 escape of the superheated steam will be
 of very violent character1  and may be 
attended with the most striking and     
destructive results4 ,in  the existence 
of high temperatures beneath the earth's
 surface1 and the  presence in the same 
regions of imprisoned water capable of  
passing  into the highly elastic gas    
which we call steam1 we have a cause    
fully  competent to produce all the     
phenomena which we have described as    
occurring at ,stromboli4    ,it may at  
first sight appear that the grand and   
terrible displays  of violence witnessed
 during a great volcanic eruption differ
  fundamentally in their character and  
their origin from those feeble          
outbursts which we are able to examine  

closely and analyse rigorously  at      
,stromboli4 ,but that such is not the   
case a few simple considerations  will  
soon convince us4    ,sidenote3         
,,stromboli ,,compared ,,with           
,,vesuvius4    ,although ,stromboli     
usually displays the subdued and        
moderate activity  which we have been   
describing1 yet the intensity of the    
action going  on within it is subject to
 considerable variation4 ,occasionally  
the  violence of the outbursts is       
greatly increased--the roaring of the   
steam-jets may be heard for many miles  
around1 considerable streams of         
incandescent liquefied rock flow down   
the ,sciarra into the sea1 and the      
explosions in the crater are far more   
frequent and energetic1 cinders  and    
fragments of rock being scattered all   
over the island and the  surrounding    
seas4    ,on the other hand1 volcanoes  
like ,vesuvius1 which are sometimes the 
scene of eruptions on the very grandest 
scale1 at others subside into a         

temporary state of moderate activity    
quite similar in character to that      
which is the normal condition of        
,stromboli4 ,thus1 shortly before the   
great eruption of ,vesuvius in ,april   
#ahgb1 a small cone was formed near  the
 edge of the crater1 and during some    
months observers could watch1  in ease  
and safety1 a series of small explosions
 taking place1 quite  similar in their  
character and attendant phenomena to    
those which we  have described as       
occurring at ,stromboli4 ,french        
geologists are in the  habit of defining
 the condition of activity in a volcano 
by speaking  of the more quiet and1     
regular state as the ',strombolian      
stage1' and  the more violent and       
paroxysmal as the ',vesuvian stage'2 but
 the two  conditions are1 as we have    
seen1 presented by the same volcano at  
different periods1 and pass into one    
another by the most insensible          
gradations4    ,we must now proceed to  
compare the grand and terrible          

appearances  presented during a great   
eruption with those more feeble displays
 which  we have been describing1 to show
 that in all their essential features   
these different kinds of outbursts are  
identical with one another1 and  must be
 referred to the action of similar      
causes4    ,the volcanic eruption which 
has been most carefully studied in      
recent  times is that which we have     
already referred to as occurring at     
,vesuvius1 in the month of ,april #ahgb4
 ,with the exception1 perhaps1 of  that 
which took place in ,october #ahbb1 this
 eruption was the grandest  which has   
broken out at ,vesuvius during the      
present century4 ,owing to  the         
circumstance of its proximity to the    
great city of ,naples1 ,vesuvius  has   
always been the most carefully watched  
of all volcanoes1 and in  recent years  
the erection of an observatory1 provided
 with instruments  for recording the    
smallest subterranean tremors affecting 
the mountain1  has facilitated the      

carrying on of those continuous and     
minute  observations which are so       
necessary for exact scientific inquiry4 
,illustration3 ,fig #e4 ,vesuvius in    
,eruption1 as seen from ,naples1 ,april 
#bf1 #ahgb4 7,from a photograph7        
,sidenote3 ,,vesuvius ,,eruption ,,of   
#ahgb4    ,on the occasion of this      
outburst1 the aid of instantaneous      
photography  was first made available   
for obtaining a permanent record of the 
appearances displayed at volcanic       
eruptions4 ,in fig4 #e we have one of   
these photographs1 which was taken at #e
 o'clock ,p4,m4 on ,april #bf1 #ahgb1   
transferred to a wood-block and         
engraved4 ,in examining it we feel sure 
that we are not being misled by any     
exaggeration or error on the part  of   
the artist4 ,vesuvius rises to the      
height of nearly #d1jjj feet above  the 
level of the sea1 and an inspection of  
the photograph proves that  the vapours 
and rock-fragments were thrown to the   
enormous height of  #bj1jjj feet1 or    

nearly four miles1 into the atmosphere4 
,the main features of this terrifying   
outburst were as follows4 ,for  more    
than a twelvemonth before1 the activity 
of the forces at work  within the       
mountain appeared to be gradually       
increasing1 and the great  eruption     
commenced on ,april #bd1 attained its   
climax on the #bfth1 and  began to die  
out on the following day4 ,during the   
eruption the bottom  of the crater was  
entirely broken up1 and the sides of the
 mountain  were rent by fissures in all 
directions4 ,so numerous were these     
fissures and cracks that liquid matter  
appeared to be oozing from every  part  
of its surface1 and1 as ,professor      
,palmieri1 who witnessed the  outburst  
from the observatory1 expressed it1     
',vesuvius sweated fire4'  ,one of the  
fissures was of enormous size1 extending
 from the summit to  far beyond the base
 of the cone2 the scar left by this     
gigantic rent  being plainly visible at 
the present day4    ,from the great     

opening or crater at the summit1 and    
from some of the  fissures on the sides 
of the mountain1 enormous volumes of    
steam rushed  out with a prodigious     
roaring sound1 the noise being so       
terrific that  the inhabitants of       
,naples1 five miles off1 fled from their
 houses  and spent the night in the open
 streets4 ,although this roaring sound  
appeared at a distance to be continuous1
 yet those upon the mountain  could     
perceive that it was produced by        
detonations or explosions  rapidly      
following one another4 ,each of these   
explosions was accompanied  by the      
formation of a great globe of white     
vapour1 which1 rising into  the         
atmosphere1 swelled the bulk of the vast
 cloud overhanging the  mountain4 ,an   
inspection of the photographs 7see fig4 
#e7 shows that the  great vapour-cloud  
over ,vesuvius was made up of the       
globular masses  ejected at successive  
explosions4 ,each of these explosive    
upward  rushes of steam carried along   

with it a considerable quantity of solid
  fragments1 and these fell in great    
numbers all over the surface of  the    
mountain1 breaking the windows of the   
observatory1 and making it  dangerous to
 be out of doors4    ,we have said that 
lava1 or molten rock1 appeared to be    
issuing from  the very numerous cracks  
formed all over the flanks of the       
mountain4  ,but at three points this    
molten rock issued in such quantities as
 to  form great1 fiery floods1 which    
rushed down the sides of the mountain1  
and flowed to a considerable distance   
beyond its base4 ,the largest  of these 
lava-floods overwhelmed and destroyed   
the two villages of  ,massa di ,somma   
and ,san ,sebastiano1 besides many      
country houses in the  neighbourhood4   
,sidenote3 ,,steam ,,emitted ,,from     
,,lava-,,current4    ,a very marked and 
interesting feature exhibited by these  
three  lava-floods was the quantity of  
watery vapour which they gave off       
during their flow4 ,all along their     

course1 enormous volumes of steam  were 
evolved from them1 as will be seen by an
 inspection of the  photograph4 ,indeed1
 such was the abundance and tension of  
the steam  thus escaping from the       
surfaces of the lava-currents that it   
forced  the congealing rock up into     
great bubbles and blisters1 and gave    
rise  to the formation of innumerable   
miniature volcanoes1 varying in size    
from a beehive to a cottage1 some of    
which remained in a state of            
independent activity for a considerable 
time4    ,so far1 what we have described
 as taking place at ,vesuvius1 in ,april
  #ahgb1 has been only the repetition on
 a ,eur grander scale of the  three     
kinds of action which we have shown to  
be constantly taking  place at          
,stromboli2 namely1 the formation of    
cracks or fissures in the  earth's      
surface1 the escape of steam with       
explosive violence from these  openings1
 often propelling rock-fragments into   
the atmosphere1 and the  outwelling1    

under the influence of this compressed  
steam1 of masses of  molten materials4  
,there were some other appearances      
presented at the great outburst at      
,vesuvius1 which do not seem at first   
sight to find any analogies in  the     
manifestations of the more feeble action
 continually going on at  ,stromboli4   
,before and during the great outbreak of
 ,april #ahgb1 ,vesuvius itself  and the
 whole country round were visited with  
earthquake-shocks1 or  tremblings of the
 ground4 ,the sensitive instruments in  
the ,vesuvian  ,observatory showed the  
mountain daring the eruption to be in a 
constant  state of tremor4 ,these       
earthquakes are not1 as is commonly     
supposed1  actual upheavings of the     
earth's surface1 but are vibrations     
propagated  through the solid materials 
of which the earth is built up4 ,we     
cannot  stamp our feet upon the ground  
without giving rise to such vibrations1 
though our senses may not be            
sufficiently acute to perceive them4    

,the explosive escape of steam from a   
crack is a cause sufficiently  powerful 
to produce a shock which is propagated  
and may be felt for  a considerable     
distance round4 ,even on ,stromboli an  
observer at the  edge of the crater may 
notice that each explosive outburst of  
steam  is accompanied by a perceptible  
tremor of the ground1 and in the case   
of ,vesuvius the violent shocks produced
 by the escape of far larger  volumes of
 steam give rise to proportionately     
stronger vibrations4 ,the  nature and   
origin of those far more terrible and   
destructive shocks  which sometimes     
accompany1 and more frequently precede1 
great volcanic  eruptions1 we shall     
consider in the sequel4    ,sidenote3   
,,cause ,,of ,,lightning ,,during       
,,eruptions4    ,another striking       
phenomenon which was exhibited in the   
great eruption  of ,vesuvius in #ahgb   
was the vivid display of lightning      
accompanied  by thunder4 ,the uprushing 
current of steam and rock-fragments     

forms  a vertical column1 but as the    
steam condenses it spreads out into a   
great horizontal cloud which is seen to 
be made up of the great globes  of      
vapour emitted at successive explosions4
 ,when there is little or  no wind the  
vertical column with a horizontal cloud 
above it bears a  striking resemblance  
to the stone-pine trees which form so   
conspicuous  a feature in every         
,neapolitan landscape4 ,around this     
column of vapour  the most vivid        
lightning constantly plays and adds not 
a little to the  grand and awful        
character of the spectacle of a volcanic
 eruption1  especially when it is viewed
 by night4    ,in the eruption of #ahgb 
a strong wind blowing from the          
north-west  destroyed the usual regular 
appearance of this 'pine-tree appendage'
 to  the mountain1 which is so well     
known to1 and dreaded by the inhabitants
  of ,naples2 the cloud1 as will be seen
 from the photograph 7fig4 #e1  facing  
p4 #bd71 was blown on one side1 and most

 of the falling  fragments took the same
 direction4    ,it is well known that   
when high-pressure steam is allowed to  
escape  through an orifice1 electricity 
is abundantly generated by the          
friction1 and ,sir ,william ,armstrong's
 hydro-electric machine is  constructed 
on this principle4 ,every volcano in    
violent eruption is  a very efficient   
hydro-electric machine1 and the         
uprushing column  is in a condition of  
intense electrical excitation4 ,this    
result is  probably aided by the        
friction of the solid particles as they 
are  propelled upwards and fall back    
into the crater4 ,the restoration of    
the condition of electrical stability   
between this column and the  surrounding
 atmosphere is attended with the        
production of frequent                  
lightning-flashes and thunder-claps1 the
 found of the latter being  usually1    
however1 drowned in the still louder    
roar of the uprushing  steam-column4    
,the discharge of ,buch large quantities

 of steam into the atmosphere  soon     
causes the latter to be saturated with  
watery vapour1 and there  follows an    
excessive rainfall2 long-continued rain 
and floods were an  accompaniment of the
 great ,vesuvian outbreak of #ahgb1 as  
they have  been of almost all great     
volcanic eruptions4 ,the ,italians1     
indeed1  dread the floods which follow  
an eruption more than the fiery streams 
of lava which accompany it--for they    
have found the mud-streams 7lave  di    
fango71 formed by rain-water sweeping   
along the loose volcanic  materials1 to 
be more widely destructive in their     
effects than the  currents of molten    
rock 7lave di fuoco74    ,besides the   
phenomena which we have now described as
 accompanying a  great volcanic         
outburst1 many others have undoubtedly  
been recorded  by apparently trustworthy
 authorities4 ,but1 in dealing with the 
descriptions of these grand and terrible
 events1 we must always be on  our guard
 against accepting as literal facts1 the

 statements made by  witnesses1 often   
writing at some distance from the scene 
of action1 and  almost always under the 
influence of violent excitement and     
terror4  ,the desire to administer to   
the universal love of the marvellous1   
and  the tendency to exaggeration1 will 
usually account for many of the         
wonderful statements contained in such  
records2 and1 even where the  witness is
 accurately relating events which he    
thinks passed before his  eyes1 we must 
remember that it is probable he may have
 had neither the  opportunity nor the   
capacity for exact observation4    ,the 
more carefully we sift the accounts     
which have been preserved of  great     
volcanic outbursts1 the more are we     
struck by the fact that the  appearances
 described can be resolved into a few   
simple operations1 the  true character  
of which has been distorted or disguised
 by the want of  accurate observation on
 the part of the witnesses4             
,sidenote3 ,,similarity ,,of ,,feeble   

,,and ,,violent ,,eruptions4    ,we are 
thus led to the conclusion that the     
grand and terrible  appearances         
displayed at ,vesuvius and other        
volcanoes in a state of  violent        
eruption do not differ in any essential 
respect from the  phenomena which we    
have witnessed accompanying the         
miniature outbursts  of ,stromboli4 ,and
 we are convinced1 by the same          
considerations1 that  the forces which  
give rise to the feeble displays in the 
latter case  would produce1 if acting   
with greater intensity and violence1 all
 the  magnificent spectacles presented  
in the former4    ,in ,vesuvius and     
,stromboli alike1 the active cause of   
all the phenomena  exhibited is found to
 be the escape of steam from the midst  
of  masses of incandescent liquefied    
rock4 ,the violence1 and therefore  the 
grandeur and destructive effects of an  
eruption1 depend upon the  abundance and
 tension of this escaping steam4        
,there is one respect in which volcanic 

phenomena are especially  calculated to 
excite the fear and wonder of           
beholders--namely1 in the  sudden and   
apparently spontaneous character of     
their manifestations4  ,eclipses were   
regarded as equally portentous with     
volcanic eruptions  till astronomers    
learned not only to explain the causes  
which gave  rise to them1 but even to   
predict to the second the times of their
  occurrence4 ,if we were able in like  
manner to warn the inhabitants of       
volcanic regions of the approach of a   
grand eruption1 the fear and            
superstition with which these events are
 now regarded would doubtless  be in    
great part dispelled4 ,the power of     
prediction is alike the  crucial test   
and the crowning triumph of a scientific
 theory4    ,but1 although natural      
philosophers are able to assign the     
causes to  which the grand operations of
 volcanoes are due1 and also to explain 
all the varied appearances which        
accompany them1 they have not as yet  so

 far mastered the laws which govern     
volcanic action as to be able to        
predict the periods of their            
manifestation4    ,that these           
operations1 like all others going on    
upon the globe1 are  governed by great  
natural laws we cannot for a moment     
doubt4 ,and that1  in all probability1  
more careful and exact observation and  
reasoning  will at some future time lead
 us to the recognition of these laws1   
every student of nature is sanguine4    
,but at the present time1 it must  be   
confessed1 we are very far indeed from  
being able to afford that  crowning     
proof of the truth of our theories of   
volcanic action which is  implied in the
 power of predicting the period and     
degree of intensity  of their           
manifestations4    ,sidenote3           
,,eruptions ,,and ,,the ,,intervals     
,,between ,,them4    ,there are1        
however1 some observations which lead us
 to hope that the  time may not be far  
distant when we shall have so ,eur      

obtained a  knowledge of the conditions 
on which volcanic action depends as to  
be  able to form some judgment as to its
 manifestations in the future at  any   
particular locality4 ,but we must       
recollect that these conditions  axe    
very numerous and complicated1 and that 
some of them may lie almost  entirely   
outside our sphere of observation2 hence
 hasty attempts in  this direction1 such
 as have recently been made1 are to be  
deprecated  by every true lover of      
science4    ,concerning the eruptions   
that have taken place at those volcanic 
centres which have been known from a    
remote antiquity1 we have records  from 
which we can determine the intervals    
separating these outbursts  and their   
relative violence4 ,a critical          
examination of these records  leads to  
the following conclusions3--    7#a47 ,a
 long period of quiescence is generally 
followed by an eruption  which is either
 of long duration or of great violence4 
7#b47 ,a long-continued1 or very violent

 eruption is usually followed by  a     
prolonged period of repose4    7#c47    
,feeble and short eruptions usually     
succeed one another at brief  intervals4
    7#d47 ,as a general rule1 the       
violence of a great eruption is         
inversely  proportional to its duration4
    ,it will be seen that these general 
conclusions are in perfect harmony  with
 the theory that volcanic outbursts are 
due to the accumulation  of steam at    
volcanic centres1 and that the tension  
of this imprisoned  gas eventually      
overcomes the repressing forces which   
tend to prevent  its manifestation4     
,before astronomers had learnt to       
determine all  the conditions on which  
the production of eclipses depends1 they
 had  found that these phenomena succeed
 one another at regular intervals4  ,the
 discovery of such astronomical cycles  
was a great advance in our  knowledge of
 the heavenly bodies1 and in the same   
way the determination  of these general 
relations between the intensity and     

duration of  volcanic outbursts and the 
intervals of time which separate them   
may  be regarded as the first step      
towards the discovery of the laws which 
govern volcanic activity4    ,in the    
actual determination of the conditions  
upon which the occurrence  of volcanic  
eruptions depends1 it must be confessed1
 however1 that  very little has as yet  
been done4 ,this is in part due to the  
fact that  some at least of these       
conditions lie beyond the limits of     
direct  observation4 ,but it must also  
be admitted1 on the other hand1 that    
little has been as yet accomplished     
towards the careful and systematic      
observation of those phenomena which    
may1 and probably do1 exert an          
influence in bringing about volcanic    
outbursts4    ,sidenote3 ,,influence    
,,of ,,atmospheric ,,conditions4    ,in 
the ,lipari ,islands there has prevailed
 a belief1 from the very  earliest      
period of history1 that the feeble      
eruptions of ,stromboli  are in some way

 dependent upon the condition of the    
atmosphere4  ,these islands were known  
to the ancients as the olian ,isles1    
from  the fact that they were once ruled
 over by a king of the name of  olus4   
,it seems not improbable that olus was  
gifted with natural  powers of          
observation and reasoning far in advance
 of those of his  contemporaries4 ,a    
careful study of the vapour-cloud which 
covers  ,stromboli would certainly      
afford him information concerning the   
hygrometric condition of the atmosphere2
 the form and position  assumed by this 
vapour-cloud would be a no less perfect 
index of the  direction and force of the
 wind2 and1 if the popular belief be    
well  founded1 the frequence and        
violence of the explosions taking place 
from the crater would indicate the      
barometric pressure4 ,from these  data  
an acute observer would be able to issue
 'storm-warnings' and                   
weather-prognostics of considerable     
value4 ,in the vulgar mind1 the  idea of

 the prediction of natural events is    
closely bound up with that  of their    
production2 and the shrewd              
weather-prophet of ,lipari was  after   
his death raised to the rank of a god1  
and invested with the  sovereignty of   
the winds4    ,whether the popular idea 
that the outbursts of ,stromboli are    
regulated  by atmospheric conditions has
 any foundation is still open to grave  
doubt4 ,it seems to be certain1 however1
 that during autumn and winter  the more
 violent paroxysms of the volcano occur1
 and that in summer  the action which   
takes place is far more regular and     
equable4 ,it would  be of the greatest  
benefit to science if an observatory    
were erected  beside the crater of      
,stromboli1 where a careful record might
 be kept of  all atmospheric changes1   
and of the synchronous manifestations of
 the  volcanic forces4    ,a little     
consideration will show that it is a by 
no means unreasonable  supposition that 
variations in atmospheric pressure may  

exercise a very  important influence in 
bringing about volcanic outbursts4      
,changes in  the barometer to the extent
 of two inches within a very short      
period  are not uncommon occurrences4 ,a
 very simple calculation will show that 
the fall of the mercury in the barometer
 to the extent of two inches  indicates 
the removal of a weight of two millions 
of tons from each  square mile of the   
earth's surface where this change takes 
place4 ,now1  if we suppose1 as we have 
good ground for doing1 that under       
volcanic  areas vast quantities of      
superheated water are only prevented    
from  flashing into steam by the        
superincumbent pressure1 a relief of    
this  pressure to the extent of two     
millions of tons on every square mile   
could scarcely fail to produce very     
marked effects4 ,the way in which       
explosions in fiery coal-mines generally
 follow closely upon sudden  falls in   
the atmospheric pressure is now well    
known2 and coal-mine  explosions and    

volcanic outbursts have this in common1 
that both  result from the sudden and   
violent liberation of subterranean      
gases4  ,there are not a few apparently 
well-authenticated accounts of volcanic 
and earthquake phenomena following      
closely on peculiar atmospheric         
conditions1 and the whole question of   
the relation of the volcanic  forces to 
atmospheric pressure1 as ,spallanzani   
himself so long ago  pointed out1 is    
deserving of a most careful and rigorous
 investigation4    ,sidenote3 ,,supposed
 ,,tidal ,,effects4    ,there is one    
other consideration which has frequently
 been urged as  worthy of especial      
attention1 in dealing with the question 
of the  exciting causes of volcanic     
outbursts4 ,if volcanoes were1 as was at
 one  time almost universally supposed1 
in direct communication with a great    
central mass of liquefied materials1 or 
even if any large reservoirs  of such   
liquids existed beneath volcanic        
districts1 as others have  imagined1    

then the different mobility of the solid
 and liquid portions  of the earth's    
mass would give rise to tidal effects   
similar to those  occurring in the      
surface waters of the globe4 ,under such
 circumstances1  volcanic outbursts1    
like the tides1 would be determined by  
the relative  positions of the sun and  
moon to our globe4 ,it is certain1      
however1  that no very direct relation  
has yet been established between the    
lunar periods and those of volcanic     
outbursts1 though recent close          
observations upon the crater of         
,vesuvius1 by ,professor ,palmieri1 do  
seem to lend support to the view that   
such relations may exist4    ,at the    
present time1 therefore1 it must be     
admitted that vulcanologists  have only 
just commenced those series of exact and
 continuous  observations which are     
necessary to determine the conditions   
that  regulate the appearance of        
volcanic phenomena4 ,the study of the   
laws  of volcanic action is yet in its  

infancy4 ,but the establishment of      
observatories on ,vesuvius and ,etna #ah
 fall of promise for the future1  and   
when we consider the advances which have
 been made1 during the last  one hundred
 years1 in our knowledge of the true    
nature of volcanic  action1 we need not 
despair that the extension of the same  
methods  of inquiry will lead to equally
 important results concerning the       
conditions which determine and the laws 
which govern it4    ,in the meanwhile1  
it is no small gain to have established 
the fact that  volcanic phenomena1      
divested of all those wonderful         
attributes with  which superstition and 
the love of the marvellous have         
surrounded them1  are operations of     
nature obeying definite laws1 which laws
 we may hope  by careful observation and
 accurate reasoning to determine2 and   
that  the varied appearances1 presented 
alike in the grandest and feeblest      
outbursts1 can all be referred to one   
simple cause--namely1 the escape1  from 

the midst of masses of molten materials1
 of imprisoned steam or  water-gas4     
,,chapter ,,iii4    ,,the ,,products    
,,of ,,volcanic ,,action4      ,while   
,spallanzani was engaged in             
investigating the nature of the action  
going on at ,stromboli and other        
,italian volcanoes1 his contemporary    
,dolomieu was laying the foundation of  
another important branch of  vulcanology
 by studying the characters of the      
different materials of  which volcanoes 
are built up4 ,since the publication of 
,dolomieu's  admirable works on the     
rocks of the ,lipari and ,ponza         
,islands1 science  has advanced with    
prodigious strides4 ,the chemist has    
taught us how  to split up a rock into  
its constituent elements and to         
determine the  proportions of these to  
one another with mathematical precision2
 the  mineralogist has done much in the 
investigation of the characters and     
mode of origin of the crystalline       
minerals which occur in these rocks2    

and the microscopist has shown how the  
minute internal structure of  these     
rocks may be made clearly manifest4 ,we 
shall proceed to give a  sketch of the  
present state of knowledge obtained by  
these different  kinds of               
investigations1 concerning the materials
 which are ejected  from volcanic vents4
    ,the most abundant of the substances
 which are ejected from volcanoes  is   
steam or water-gas1 which1 as we have   
seen1 issues in prodigious  quantities  
during every eruption4 ,but with the    
steam a great number  of other volatile 
materials frequently make their         
appearance4 ,the  chief among these are 
the add gases known as hydrochloric     
acid1  sulphurous acid1 sulphuretted    
hydrogen1 carbonic add1 and boracic     
acid2  and with these acid gases there  
issue hydrogen1 nitrogen1 ammonia1  the 
volatile metals arsenic1 antimony1 and  
mercury1 and some other  substances4 ,in
 considering the nature of the products 
which issue from  volcanic fissures1 it 

must be remembered that many substances 
which  under ordinary circumstances do  
not exhibit marked volatility are       
nevertheless easily carried away in fine
 particles when a current of  steam is  
passed over them4 ,as we shall have to  
point out in the sequel1  different     
volatile substances have a tendency to  
make their appearance  at volcanic vents
 according as the intensity of the      
action going on  within it varies4      
,the volatile substances issuing from   
volcanic fissures at high  temperatures 
react upon one another1 and many new    
compounds are thus  formed4 ,we have    
already seen how1 by the action of      
sulphurous acid  and sulphuretted       
hydrogen on each other1 the sulphur so  
common in  volcanic districts has been  
separated and deposited4 ,the           
hydrochloric  acid acts very            
energetically on the rocks around the   
vents1 uniting  with the iron in them to
 form the yellow ferric-chloride4 ,the  
rocks  all round a volcanic vent are not

 unfrequently found coated with this    
yellow substance1 which is almost always
 mistaken by casual observers  for      
sulphur4 ,in many volcanoes the constant
 passage through the rocks  of the      
various acid gases has caused nearly the
 whole of the iron1  lime1 and alkaline 
materials of the rocks to be converted  
into soluble  compounds known as        
sulphates1 chlorides1 carbonates1 and   
borates2 and1  on the removal of these  
by the rain1 there remains a white1     
powdery  substance1 resembling chalk in 
outward appearance1 but composed of     
almost pure silica4 ,there are certain  
cases in which travellers have  visited 
volcanic islands where chemical action  
of this kind has gone on  to such an    
extent1 that they have been led to      
describe the islands as  composed       
entirely of chalk4    ,sidenote3 ,,gases
 ,,emitted ,,from ,,volcanoes4    ,some 
of the substances issuing from volcanic 
vents1 such as hydrogen  and            
sulphuretted hydrogen1 are inflammable1 

and when they issue at a  high          
temperature1 these gases burst into     
flame the moment that they  come into   
contact with the air4 ,hence1 when      
volcanic fissures axe  watched at night1
 faint lambent flames are frequently    
seen playing over  them1 and sometimes  
these flames are brilliantly coloured1  
through the  presence of small          
quantities of certain metallic oxides4  
,such volcanic  flames1 however1 are    
scarcely ever strongly luminous and1 as 
we have  already seen1 the red1 glowing 
light which is observed over volcanic   
mountains in eruption is due to quite   
another cause4 ,the study by the  aid of
 the spectroscope of the flames which   
issue from volcanic vents  promises to  
throw much new light on the rarer       
materials ejected by  volcanoes4        
,spectroscopic observations of this kind
 have already been  commenced by        
,janssen1 at ,stromboli and ,santorin4  
,some of the volatile substances issuing
 from volcanic vents1 are at  once      

deposited when they come in contact with
 the cool atmosphere1  others form new  
compounds with one another and the      
constituents of the  atmosphere1 while  
others again attack the materials of the
 surrounding  rocks and form fresh      
chemical compounds with some of their   
ingredients4  ,thus1 there are          
continually accumulating on the sides   
and lips of  volcanic fissures deposits 
of sulphates1 chlorides1 and borates of 
the alkalies and alkaline earths1 with  
sal-ammoniac1 sulphur1 and the  oxides  
and sulphides of certain metals4 ,the   
lips of the fissures from  which steam  
and acid gases issue in volcanoes are   
constantly seen to  be coated with      
yellow and reddish-brown incrustations1 
consisting of  mixtures1 in varying     
proportions1 of these different         
materials1 and  these sometimes assume  
the form of stalactites and pendent     
masses4    ,sidenote3 ,,deposits        
,,around ,,volcanic ,,vents4    ,some of
 these products of volcanic action are  

of considerable  commercial value4 ,at  
,vulcano regular chemical works have    
been  established in the crater of the  
volcano1 by an enterprising ,scotch     
firm1 a great number of workmen being   
engaged in collecting the  materials    
which are deposited around the fissures1
 and are renewed  by the volcanic action
 almost as soon as they are removed4 ,in
 fig4  #f1 ,i have given a sketch of    
this singular spot1 taken from the high 
ground of the neighbouring ,island of   
,lipari4 ,from the village at  the foot 
of the volcano1 where the workmen live1 
a zig-zag road has  been constructed    
leading up the side1 and down into the  
crater of  the volcano4 ,on this road1  
workmen and mules1 laden with the       
various  volcanic materials1 may be seen
 constantly passing up and down4        
,illustration3 ,fig4 #f4--,view of      
,vulcano1 with ,vulcanello in the       
foreground taken from the south end of  
the ,island of ,lipari4    ,vulcano     
appears to have been frequently in a    

state of violent eruption  during the   
past #b1jjj years--the last great       
outburst having taken place  in #aghf4  
,in #ahgc the activity in the crater of 
,vulcano suddenly became  more          
pronounced in character1 and the workmen
 hastened to escape from  the dangerous 
spot1 but1 before they could do so1     
several of them  were severely injured  
by the explosions4 ,after this outburst1
 which  did not prove to be of very     
violent character1 the quantity of gases
  issuing from the fissures in the      
crater was for a time much greater  than
 before1 and the productiveness of these
 great natural chemical  works was      
proportionately increased3 but          
eventually the action died out  almost  
entirely4 ,the chief products of        
,vulcano which are of commercial  value1
 are sal-ammoniac1 sulphur1 and boracic 
acid4 ,at one time it was  even         
contemplated that great leaden chambers 
should be erected over the  principal   
fissures at the bottom of the crater of 

,vulcano1 in which  chambers the        
volatile materials might be condensed   
and collected4 ,the  change in the      
condition of the volcano has            
unfortunately prevented the  carrying   
out of this bold project4    ,besides   
the volatile substances which issue from
 volcanic vents1  mingling with the     
atmosphere or condensing upon their     
sides1 there are  also many solid       
materials ejected1 and these may        
accumulate around the  orifices1 till   
they build up mountains of vast         
dimensions1 like ,etna1  ,teneriffe1 and
 ,chimborazo4 ,some of these solid      
materials are evidently  fragments of   
the rock-masses1 through which the      
volcanic fissure has  been rent2 these  
fragments have been carried upwards by  
the force of  the steam-blast and       
scattered over the sides of the volcano4
 ,but the  principal portion of the     
solid materials ejected from volcanic   
orifices  consists of matter which has  
been extruded from sources far beneath  

the  surface1 in a highly-heated and    
fluid or semi-fluid condition4          
,sidenote3 ,,ejected ,,rock-,,fragments4
    ,the fragments torn from the sides  
of volcanic fissures consist of the     
rocks through which the eruptive forces 
may happen to have opened their  way2   
pieces of sandstone1 limestone1 slate1  
granite1 c41 are thus  frequently found 
in considerable numbers among materials 
which build up  volcanic mountains4     
,thus1 some of the volcanic cones in the
 ,eifel are  very largely made up of    
fragments of slate1 which have been torn
 from  the sides of the vents by the    
uprushing currents of steam4 ,at        
,vesuvius  masses of limestone are      
frequently ejected1 and may be picked up
 all  over the slopes of the mountains4 
,these limestone-fragments frequently   
contain fossils1 and ,professor         
,guiscardi1 of ,naples1 has been able to
  collect several hundred species of    
shells1 transported thus by volcanic    
action from the rock-masses which form  

the foundation of the volcano  of       
,vesuvius4 ,the action of water at a    
high temperature1 and under  such       
enormous pressure as must exist beneath 
volcanic mountains1 has  often produced 
changes in the rocks of which fragments 
are ejected  from volcanic vents4 ,the  
so-called 'lava' ornaments1 which are so
  extensively sold at ,naples1 are not  
made from the materials to which        
geologists apply that name1 but from the
 fragments of altered limestone  that   
have been torn from the rocks beneath   
the mountain1 and scattered  by the     
eruptive forces all over its sides4 ,the
 chemical action of the  superheated and
 highly-compressed steam on the rocks   
beneath volcanoes  frequently results in
 the formation of beautifully           
crystallised  minerals4 ,such           
crystallised minerals abound in the     
rock-fragments  scattered over the sides
 of ,vesuvius and other volcanoes1 both 
active  and extinct4 ,they have been    
formed in the great chemical            

laboratories  which exist beneath the   
volcano1 and have been brought to the   
surface  by the action of the steam-jets
 issuing from its fissures4    ,of still
 greater interest are those materials   
which issue from volcanic  orifices in  
an incandescent1 and often in a molten1 
condition1 and  which are evidently     
derived from sources far below the      
earth's surface4  ,it is to these       
materials that the name of 'lavas' is   
properly applied4    ,lavas present a   
general resemblance to the slags and    
clinkers which  are formed in our       
furnaces and brick-kilns1 and consist1  
like them1 of  various stony substances 
which have been more or less perfectly  
fused4  ,when we come to study the      
chemical composition and the            
microscopical  structure of lavas1      
however1 we shall find that there are   
many respects  in which they differ     
entirely from these artificial products4
    ,let us first consider the facts    
which are taught us concerning the      

nature and origin of lavas1 by a        
chemical analysis of them4    ,sidenote3
 ,,chemical ,,composition ,,of ,,lavas4 
,of the sixty-five or seventy chemical  
elements1 only a very small  number     
occur at all commonly in lavas4 ,eight  
elements1 indeed1 make  up the great    
mass of all lavas--these are oxygen1    
silicon1 aluminium1  magnesium1 calcium1
 iron1 sodium1 and potassium4 ,but even 
these  eight elements are present in    
very unequal proportions4 ,oxygen makes 
up nearly one-half the weight of all    
lavas4 ,almost all the other  elements  
found in lavas exist in combination with
 oxygen1 so that  lavas consist entirely
 of what chemists call 'oxides4' ,this  
is a most  remarkable circumstance1     
which1 as we shall presently see1 is of 
great  significance4 ,the metalloid     
silicon makes up about one-fourth of the
  weight of most lavas1 and the metal   
aluminium about one-tenth4 ,the  other  
five elements vary greatly in their     
relative proportions in  different      

lavas4    ,in all lavas the substance   
which forms the greatest part of the    
mass  is the compound of oxygen and     
silicon1 known as silica or silicic     
acid4 ,in its pure form1 this substance 
is familiar to us as quartz1 or         
rock-crystal and flint4 ,silica is      
present in all lavas in proportions     
which vary from one-half to four-fifths 
of the whole mass4 ,now1 this           
substance1 silica1 has the property of  
forming more complex compounds  by      
uniting with the other oxides present in
 lavas--namely1 the oxides  of          
aluminium1 magnesium1 calcium1 iron1    
potassium1 and sodium4 ,silica  is      
called by chemists an acid1 the other   
oxides in lavas are termed  bases1 and  
the compounds of silica with the bases  
are known as  silicates4 ,hence we see  
that lavas are composed of a number of  
different silicates--the silicates of   
aluminium1 magnesium1 calcium1  iron1   
potassium1 and sodium4    ,the above    
statements will perhaps be made clearer 

by the accompanying  table from which it
 will be seen that lavas are compounds  
in varying  proportions of six kinds of 
salts--namely1 the silicates of alumina1
  magnesia1 lime1 iron1 potash1 and     
soda4    ,composition of ,lavas4        
,elements   ,binary ,compounds          
,salts                         ,acid    
,bases       ,silicon         ,silica-- 
,o  ,aluminum                --,alumina 
,silicate of ,alumina    x              
y  ,magnesium               --,magnesia 
,magnesia    g                          
e  ,calcium                 --,lime     
,lime    n                              
,iron                    --,iron        
,iron                                   
,potassium               --,potash      
,potash                                 
,sodium                  --,soda        
,soda      ,now1 in some lavas the acid 
constituent1 or silica1 is present in   
much  larger proportions than in others4
 ,those lavas with a large proportion   
of silica are called 'acid lavas1' those

 with a lower percentage of  silica1 and
 therefore a higher proportion of the   
bases1 are known as  the 'basic lavas4' 
,it is convenient to employ the term    
'intermediate  lavas' for those in which
 the proportion of silica is lower than 
in the  acid lavas1 and the proportion  
of the bases is lower than in the basic 
lavas4    ,the acid lavas contain from  
#ff to #hj per cent1 of silica2 they are
 poor  in lime1 magnesia1 and oxide of  
iron1 but rich in potash and soda4 ,the 
basic lavas contain from #de to #ee per 
cent1 of silica2 they are rich in       
magnesia1 lime1 and oxide of iron1 but  
poor in soda and potash4 ,in the        
intermediate lavas the proportion of    
silica varies from #ee to #ff per  cent4
    ,as the basic-lavas contain a larger
 proportion of oxide of iron and  other 
heavy oxides than the acid-lavas1 the   
former have usually a  higher specific  
gravity than the latter2 it is1 indeed1 
possible in  most cases to distinguish  
between these different varieties by    

simply  weighing them in water and in   
air4    ,sidenote3 ,,different ,,kinds  
,,of ,,lava4    ,the basic lavas are    
usually of much darker colour than the  
add  lavas--the terms acid lavas1       
intermediate lavas1 and basic lavas     
correspond indeed pretty closely with   
the names trachytes1 greystones  and    
basalt1 which were given to the         
varieties of lavas by the older  writers
 on volcanoes1 at a time when their     
chemical constitution had  not been     
accurately studied4 ,fresh lavas of acid
 composition are  usually nearly white  
in colour1 intermediate lavas are of    
various  tints of grey1 and basic lavas 
nearly black4 ,it must be remembered1   
however1 that colour is one of the least
 persistent1 and therefore  one of the  
least valuable1 characters by means of  
which rocks can  be discriminated1 and  
also that by exposure to the influence  
of the  atmospheric moisture the iron   
present in all lavas is affected1 and   
the lavas belonging to all classes1 when

 weathered1 assume reddish and          
reddish-brown tints4    ,geologists have
 devised a great number of names for the
 various kinds  of lava which have been 
found occurring round volcanic vents in 
different parts of the world1 and the   
study of these varieties is full  of    
interest4 ,for our present purpose1     
however1 it will be sufficient  to state
 that they nearly all fall into five    
great groups1 known as  the ,rhyolites1 
the ,trachytes1 the ,andesites1 the     
,phonolites1 and the  ,basalts4 ,the    
,rhyolites are acid lavas1 the ,basalts 
are basic lavas1  and the ,trachytes1   
,andesites1 and ,phonolites1 different  
kinds of  intermediate lavas1           
distinguished by the particular minerals
 which they  contain4    ,before we part
 from this subject of the classification
 of lavas  according to their chemical  
composition1 it will be well to point   
out that there exists a small group of  
lavas which stand quite by  themselves1 
and cannot be referred to either of the 

classes we have  indicated4 ,they       
contain a smaller proportion of silica1 
and a much  larger proportion of        
magnesia and oxide of iron than the     
other lavas1  and may be made to        
constitute a small sub-group1 to which  
we may apply  the term of 'ultra-basic  
lavas4' ,although much less widely      
distributed  than the other varieties1  
they are1 in some respects1 as we shall 
presently have to point out1 of far     
greater interest to the geologist  than 
all the other kinds of lavas4           
,sidenote3 ,,minute ,,structure ,,of    
,,lavas4    ,we will now proceed to     
consider the facts which are brought to 
light  concerning the nature of lavas1  
when they are studied by the aid  of the
 microscope4 ,although most lavas appear
 at first sight to be  opaque           
substances1 yet it is easy to prepare   
slices of them which are  sufficiently  
thin to transmit light4 ,in such thin   
transparent slices  we are able to make 
out1 by the aid of the microscope1      

certain very  interesting details of    
structure1 which afford new and         
important  evidence bearing on the mode 
of origin of these rocks4    ,host lavas
 are capable of being melted by the heat
 of our furnaces2  but the different    
kinds of lava vary greatly in the degree
 of their  fusibility4 ,the basic lavas1
 or those with the smallest proportion  
of  silica1 are usually much more easily
 fusible than those which contain a     
high percentage of silica1 the add      
lavas4    ,now1 it is a very noteworthy 
circumstance1 that when a lava is       
artificially fused it assumes on cooling
 very different physical  characters to 
those which were presented by the       
original rock4    ,if we examine the    
freshly-broken surface of a piece of    
lava1 we  shall1 in most cases1 find    
that it contains a great number of those
  regular-shaped bodies which we call   
crystals2 in some cases these  crystals 
are so small as to be scarcely visible  
to the naked eye1 in  others they may be

 an inch or more in length4 ,most lavas 
are thus seen  to be largely made up of 
crystals of different minerals4 ,the    
minerals  which are usually contained in
 lavas are quartz1 the various kinds of 
felspar1 augite1 hornblende1 the        
different kinds of mica1 olivine1 and   
magnetite4    ,but when a piece of lava 
is melted in a furnace1 all these       
crystalline  minerals disappear1 and the
 resulting product is the homogeneous   
substance which we call glass4 ,if1 as  
many suppose1 lavas acquire the         
fluidity which they possess when issuing
 from volcanic vents as the  result of  
simple fusion it is strange that        
artificially fused lavas do  not agree  
more closely in character with the      
natural products4    ,a careful         
examination of different kinds of lavas1
 however1 will  show that they vary very
 greatly in character among themselves4 
,some  lavas are as perfectly glassy in 
structure as those which have been      
artificially fused1 while others contain

 great numbers of crystals1  which may  
sometimes be of very large size4    ,if 
we prepare thin transparent slices of   
these different kinds of  lavas1 and    
examine them by the aid of the          
microscope1 we shall find  that lavas   
are made up of two kinds of materials1 a
 base or groundmass  of a glassy        
character1 and distinct crystals of     
different minerals1  which are          
irregularly distributed through this    
glassy base1 like the  raisins1         
currants1 and pieces of candied peel in 
a cake4 ,in some  cases the glassy base 
makes up the whole mass of the rock2 in 
others1  smaller or larger numbers of   
crystals are seen to be scattered       
through  a glassy base2 while in others 
again the crystals are so numerous that 
the presence of an intervening glassy   
base or groundmass can only be  detected
 by the aid of the microscope4          
,sidenote3 ,,study ,,of ,,lavas ,,with  
,,the ,,microscope4    ,if thin slices  
of the glassy materials of lavas be     

examined with high  magnifying powers1  
new and interesting facts are revealed4 
,through  the midst of the clear glassy 
substance cloudy patches are seen to be 
diffused2 and1 if we examine them with a
 still higher power1 these  cloudy      
patches resolve themselves into         
innumerable particles1 some  transparent
 and others opaque1 having very definite
 outlines4 ,at the  same time fresh     
cloudy patches are brought into view1   
which can only  be resolved by yet      
higher powers of the microscope4 ,in    
examining these  natural glasses by the 
aid of the microscope1 we are forcibly  
reminded  of what occurs when the       
',milky ,way' and some other parts of   
the heavens  are studied with a         
telescope4 ,as the power of the         
instrument is  increased the nebulous   
patches are resolved into distinct      
stars1 but  fresh nebulous masses come  
into view1 which are in turn resolved   
into  stars1 when higher powers of the  
instrument are employed4    ,in the     

,frontispiece1 ,no4 #a illustrates the  
appearance presented by  these volcanic 
glasses when examined with a high power 
of a microscope4  ,through a glassy base
 is seen a number of diffused nebulous  
patches1  which are in places resolved  
into definite particles4    ,these      
minute particles of definite form1 which
 the microscope has  revealed in the    
midst of the glassy portions of lava1   
have received the  name of microliths1  
or crystallites4 ,the study of the      
characters and  mode of arrangement of  
these microliths or crystallites has in 
recent  years thrown much new light on  
the interesting problems presented by   
lavas4    ,in some glassy lavas the     
microliths or crystallites1 instead of  
being  indiscriminately diffused through
 the mass of the base or groundmass1    
are found to be collected together into 
groups of very definite form4  ,in ,no4 
#b of the ,frontispiece we have a       
section of a glassy rock in  which the  
crystallites have united together1 so as

 to build up groups  presenting the most
 striking resemblance to fronds of      
ferns4 ,around  these groups spaces of  
dear glass have been left by the        
gathering up  of the crystallites1 which
 in other parts of the mass are seen to 
be  equally diffused through it4 ,in    
this formation of groups of microliths  
we cannot but recognise the action of   
those crystalline forces1 which  on     
frosty mornings cover our windows with a
 mimic vegetation composed  of icy      
particles4    ,in other cases1 again1   
the crystallites scattered through the  
glassy  portions of lavas unite in      
radial groups about certain centres1 and
  thus build up globular masses to which
 the name of 'sphrulites' has  been     
given4 ,no4 #c in the ,frontispiece     
illustrates the formation of  these     
sphrulites4    ,now1 a careful study of 
the microliths or crystallites has      
proved that  they are the minute        
elements of which those wonderfully     
beautiful  objects which we call        

crystals are built up4 ,in some cases we
 can  see that the crystallites are     
becoming united together in positions   
determined by mathematical laws1 and the
 group is gradually assuming  the       
outward form and internal structure of a
 crystal4 ,in other cases  crystals may 
be found which are undergoing a         
disintegrating action1  and are then    
seen to be made up of minute elements   
similar to the  crystallites or         
microliths of glassy rocks4             
,sidenote3 ,,crystallites ,,and         
,,crystals4    ,the conclusion is       
confirmed by the fact that if we take an
 artificially  fused lava and allow it  
to cool slowly1 it will be found that   
the  glassy mass into which it has      
resolved itself contains numerous       
crystallites4 ,if the cooling process be
 still further prolonged1 these         
crystallites will be found to have      
united themselves into definite  groups1
 and sometimes distinct crystals are    
formed in the mass2 under  these        

circumstances the rock frequently loses 
its glassy appearance and  assumes a    
stony character4    ,in connection with 
this subject1 it may be mentioned that  
some years  ago a very ingenious        
invention was submitted to trial in the 
,works  of the ,messrs4 ,chance1 of     
,birmingham4 ,it had been suggested that
 if  certain lavas of easy fusibility   
were melted and poured into moulds1  we 
might thus obtain elaborately ornamented
 stone-work1 composed of  the hardest   
material1 without the labour of the     
mason4 ,the molten rock  when quickly   
cooled was found to assume the form of a
 black glass1 but  when very slowly     
cooled passed into a stony material4    
,unfortunately1  it was found that this 
material did not withstand the weather  
like  ordinary building stones1 and1 in 
consequence1 the manufacture had to  be 
abandoned4    ,now1 the study of the    
products of volcanoes has led geologists
 to  recognise the true relations       
between glassy and crystalline rocks4   

,in the amorphous mixture of various    
silicates which compose a glass1        
chemical affinity causes the separation 
of certain portions of  definite        
composition1 and these form the         
microliths or elements of  which        
different crystalline minerals are built
 up4 ,under the influence  of the       
crystalline forces1 there is a great    
shaking or agitation in  the mass1 and  
the microliths of similar kind come     
together and become  united1 like the   
fragments in ,ezekiel's valley of dry   
bones4    ,although we cannot see this  
process taking place under our eyes1  in
 a mass of lava1 yet we may study       
specimens in which the action  has been 
arrested in its different stages4 ,in   
order to understand  the development of 
an acorn into an oak-tree1 it is not    
necessary  to watch the whole series of 
changes in a particular case4 ,a visit  
to an oak-thicket1 in which             
illustrations of every stage of the     
transformation may be found1 will afford

 us equally certain information  on the 
subject4    ,in the same way by the     
examination of such a series of         
rock-sections  as that represented in   
the ,frontispiece1 we may understand    
how1 in the  midst of a mass of mixed   
silicates constituting a natural glass1 
the  separation of microliths takes     
place2 these unite into groups which are
  the skeletons of crystals1 and        
finally1 by the filling up of the empty 
spaces in these skeletons1 complete     
crystals are built up4 ,the series  of  
operations may1 however1 be interrupted 
at any stage1 and this stage  we may    
have the chance of studying4            
,sidenote3 ,,glassy ,,and ,,crystalline 
,,lavas4    ,we are able1 as we shall   
show in a future chapter1 to examine    
many  rock-masses that have evidently   
formed the reservoirs from which        
volcanoes have been supplied1 and others
 that fill up the ducts which           
constituted the means of communication  
between these subterranean  reservoirs1 

and the surface of the earth4 ,now in   
these subterranean  regions the lavas   
have been placed under conditions       
especially  favourable for the action of
 the crystalline forces--they must have 
cooled with extreme slowness1 and they  
must have been under an enormous        
pressure1 produced in part by the weight
 of the superincumbent rocks1  and in   
part by the expansive force of the      
imprisoned steam4 ,we are not1          
therefore1 surprised to find that in    
these subterranean regions1 the  lavas1 
while retaining the same chemical       
composition1 have assumed a  much more  
perfectly crystalline condition4 ,in    
some cases1 indeed1 the  whole rock has 
become a mass of crystals without any   
base or groundmass  at all4    ,an      
examination of the ,frontispiece will   
illustrate this perfect  gradation from 
the glassy to the crystalline condition 
of lavas4 ,no4  #a represents a glass   
through which microliths or crystallites
 of  different dimensions and character 

are diffused4 ,in ,nos4 #b and #c1      
these crystallites have united to form  
regular groups4 ,in ,no4 #d1 which  may 
be taken as typical of the features     
presented by most lavas1 we  have a     
glassy groundmass containing microliths 
7a 'crypto-crystalline  base'71 through 
which distinct crystals are distributed4
 ,nos4 #e and #f  illustrate the        
characters presented by lavas which have
 consolidated  at considerable depths   
beneath the surface2 in the former we   
have  a mans of small crystals 7a       
'micro-crystalline base'7 with larger   
crystals scattered through it2 while the
 latter is entirely made up of  large   
crystals without any trace of a base or 
groundmass4    ,now1 as all lavas are   
found sometimes assuming the glassy     
condition at  the surface1 so when seen 
in the masses which have consolidated   
with  extreme slowness1 and under great 
pressure1 in subterranean regions1  the 
same materials are found in the         
condition of a rock which is built  up  

entirely of crystals4 ,chemists have    
found that artificial mixtures  of      
silicates in which soda and potash are  
present in considerable  quantities1    
have a great tendency to assume the     
glassy condition on  cooling from a     
state of fusion1 and glass manufacturers
 are always  careful to use considerable
 proportions of the alkalis as          
ingredients1  in making glass4 ,it is   
found1 in like manner1 that those lavas 
which  contain the largest portion of   
the silicates of soda and potash 7the   
'acid lavas'7 most frequently assume the
 condition of a natural glass4          
,geologists have given distinct names to
 the glassy and the perfectly           
crystalline conditions of the different 
kinds of lavas1 the glassy  varieties   
being found in masses which have cooled 
rapidly near the  surface1 and the      
crystalline varieties in masses which   
have cooled  slowly at great depths4    
,the names of these two conditions of   
the five  great classes into which we   

have divided lavas are as follows3--    
,sidenote3 ,,highly ,,crystalline       
,,igneous ,,rocks4        ,crystalline  
,forms4     ,lavas4    ,glassy ,forms4  
,granite                 ,rhyolite      
,syenite                 ,trachyte      
,obsidian4    ,diorite                  
,andesite      ,miascite                
,phonolite     ,gabbro                  
,basalt                   ,tachylyte4   
,as vitreous rocks have little in their 
general appearance to  distinguish them 
from one another1 the glassy forms of   
the first  four classes of lava have not
 hitherto received distinct names1 but  
have been confounded together under the 
name of obsidian4 ,if we  determine the 
specific gravities of rocks having the  
same composition  but different         
structures1 we shall find that they     
become heavier in  proportion as the    
crystalline structure is developed in   
them4 ,thus  gabbro is heavier1 but     
tachylyte is lighter than basalt1 bulk  
for bulk1  though all have the same     

chemical composition4    ,nor are the   
crystals contained in lavas less worthy 
of careful study1  by the aid of the    
microscope1 than the more or less glassy
 groundmass  in which they are embedded4
 ,mr4 ,sorby has shown that the crystals
 found  in lavas1 exhibit many          
interesting points of difference from   
those  which separate out in the midst  
of a mass of the same rock1 when it has 
been artificially melted and slowly     
cooled4 ,there are other facts which    
also point to the conclusion that1 while
 the glassy groundmass of lavas  may    
have been formed by cooling from a state
 of fusion1 the larger and  well-formed 
crystals in these lavas must have been  
formed under other  and very different  
conditions4    ,the larger crystals in  
lavas exhibit evidence of having been   
slowly  built up in the midst of a      
glassy mass1 containing crystallites and
  small crystals4 ,we can frequently    
detect evidence of the interruptions    
which have occurred in the growth of    

these crystals in the concentric  zones 
of different colour or texture which    
they exhibit2 and portions  of the      
glassy base or groundmass are often     
found to have been caught up  and       
enclosed in these crystals during their 
growth4    ,but when we find1 as in the 
porphyritic pitchstones1 a glassy base  
containing only minute crystallites1    
through which large and perfectly       
formed crystals are distributed1 we can 
scarcely doubt that the minute          
crystallites and the larger crystals    
have separated from the base under  very
 different conditions4 ,this is         
indicated by the bet that we detect  in 
these cases no connecting links between 
the embryo microliths and  the perfect  
crystals2 and a confirmation of the     
conclusion is seen in  the circumstance 
that many of the crystals are found to  
have suffered  injury as if from        
transport1 their edges and angles being 
rounded and  abraded1 and portions being
 occasionally broken off from them4     

,hence we are led to conclude that the  
larger crystals in lavas were  probably 
separated from the amorphous mass in the
 subterranean  reservoirs beneath the   
volcano1 and were carried up to the     
surface in  the midst of the liquefied  
glassy material which forms the         
groundmass  of lavas4 ,when we come to  
examine these crystals more closely1 we 
find  that certain very curious         
phenomena are exhibited by them which   
lend  powerful support to this          
conclusion4    ,illustration3 ,fig4     
#g4--,minute ,cavities1 containing      
,liquids1 in the  ,crystals of ,rocks4  
,sidenote3 ,,liquid ,,cavities ,,in     
,,crystals4    ,it is found convenient  
by geologists to designate those rocks  
which  have consolidated in deep-seated 
portions of the earth's crust  as       
,platonic ,rocks1 confining the name of 
,volcanic rocks to those  consolidating 
,at the surface2 but ,plutonic and      
,volcanic ,rocks shade  into one another
 by the most insensible gradations4     

,when the crystals embedded in granitic 
rocks1 and in some lavas1 are  examined 
with the higher powers of the           
microscope1 they are frequently  seen to
 contain great numbers of excessively   
minute cavities4 ,each of  these        
cavities resembles a small spirit-level1
 having a quantity of  liquid and a     
bubble of gas within it4 ,in fig4 #g we 
have given a series  of drawings of     
these cavities in crystals as seen under
 a high power  of the microscope4 ,in   
,no4 #a a group of such cavities is     
represented1  one of which is full of   
liquid1 while two others are quite      
empty2 the  remaining cavities all      
contain a liquid with a moving bubble of
 gas4  ,in ,no4 #b two larger cavities  
are shown1 containing a liquid and a    
bubble of gas2 and it will be seen from 
these how varied in form these  cavities
 sometimes are4 ,in ,nos4 #c1 #d and #f 
the liquid in the cavities  contains1   
besides the bubbles1 several1 minute    
crystals2 and in ,no4 #f  we have a     

cavity containing two liquids and a     
bubble4    ,in the largest of such      
cavities the bubble is seen to change   
its  place so as always to lie at the   
upper side of the cavity1 when the      
position of the latter is altered1 just 
as in a spirit-level4 ,but in  the      
smallest cavities the bubbles appear to 
be endowed with a power of  spontaneous 
movement2 like imprisoned creatures     
trying to escape1 these  bubbles are    
seen continually oscillating from side  
to side and from end  to end of the     
cavities which enclose them4 ,in fig4 #h
 a minute cavity  containing a liquid   
and bubble is shown1 the path pursued by
 the latter  in its wonderful gyrations 
being indicated by the dark line4 ,these
  cavities are exceedingly minute1 and  
so numerous that in some crystals  there
 must be millions of them present2      
indeed1 in certain cases1 as  we        
increase the magnifying power of our    
microscopes1 new and smaller  cavities  
continually become visible4 ,it has been

 estimated that in some  instances the  
number of these minute liquid-cavities  
in the crystals of  rocks amounts to    
from one thousand millions to ten       
thousand millions in  a cubic inch of   
space4    ,illustration3 ,fig4          
#h--,minute ,liquid-cavity in a         
,crystal1 with a moving  ,bubble4 7,the 
path of the bubble is indicated by the  
dark line47    ,sidenote3 ,,nature ,,of 
,,liquids ,,in ,,cavities4    ,what is  
the nature of the liquids which are thus
 imprisoned in these  cavities contained
 in the crystals of lavas and granites8 
,careful  experiments have given a      
conclusive answer to this question4 ,in 
many  cases the liquid is water1 usually
 containing considerable quantities  of 
saline matter dissolved in it4          
,sometimes the saline matters are       
present in such abundance that they     
cannot all pass into solution1 but      
crystallise out1 as in fig4 #g--,nos4   
#c1 #d1 #e--where cubic crystals of  the
 chlorides of sodium and potassium are  

seen floating in the liquid2  in other  
cases the liquid is a hydrocarbon like  
the mineral oil which  is present in    
great abundance in deep-seated rocks in 
many parts of the  globe4 ,but in some  
other cases the liquid contained in the 
cavities  of crystals is found to be one
 which could scarcely be anticipated  to
 occur under such circumstances--the gas
 known as carbonic add1  which under    
extreme pressure can be reduced to a    
liquid condition4 ,in  cavities         
containing liquefied carbonic acid1 if  
the rock be warmed up  to #hf or #ij    
,fahrenheit the bubble suddenly         
vanishes1 sometimes with  an appearance 
like ebullition or boiling1 as          
represented in fig4 #i4  ,now the       
temperature which we have indicated is  
the 'critical point' of  carbonic acid1 
and above that temperature it cannot    
exist in a liquid  condition1 however   
great may be the pressure to which it is
 subjected4  ,the liquid has been       
converted into a gas which completely   

fills the  cavity4 ,the carbonic acid in
 the cavities of crystals has frequently
  been isolated and its nature placed   
beyond doubt by spectroscopic and       
ordinary chemical tests4    ,the        
presence of these liquids in the        
cavities of crystals clearly  proves    
that the latter must have been formed   
under enormous pressure--a  pressure    
sufficiently great to reduce1 not only  
steam1 but also  volatile hydrocarbons  
and even gaseous carbonic acid1 to the  
bulk of a  liquid4    ,illustration3    
,fig4 #i4--;,cavity in ,crystal         
containing ,carbonic-,acid ,gas  at a   
temperature of #hf ,f41 and passing from
 the liquid to the gaseous  condition4  
,such conditions of enormous pressure we
 may infer to exist in the  deep-seated 
reservoirs beneath volcanoes1 where1    
besides the weight  of the              
superincumbent rock-masses1 we have the 
compressing force of  great quantities  
of elastic vapour held in confinement4  
,the crystals of  which granitic rocks  

are entirely built up exhibit clear     
evidence of  having been all formed     
under these conditions of enormous      
pressure4 ,the  glassy base or          
groundmass of lavas1 on the other hand1 
presents all the  characters of         
materials that have cooled from a state 
of fusion4 ,most  lavas consist in part 
of crystals1 exhibiting fluid-cavities  
like those  present in granite1 and in  
part of a base1 which has evidently been
  formed by the cooling of a fused mass4
 ,we are therefore justified in         
concluding that the crystals have been  
formed in subterranean recesses1  and   
that the groundmass or base has         
consolidated at the surface4 ,the       
bearing of these conclusions upon some  
of the great problems presented  by     
volcanoes we shall have occasion to     
point out in the sequel4    ,sidenote3  
,,cause ,,of ,,movement ,,of ,,bubbles4 
,one of the most interesting inquiries  
suggested by the study of  the          
liquid-cavities in volcanic rocks is    

that of the cause of the  apparently    
spontaneous movement of the bubbles     
which we have described  as taking place
 in some of the smaller of them4 ,the   
ingenious  experiments of ,mr4 ,noel    
,hartley have suggested to ,professor   
,stokes  an explanation which is        
probably the true one4 ,it appears that 
these  minute globes of vapour are in   
such a state of unstable equilibrium as 
to be affected by the smallest changes  
of temperature1 and that the  variations
 in the heat of the atmosphere1 due to  
currents of air and  the movement of    
warm or cold bodies through it1 are     
sufficient to cause  the oscillation of 
these sensitively poised bubbles4       
,the short account which we have been   
able to give in the foregoing  pages of 
the researches that have been carried on
 concerning the nature  of the materials
 ejected from volcanoes will serve to   
show that these  investigations have    
already made known many facts of great  
interest1  and that the farther pursuit 

of them is full of the highest promise4 
,to the scientific worker no subject is 
too vast for his research1 no  object so
 minute as to be unworthy of his most   
patient study4 ,in some  of our future  
inquiries concerning the nature of      
volcanic action1 we  shall be led to an 
investigation of the phenomena displayed
 in the sun1  moon1 comets and other    
great bodies of the universe2 but       
another road  to truths of the same     
grandeur and importance is found1 as we 
have  seen1 in an examination of the    
mode of development of crystallites1 and
  a study of the materials contained in 
the microscopic cavities of the         
minutest crystals4          ,,chapter   
,,iv4    ,,the ,,distribution ,,of ,,the
 ,,materials ,,ejected ,,from ,,volcanic
 ,,vents4      ,the escape of great     
quantities of steam and other gases from
 the midst  of a mass of fluid or       
semi-fluid lava gives rise to the       
formation of  vast quantities of froth  
or foam upon its surface4 ,this froth or

 foam1  which is formed upon the surface
 of lava by the escape of gaseous       
matters from within it1 is made up of   
portions of the lava distended  into    
vesicles1 in the same way that bubbles  
are formed on the surface  of water4 ,it
 bears precisely the same relation to   
the liquid mass of  lava that the white 
crest of foam upon an advancing wave    
does to the  sea-water1 from the bubbles
 of which it is formed4    ,this froth  
upon the surface of lavas varies greatly
 in character  according to the nature  
of the material from which it is formed4
 ,in  the majority of cases the lavas   
consist1 as we have seen1 of a mass  of 
crystals floating in a liquid magma1 and
 the distension of such a  mass by the  
escape of steam from its midst gives    
rise to the formation  of the rough     
cindery-looking material to which the   
name of 'scoria'  is applied4 ,but when 
the lava contains no ready-formed       
crystals1 but  consists entirely of a   
glassy substance in a more or less      

perfect state  of fusion1 the liberation
 of steam gives rise to the formation of
 the  beautiful material known as       
'pumice4' ,pumice consists of a mass of 
minute glass bubbles2 these bubbles have
 not usually1 however1 retained  their  
globular form1 but have been elongated  
in one direction through  the movement  
of the mass while it was still in a     
plastic state4    ,the steam frequently 
escapes from lava with such violence    
that the  froth or scum on its surface  
is broken up and scattered in all       
directions1 as the foam crests of waves 
are dispersed by the wind  during a     
storm4 ,in this way fragments of scoria 
or pumice are often  thrown to the      
height of many hundreds or thousands of 
feet into the  atmosphere1 as we have   
seen is the case at ,stromboli and      
,vesuvius4  ,indeed1 during violent     
eruptions1 a continuous upward discharge
 of  these fragments is maintained1 the 
ragged cindery masses hurtling one      
another in the atmosphere1 as they are  

shot perpendicularly upwards  to an     
enormous height and fall back into the  
vent2 or they may rise  obliquely and   
describe curves so as to descend outside
 the orifice from  which they were      
ejected4    ,sidenote3 ,,fineness ,,of  
,,volcanic ,,dust4    ,during their     
upward discharge and downward fall1 the 
cindery fragments  are by attrition     
continually reduced to smaller          
dimensions4 ,the noise  made by these   
fragments1 as they strike against one   
another in  the air during their rise   
and fall1 is one of the most noteworthy 
accompaniments of volcanic eruptions4   
,it has been noticed that in many  cases
 there is a constant diminution in the  
size of the fragments  ejected during a 
volcanic outburst1 this being doubtless 
due to the  friction of the masses as   
they are ejected and re-ejected from the
  vent4 ,thus it is related by ,mr4     
,poulett ,scrope1 who watched the       
,vesuvian eruption of #ahbb1 which      
lasted for nearly a month1 that  during 

the earlier stages of the outburst      
fragments of enormous size  were thrown 
out of the crater1 but by constant      
re-ejection these were  gradually       
reduced in size1 till at last only the  
most impalpable dust  issued from the   
vent4 ,this dust filled the atmosphere1 
producing in  the city of ,naples 'a    
darkness that might be felt1' and so    
excessively  finely divided was it1 that
 it penetrated into all drawers1 boxes1 
and  the most closely fastened          
receptacles1 filling them completely4   
,mr4  ,whymper relates that1 while      
standing on the summit of ,chimborazo1  
he  witnessed an eruption of ,cotopaxi1 
which is distant more than fifty  miles 
from the former mountain4 ,the fine     
volcanic dust fell in great  quantities 
around him1 and he estimated that no    
less than two millions  of tons must    
have been ejected during this slight    
outburst4 ,professor  ,bonney has       
examined this volcanic dust from        
,cotopaxi1 and calculates  that it would

 take from #d1jjj to #be1jjj particles  
to make up a grain in  weight4          
,various names have been given by       
geologists to the fragments ejected     
from volcanic vents1 which1 as we have  
seen1 differ greatly in their           
dimensions and other characters4        
,sometimes masses of more or less  fluid
 lava are flung bodily to a great height
 in the atmosphere4  ,during their rise 
and fall these masses are caused to     
rotate1 and in  consequence assume a    
globular or spheroidal form4 ,the water 
imprisoned  in these masses1 during     
their passage through the atmosphere1   
tends to  expand into steam1 and they   
become more or less completely distended
  with bubbles4 ,such masses1 which     
sometimes assume very regular and       
striking forms1 are known as 'volcanic  
bombs4' ,many volcanic bombs have  a    
solid nucleus of refractory materials4  
,the large1 rough1 angular1             
cindery-looking fragments are termed    
'scori4' ,when reduced to the           

dimensions of a marble or pea they are  
usually called by the ,italian  name of 
'lapilli4' ,the still finer materials   
are known as volcanic sand  and dust4   
,there are1 however1 two names which are
 frequently applied to these            
fragmentary materials ejected from      
volcanoes1 which are perhaps  liable to 
give rise to misconception4 ,these are  
the terms 'cinders'  and 'ashes4' ,it   
must be remembered that the scori or    
cindery-looking  masses are not1 like   
the cinders of our fires1 the product of
 the  partial combustion of a material  
containing inflammable gases1 but are1  
like the clinkers of furnaces and       
brick-kilns1 portions of partially      
vitrified and fused rock distended by   
gases4 ,so1 too1 volcanic ashes  only   
resemble the ashes of our grates in     
being very finely divided2  they are    
not1 like the latter1 the incombustible 
residue of a mass  which has been burnt4
    ,sidenote3 ,,volcanic ,,bombs ,,and 
,,pele',s ,,hair4    ,the glassy lavas1 

when distended by escaping gases1 give  
rise to the  formation of pumice1 the   
white colour of which1 as in the case of
 the  foam of a wave1 is due to the     
reflection of a portion of the light in 
its frequent passage from one medium to 
another--in this case from  air to      
glass1 and from glass to air4 ,the      
volcanic bombs formed from  glassy lavas
 are often of especially beautiful and  
regular forms4  ,sometimes the passage  
of steam through a mass of molten glass 
produces  large quantities of a material
 resembling spun glass4 ,small particles
  or shots of the glass are carried into
 the air and leave behind them  thin1   
glassy filaments like a tail4 ,at the   
volcano of ,kilauea in ,hawaii  this    
filamentous volcanic glass is abundantly
 produced1 and is known  as ',pele's    
,hair'--,pele being the name of the     
goddess of the mountain4  ,birds' nests 
are sometimes found composed of this    
beautiful material4  ,in recent years an
 artificial substance similar to this   

,pele's hair  has been extensively      
manufactured by passing jets of steam   
through the  molten slag of             
iron-furnaces2 it resembles cotton-wool1
 but is made up  of fine threads of     
glass1 and is employed for the packing  
of boilers  and other purposes4    ,the 
very finely-divided volcanic dust is    
often borne to enormous  distances from 
the volcano out of which it has been    
ejected4 ,the force  of the             
steam-current carrying the fragments    
into the atmosphere is  often so great  
that they rise to the height of several 
miles above  the mountain4 ,here they   
may actually pass into the upper        
currents of  the atmosphere and be borne
 away to the distance of many hundreds  
or thousands of miles4 ,hence it is not 
an unusual circumstance for  vessels at 
sea to encounter at great distances from
 land falling  showers of this finely   
divided1 volcanic dust4 ,we sometimes   
meet with  this far-travelled1 volcanic 
dust under very unexpected              

circumstances4  ,thus1 in the spring of 
#ahge ,i had occasion to visit ,prof4   
,vom ,rath of  ,bonn1 who showed me a   
quantity of fine volcanic dust which had
 during  the past winter fallen in      
considerable quantities in certain parts
  of ,norway4 ,this dust1 upon          
microscopic examination1 proved to be so
  similar to what was known to be       
frequently ejected from the ,icelandic  
volcanoes that a strong presumption was 
raised that volcanic outbursts  had been
 going on in that island4 ,on returning 
to ,england ,i found that  the first    
steamer of the season had just reached  
,leith from ,iceland1  bringing the     
intelligence that very violent eruptions
 had taken place  during the preceding  
months4    ,sidenote3 ,,dispersion ,,of 
,,pumice ,,and ,,volcanic ,,dust4       
,this finely-divided volcanic dust is   
thus carried by the winds and  spread   
over every part of the ocean4 ,everyone 
is familiar with the  fact that pumice  
floats upon water2 this it does1 not    

because it is a  material specifically  
lighter than water1 but because cavities
 filled  with air make up a great part  
of its bulk4 ,if we pulverise pumice1 we
  find the powder sinks readily in      
water1 but the rock in its natural      
condition floats for the same reason    
that an iron ship does--because  of the 
air-chambers which it encloses4 ,when   
this pumice is ejected from  a volcano  
and falls into a river or the ocean1 it 
floats for a long  time1 till           
decomposition causes the breaking down  
of the thin glassy  partitions between  
the air chambers1 and causes the        
admission of water  into the latter1 by 
which means the whole mass gets         
water-logged4 ,near  the ,liparis and   
other volcanic islands the sea is       
sometimes covered  with fragments of    
pumice to such an extent that it is     
difficult for a  boat to make progress  
through it1 and the same substance is   
frequently  found floating in the open  
ocean and is cast up on every shore4    

,during the year #ahgh masses of        
floating pumice were reported as        
existing in the vicinity of the ,solomon
 ,isles1 and covering the surface  of   
the sea to such extent that it took     
ships three days to force their  way    
through them4 ,sometimes these masses of
 pumice accumulate in such  quantities  
along coasts that it is difficult to    
determine the position  of the shore    
within a mile or two1 as we may land and
 walk about on  the great floating raft 
of pumice4 ,now1 recent deep-sea        
soundings1  carried on in the           
',challenger' and other vessels1 have   
shown that the  bottom of the deepest   
portion of the ocean1 far away from the 
land1 is  covered with these volcanic   
materials which have been carried       
through  the air or floated on the      
surface of the ocean4 ,to these deeper  
parts  of the ocean no sediments carried
 down by the rivers are borne1 and the  
remains of calcareous organisms are1 in 
these abysses1 soon dissolved2  under   

such conditions1 therefore1 almost the  
only material accumulating  on the sea  
bottom is the ubiquitous wind- and      
wave-borne volcanic  products4 ,these   
particles of volcanic dust and fragments
 of pumice by  their disintegration give
 rise to a clayey material1 and the     
oxidation  of the magnetite1 which all  
lavas contain1 communicates to the mass 
a  reddish tint4 ,this appears to be the
 true origin of those masses of         
'red-clay' which1 according to recent   
researches1 are found to cover  all the 
deeper parts of the ocean1 but which    
probably attain to no  great thickness4 
,but while some portion of the materials
 ejected from volcanoes may  thus be    
carried by winds and waves1 so as to be 
dispersed over every  part of the land  
and the ocean-bed1 another1 and in most 
cases by far  the largest1 portion of   
these ejections falls around the        
volcanic vent  itself4 ,it is by the    
constant accumulation of these ejected  
materials  that such great mountain     

masses as ,etna1 ,teneriffe1 ,fusiyama1 
and  ,chimborazo have been gradually    
built up around centres of volcanic     
action4    ,there are cases in which the
 formation of volcanic mountains on a   
small  scale has actually been observed 
by trustworthy witnesses4 ,there are    
other cases in which volcanic mountains 
of larger size can be shown  to have    
increased in height and bulk by the fall
 upon their sides and  summits of       
fragmentary materials ejected from the  
volcanic vent4 ,in all  cases the       
examination of these mountain-masses    
leads to the conclusion  that they are  
entirely built up of just such materials
 as we constantly  see thrown out of    
volcanoes during eruption4    ,sidenote3
 ,,formation ,,of ,,volcanic            
,,mountains4    ,thus we are led to the 
conclusion that all volcanic mountains  
are  nothing but heaps of materials     
ejected from fissures in the earth's    
crust1 the smaller ones having been     
formed during a single volcanic         

outburst1 the larger ones being the     
result of repeated eruptions from  the  
same orifice which may1 in some cases1  
have continued in action for  tens or   
hundreds of thousands of years4    ,no  
observer has done such useful work in   
connection with the study of  the mode  
of formation of volcanic mountains as   
our countryman1 ,sir  ,william          
,hamilton1 who was ambassador at ,naples
 from #agfd to #ahjj1 and  made the best
 possible use of his opportunities for  
examining the  numerous volcanoes in    
,southern ,italy4    ,a little to the   
west of the town of ,puzzuoli on the    
,bay of ,naples there  stands a conical 
hill rising to the height of #ddj feet  
above the level  of the ,mediterranean1 
and covering an area more than half a   
mile in  diameter4 ,now we have the most
 conclusive evidence that in ancient    
times no such hill existed on this site1
 which was partly occupied by  the      
,lucrine ,lake1 and the fact is         
recognised in the name which the hill   

bears1 that of ,monte ,nuovo1 or the    
',new ,mountain4' ,see fig4 #aj4    ,sir
 ,william ,hamilton rendered admirable  
service to science by  collecting all   
the contemporary records relating to    
this interesting  case1 and he was able 
to prove1 by the testimony of several   
intelligent and trustworthy witnesses1  
that during the week following  the     
#bith of ,september1 #aech1 this hill   
had gradually been formed of  materials 
ejected from a volcanic vent which had  
opened upon this site4    ,illustration3
 ,fig4 #aj4 ,monte ,nuovo 7#ddj ft4     
high7 on the shores of the  ,bay of     
,naples4    ,sidenote3 ,,history ,,of   
,,the ,,formation ,,of ,,monte ,,nuovo4 
,the records collected by ,hamilton with
 others which have been  discovered     
since his death prove most conclusively 
the following  facts4 ,during more than 
two years1 the country round was        
affected  by earthquakes1 which         
gradually increased in intensity and    
attained  their climax in the month of  

,september #aech2 on the #bgth and #bhth
 of  that month these earthquake shocks 
are said to have been felt almost       
continuously day and night4 ,about #h   
o'clock on the morning of the #bith1  a 
depression of the ground was noticed on 
the site of the future hill1  and from  
this depression1 water1 which was at    
first cold and afterwards  tepid1 began 
to issue4 ,four hours afterwards the    
ground was seen to  swell up and open1  
forming a gaping fissure1 within which  
incandescent  matter was visible4 ,from 
this fissure numerous masses of stone1  
some of  them 'as large as an ox1' with 
vast quantities of pumice and mud1 were 
thrown3 up to a great height1 and these 
falling upon the sides of the  vent     
formed a great mound4 ,this violent     
ejection of materials continued  for two
 days and nights1 and on the third day a
 very considerable hill  was seen to    
have been built up by the falling       
fragments1 and this hill  was climbed by
 some of the eye-witnesses of the       

eruption4 ,the next day  the ejections  
were resumed1 and many persons who had  
ventured on the  hill were injured1 and 
several killed by the falling stones4   
,the later  ejections were however of   
less violence than the earlier ones1 and
 seem  to have died out on the seventh  
or eighth day after the beginning of    
the outburst4 ,the great mass of this   
considerable hill would appear1         
according to the accounts which have    
been preserved1 to have been built  up  
by the materials which were ejected     
during two days and nights4    ,monte   
,nuovo is a hill of truncated conical   
form1 which rises to the  height of #ddj
 feet above the waters of the           
,mediterranean1 and is now  covered with
 thickets of stone-pine4 ,the hill is   
entirely made up  of volcanic scori1    
lapilli1 and dust1 and the sloping sides
 have  evidently been produced by these 
fragmentary materials sliding over one  
another till they attained the angle of 
rest2 just as happens with the  earth   

and stones tipped from railway-waggons  
during the construction of  an          
embankment4 ,in the centre of this      
conical hill is a vast circular         
depression1 with steeply sloping sides1 
which is of such depth that its  bottom 
is but little above the sea-level4 ,this
 cup-shaped depression is  the 'crater' 
of the volcano1 and it has evidently    
been formed by the  explosive action    
which has thrown out the materials      
immediately above  the vent1 and caused 
them to be accumulated around it4       
,illustration3 ,fig4 #aa4--,map of the  
district around ,naples1 showing  ,monte
 ,nuovo and the surrounding volcanoes of
 older date4    ,the district lying to  
the west of ,naples1 in which the ,monte
 ,nuovo is  situated1 contains a great  
number of hills1 all of which present a 
most  striking similarity to that       
volcano4 ,all these hills are truncated 
cones1 with larger or smaller circular  
depressions at their summits1  and they 
axe entirely composed of volcanic scori1

 lapilli1 and dust4  ,some of these     
hills are of considerably larger        
dimensions than the  ,monte ,nuovo1     
while others are of smaller size1 as    
shown in the annexed  map1 fig4 #aa4 ,no
 stranger visiting the district1 without
 previous  information upon the subject1
 would ever suspect the fact that1 while
  all the other hills of the district   
have existed from time immemorial1  and 
are constantly mentioned in the works of
 ,greek and ,roman writers1  this       
particular hill of ,monte ,nuovo came   
into existence less than #cej  years    
ago4    ,sidenote3 ,,older ,,volcanoes  
,,of ,,the ,,campi ,,phlegr,i4    ,the  
evidently fused condition of the        
materials of which these hills are      
built up is a dear sign of the volcanic 
action which has taken place  in it2 and
 this feet was so fully recognised by   
the ancients that they  called the      
district the ,campi ,phlegri1 or 'the   
,burning ,fields1' and  regarded one of 
the circular depressions in it as the   

entrance to ,hades4    ,it is impossible
 for anyone to examine this district    
without being  convinced that all the   
numerous cones and craters which cover  
it  have been formed by the same agency 
as that by which ,monte ,nuovo was      
produced4 ,we have shown that there is  
the most satisfactory historical        
evidence as to what that agency was4    
,now volcanic cones with craters in     
their centres occur in great numbers  in
 many parts of the earth's surface4 ,in 
some districts1 like the  ,auvergne1 the
 ,catacecaumene in ,asia ,minor1 and    
certain parts of ,new  ,zealand1 these  
volcanic cones occur by hundreds and    
thousands4 ,in some  instances1 these   
volcanic cones have been formed in      
historic times1  but in the great       
majority of cases we can only infer     
their mode of  origin from their        
similarity to others of which the       
formation has been  witnessed4    ,most 
of the smaller volcanic hills1 with     
their craters1 have been  thrown up     

during a single eruption from a volcanic
 fissure2 but1 as  ,hamilton            
conclusively proved1 the grandest       
volcanic mountains must  have been      
produced by frequent repetitions of     
similar operations upon  the same site4 
,for not only are these great volcanic  
piles found to be  entirely composed of 
materials which have evidently been     
ejected from  volcanic vents1 but1 when 
carefully watched1 such mountains are   
found  undergoing continual changes in  
form1 by the addition of materials      
thrown out from the vent1 and falling   
upon their sides4    ,this fact will be 
well illustrated by a comparison of the 
series of  drawings of the summit of    
,vesuvius which were made by ,sir       
,william  ,hamilton in #agfg1 and which 
we have copied in fig4 #ab4 ,during the 
earlier months of that year the summit  
of the mountain was seen to be  of      
truncated form1 a great crater having   
been originated by the violent          
outbursts of the preceding year4 ,this  

condition of the mountain-top  is       
represented in the first figure of the  
series4 ,the drawing made by  ,hamilton1
 on ,july #h1 shows that not only was   
the outer rim of the great  crater being
 modified in form by the fall of        
materials upon it1 but  that in the     
centre of the crater a small cone was   
being gradually built  up by the quiet  
ejections which were taking place4      
,illustration3 ,fig4 #ab4--,outlines of 
the ,summit of ,vesuvius during the     
,eruption of #agfg4    ,sidenote3       
,,changes ,,in ,,form ,,of ,,vesuvius4  
,if we compare the drawings made at     
successive dates1 we shall find that    
the constant showers of falling         
materials were not only raising the     
edge of the great crater but were at the
 same time increasing the size  of the  
small cone inside the crater4 ,by the   
end of ,october the small  cone had     
grown to such an extent that its sides  
were confluent with  those of the       
principal cone1 which had thus entirely 

lost its truncated  form and been raised
 to a much greater height4 ,the         
comparison of these  drawings will be   
facilitated by the dotted lines1 which  
represent  the outline of the top of the
 mountain at the preceding observation2 
so that the space between the dotted and
 the continuous line in each  drawing   
shows the extent to which the bulk of   
the cone had increased in  the interval 
between two observations4    ,but1      
although the general tendency of the    
action going on at volcanic  mountains  
is to increase their height and bulk by 
the materials falling  upon their       
summits and aides1 it must be remembered
 that this action  does not take place  
by any means continuously and regularly4
 ,not only  are there periods of rest in
 the activity of the volcano1 during    
which  the rain and winds may accomplish
 a great deal in the way of crumbling   
down the loose materials of which       
volcanic mountains are largely built    
up1 but sudden and violent eruptions may

 in a very short time undo the  slow    
work of years by blowing away the whole 
summit of the mountain at  once4 ,thus1 
before the great eruption of #ahbb1 the 
cone of ,vesuvius1 by  the almost       
constant ejection of ashes during       
several years1 had been  raised to the  
height of more than #d1jjj feet above   
the level of the  sea2 but by the       
terrible outburst which then took place 
the cone was  reduced in height by #djj 
feet1 and a vast crater1 which had a    
diameter  of nearly a mile1 and a depth 
of nearly #a1jjj feet 7see fig4 #ac71   
was  formed at the top of the mountain4 
,the enormous quantity of material  thus
 removed was either distributed over the
 flanks of the mountain1  or1 when      
reduced to a finely comminuted          
condition1 was carried by the  wind to  
the distance of many miles1 darkening   
the air1 and coating the  surface of the
 ground with a thick covering of dust4  
,illustration3 ,fig4 #ac4--;,crater of  
,vesuvius formed during the eruption  in

 #ahbb4 7,it was nearly #a mile in      
diameter and #a1jjj ft4 deep47          
,sidenote3 ,,early ,,history ,,of       
,,vesuvius4    ,the volcano of          
,vesuvius1 although of somewhat         
insignificant dimensions  when compared 
with the grander volcanic mountains of  
the globe1  possesses great interest for
 the student of ,vulcanology1 inasmuch  
as  being situated in the midst of a    
thickly populated district and in  close
 proximity to the city of ,naples1 it   
has attracted much attention  during    
past times1 and there is no other       
volcano concerning which we  have so    
complete a series of historical records4
 ,the present cone of  ,vesuvius1 which 
rises within the great encircling       
crater-ring of ,somma1  has a height of 
about #a1jjj feet4 ,but there is        
undoubted evidence that  this cone1 to  
the top of which a railway has recently 
been constructed  for the convenience of
 tourists1 has been entirely built up   
during the  last #a1hjj years1 and1 what

 is more1 that during this period it has
  been many times almost wholly         
destroyed and reconstructed4    ,nothing
 is more certain than the bet that the  
,vesuvius upon which the  ancient       
,romans and the ,greek settlers of      
,southern ,italy looked1 was a  mountain
 differing entirely in its form and     
appearance from that with  which we are 
familiar4 ,the ,vesuvius known to the   
ancients was a great  truncated cone1   
having a diameter at its base of eight  
or nine miles1  and a height of about   
#d1jjj feet4 ,the summit of this        
mountain was  formed by a circular      
depressed plain1 nearly three miles in  
diameter1  within which the gladiator   
,spartacus1 with his followers1 were    
besieged by a ,roman army4 ,there is no 
evidence that at this time the  volcanic
 character of the mountain was generally
 recognised1 and its  slopes are        
described by the ancient geographers as 
being clothed with  fertile fields and  
vineyards1 while the hollow at the top  

was a waste  overgrown with wild vines4 
,illustration3 ,fig4 #ad4--;,crater of  
,vesuvius in #agef4 7,from a drawing    
made on the spot7    ,but in the year   
#gi a terrible and unexpected eruption  
occurred1 by  which a vast1 crateral    
hollow was formed in the midst of       
,vesuvius1 and  all the southern side of
 the great rim surrounding this crater  
was  broken down4 ,under the materials  
ejected during this eruption1 the       
cities of ,pompeii1 ,herculaneum1 and   
,stabi were overwhelmed and buried4     
,numerous descriptions and drawings     
enable us to understand how in the      
midst of the vast crater formed in the  
year #gi the modern cone has  gradually 
been built up4 ,fresh eruptions are     
continually increasing the  bulk1 or    
raising the height of the ,vesuvian     
cone4    ,the accompanying drawings made
 by ,sir ,william ,hamilton enable us to
  understand the nature of the changes  
which have been continually  taking     
place at the summit of ,vesuvius4 ,the  

drawing fig4 #ad shows the  appearance  
presented by the crater in the year     
#agef4    ,illustration3 ,fig4          
#ae4--,the ,summit of ,vesuvius in      
#agfg4 7,from an  original drawing47    
,sidenote3 ,,vesuvius ,,in ,,modern     
,,times4    ,at this time we see that   
inside the crater a series of cones had 
been  built up one within the other from
 which lava issued1 filling the  bottom 
of the crater and finding its way       
through a breach in its walls1  down the
 side of the cone4 ,it is evident that  
the ejected materials  falling on the   
sides of the innermost cone would tend  
to enlarge the  latter till its sides   
became confluent with the cone          
surrounding it1  and if this action went
 on long enough1 the crater would be    
entirely  filled up and a perfect cone  
with only a small aperture at the top   
would be produced4 ,but from time to    
time1 grand and paroxysmal  outbursts   
have occurred at ,vesuvius1 which have  
truncated the cone1  and sometimes      

formed great1 cup-shaped cavities1      
reaching almost to its  base1 like that 
shown in fig4 #ac4    ,in #agfg the     
crater of ,vesuvius1 as shown in fig4   
#ae1 contained a single  small cone in a
 state of constant spasmodic outburst1  
like that of  ,stromboli4               
,illustration3 ,fig4 #af4--,summit of   
,vesuvius in #ahdh4    ,in #ahdc1 we    
find that the crater of ,vesuvius       
contained three such small  cones       
arranged in a line along its bottom as  
depicted in fig4 #af4    ,these drawings
 of the summit of ,vesuvius give a fair 
notion of the  changes which have been  
continually going on there during the   
whole of  the historical period4 ,ever  
and anon a grand outburst1 like that of 
#ahbb1 has produced a vast and deep     
crater such as is represented in  fig4  
#ac1 and then a long continuance of     
quiet and regular ejections  has built  
up within the crater small cones like   
those shown in figs4  #ad1 #ae and #af1 
till at last the great crater has been  

completely filled  up1 and the cone     
reconstructed4    ,illustration3 ,fig4  
#ag4--,outlines of ,vesuvius1 showing   
its ,form at  different periods of its  
history4    ,sidenote3 ,,changes ,,in   
,,outline ,,of ,,vesuvius4    ,in the   
series of outlines in fig4 #ag1 we have 
endeavoured to illustrate  the          
succession of changes which has taken   
place in ,vesuvius during  historical   
times4 ,in the year #gi one side of the 
crater-wall of the  vast mountain-mass  
was blown away4 ,subsequent ejections   
built up the  present cone of ,vesuvius 
within the great encircling crater-wall 
of  ,somma1 and the form of this cone   
and the crater at its summit have  been 
undergoing continual changes during the 
successive eruptions of  eighteen       
centuries4    ,what its future history  
may be we can only conjecture from      
analogy4  ,it may be that a long        
continuance of eruptions of moderate    
energy may  gradually raise the central 
cone till its sides are confluent with  

those of the original mountain2 or it   
may be that some violent paroxysm  will 
entirely destroy the modern cone1       
reducing the mountain to the  condition 
in which it was after the great outburst
 of #gi4 ,on the other  hand1 if the    
volcanic forces under ,vesuvius are     
gradually becoming  extinct 7but of this
 we have certainly no evidence at       
present71 the  mountain may gradually   
sink into a state of quiescence1        
retaining its  existing form4    ,the   
series of changes in the shape of       
,vesuvius1 which are proved by          
documentary evidence to have been going 
on during the last #b1jjj years1        
probably find their parallel in all     
active volcanoes4 ,in all of these1  as 
we shall hereafter show1 the activity of
 the vents undergoes great              
vicissitudes4 ,periods of continuous    
moderate activity alternate with  short 
and violent paroxysmal outbursts and    
intervals of complete rest1  which may  
in some cases last for hundreds or even 

thousands of years4  ,during the periods
 of continuous moderate activity1 the   
crater of the  volcano is slowly filled 
up by the growth of smaller cones within
 it2  and the height of the mountain is 
raised4 ,by the terrible paroxysmal     
outbursts the mountain is often         
completely gutted and its summit blown  
away2 but the materials thus removed    
from the top and centre of the  mass are
 for the most part spread over its      
aides1 so that its bulk  and the area of
 its base are thereby increased4 ,during
 the intervals  of rest1 the sides of   
the mountain which are so largely       
composed of  loose and pulverulent      
materials are washed downwards by rains 
and  driven about by winds4 ,thus all   
volcanoes in a state of activity are    
continually growing in size every       
ejection1 except in the case of those   
where the materials are in the finest   
state of subdivision1 adding to  their  
bulk2 the area of their bases being     
increased during paroxysmal  outbursts1 

and their height during long-continued  
moderate eruptions4    ,sidenote3       
,,deviations ,,from ,,conical ,,form4   
,we have pointed out that the conical   
form of volcanic mountains is  due to   
the slipping of the falling materials   
over one another till  they attain the  
angle at which they can rest4 ,there    
are1 however1 some  deviations from this
 regular conical form of volcanoes which
 it may be  well to refer to4    ,the   
quantity of rain which falls during     
volcanic eruptions is often  enormous1  
owing to the condensation of the great  
volumes of steam  emitted from the vent4
 ,consequently the falling lapilli and  
dust often  descend upon the mountain1  
not in a dry state but in the condition 
of a muddy paste4 ,many volcanic        
mountains have evidently been built  up 
by the flow of successive masses of such
 muddy paste over their  surfaces4 ,some
 volcanic materials when mixed with     
water have the  property of rapidly     
'setting' like concrete4 ,the ancient   

,romans and  modern ,italians1 well     
acquainted with this property of certain
 kinds of  volcanic dust and lapilli1   
have in all ages employed this          
'puzzolana1'  as it is called1 as mortar
 for building4 ,the volcanic muds have  
often  set in their natural positions1  
so as to form a rock1 which1 though     
light and porous1 is of tolerably firm  
consistency4 ,to this kind of  rock1 of 
which ,naples and many other cities are 
built1 the name of  'tuff' or 'tufa' is 
applied4 ,a similar material is known in
 ,northern  ,germany as 'trass4'    ,the
 cause of the 'setting' of puzzolana and
 tufa is that rain-water  containing a  
small proportion of carbonic acid acts  
on the lime in the  volcanic fragments1 
and these become cemented together by   
the carbonate  of lime and the free     
silica1 which are thus produced in the  
mass4    ,when a strong wind is blowing 
during a volcanic outburst1 the         
materials  may be driven to one side of 
the vent1 and accumulate there more     

rapidly than on the other4 ,thus        
lop-sided cones are formed1 such  as may
 frequently be observed in some volcanic
 districts4 ,in areas  where constant   
currents of air1 like the trade-winds1  
prevail1 all  the scoria-cones of the   
district may thus be found to be        
unequally  developed on opposite sides1 
being lowest on those from which the    
prevalent winds blow1 and highest on the
 sides towards which these  winds blow4 
,sidenote3 ,,angle ,,of ,,slope ,,in    
,,volcanic ,,cones4    ,the examination 
of any careful drawing1 or better still 
of the  photograph1 of a volcanic cone1 
will prove that the profile of such     
cones is not formed by straight lines1  
but by curves often of a  delicate and  
beautiful character4 ,the delineations  
of the sacred  volcano of ,fusiyama1    
which are so constantly found in the    
productions  of ,japanese artists1 must 
have familiarised everyone with the     
elegant  curved lines exhibited by the  
profiles of volcanoes4 ,the upper slope 

of the mountain is comparatively steep1 
often exhibiting angles of  #cj to #ce1 
but this steepness of slope gradually   
diminishes1 till it  eventually merges  
in the surrounding plains4 ,the cause of
 this elegant  form assumed by most     
volcanic mountains is probably two-fold4
 ,in the  first place we have to        
remember that the materials falling upon
 the  flanks of the mountain differ in  
size and shape1 and some will rest  on a
 steeper slope than others4 ,thus1 while
 some of the materials  remain on the   
upper part of the mountains1 others are 
rolling outwards  and downwards4 ,hence 
we find that those cones which are      
composed of  uniform materials have     
straight sides4 ,but in some cases1 we  
shall  see hereafter1 there has         
certainly been a central subsidence of  
the  mountain mass1 and it is this      
subsidence which has probably given rise
  to the curvature of its flanks4    ,we
 have hitherto considered only the      
methods by which the froth or  foam1    

which accumulates on the surface of     
fluid lava1 is dispersed4  ,but in many 
cases not only is this scum of the lava 
ejected from the  volcanic vent by the  
escaping steam1 but the fluid lava      
itself is  extruded forcibly1 and often 
in enormous quantities4    ,the lava in 
a volcanic vent is always in a highly   
heated1 usually  incandescent1          
condition4 ,seen by night1 its freshly  
exposed surface  is glowing red1        
sometimes apparently white-hot4 ,but by 
exposure to  the atmosphere the surface 
is rapidly chilled1 appearing dull red  
by  night1 and black by day4 ,many      
persons are surprised to find that a    
flowing stream of lava presents the     
appearance of a great mass of rough     
cinders1 rolling along with a rattling  
sound1 owing to the striking of  the    
clinker-like fragments against each     
other4 ,when viewed by night1  the      
gleaming1 red light between these rough1
 cindery masses betrays the  presence of
 incandescent materials below the       

chilled surface of the  lava-stream4    
,no fact in connection with lavas is    
more striking than the varying  degrees 
of liquidity presented by them in       
different cases4 ,while some            
lava-streams seem to resemble rivers1   
the material flowing rapidly  along1    
filling every channel in its course1 and
 deluging the whole  country around1    
others would be more fitly compared to  
glaciers1  creeping along at so slow a  
rate that the fact of their movement can
  only be demonstrated by the most      
careful observation4 ,even when falling 
over a precipice such lavas1 owing to   
their imperfect liquidity1 form  heavy1 
pendent masses like a 'guttering'       
candle1 as is shown by fig4  #ah1 which 
is taken from a drawing kindly furnished
 to me by ,capt4 ,s4 ,p4  ,oliver1      
,r4,a4 ,the causes of these differences 
in the rate of motion of  lava-streams  
we must proceed to consider4            
,illustration3 ,fig4 #ah4--;,cascade of 
,lava tumbling over a cliff in the      

,island of ,bourbon4    ,sidenote3      
,,temperature ,,of ,,lava-,,streams4    
,there can be no doubt that the         
temperature of lavas varies greatly in  
different cases4 ,this is shown by the  
fact that while some lavas are in  a    
state of complete fusion1 similar to    
that of the slags of furnaces1  and like
 the latter1 such lavas on cooling form 
a glassy mass1 others  consist of a     
liquid magma in which a larger or       
smaller number of  crystals are found   
floating4 ,in these latter cases the    
temperature of  the magma must be below 
the fusing-point of the minerals which  
exist  in a crystalline condition in its
 midst4 ,it has indeed been suggested   
that the whole of the crystals in lavas 
are formed during the cooling  down of a
 completely fused mass2 but no one can  
imagine that the  enclosed crystals of  
quartz1 felspar1 leucite1 olivine1 c41  
have  been so formed1 such crystals     
being sometimes more than an inch in    
diameter4 ,the microscopic examination  

of lavas usually enables us to          
discriminate between those complete     
crystals which have been formed at      
great depths and carried up to the      
surface1 and the minute crystalline     
particles and microliths which have been
 developed in the glassy mass  during   
cooling4 ,crystals of the former class1 
indeed1 exhibit abundant  evidence1 in  
their liquid cavities and other         
peculiarities1 that they  have not been 
formed by simple cooling from a state of
 fusion1 but  under the combined action 
of heat1 the presence of water and      
various  gases1 and intense pressure4   
,as we have already seen1 the different 
lavas vary greatly in their  degrees of 
fusibility4 ,the basic lavas1 containing
 a low percentage  of silica1 are much  
more fusible than the acid lavas1 which 
contain  a high percentage of silica4   
,when the basic lavas are reduced to a  
complete state of fusion their liquidity
 is sometimes very perfect1 as  is the  
case at ,kilauea in ,hawaii1 where the  

lava is thrown up into jets  and        
fountains1 falling in minute drops1 and 
being drawn out into fine  glassy       
threads4 ,on the other hand1 the less   
fusible acid lavas appear  to be usually
 only reduced to the viscous or pasty   
condition1 which  artificial glasses    
assume long before their complete       
fusion4 ,of this  fact ,i have found    
many proofs in the ,lipari ,islands1    
where such glassy1  acid lavas abound4  
,in fig4 #f 7page #dc7 a lava-stream is 
represented on  the side of the cone of 
,vulcano4    ,sidenote3 ,,imperfectly   
,,fluid ,,lavas4    ,this lava is an    
obsidian--that is to say1 it is of the  
add type and  completely glassy--but its
 liquidity must have been very          
imperfect1  seeing that the stream has  
come to a standstill before reaching the
  bottom of a steep slope of about #ce4 
,in fig4 #ai there is given a side  view
 of the same stream of obsidian1 from   
which it will be seen that  it has      
flowed slowly down a steep slope and    

heaped itself up at the  bottom1 as its 
fluidity was not complete enough to     
enable it to move on  a slighter        
incline4 ,an examination of the interior
 of such imperfectly  fluid lavas       
affords fresh proofs of the slow and    
tortuous movements  of the mass4        
,everywhere we find that the bands of   
crystallites and  sphrulites are1 by the
 movement of the mass1 folded and       
crumpled and  puckered in the most      
remarkable manner1 as is illustrated in 
figs4 #bj  and #ba4 ,similar appearances
 occur again and again among the        
vitreous  and semi-vitreous acid lavas  
of ,hungary4    ,illustration3 ,fig4    
#ai4--,lava-stream 7obsidian7 in the    
,island of  ,vulcano showing the        
imperfect liquidity of the mass4        
,illustration3 ,fig4 #bj4--;,interior of
 a ,rhyolitic ,lava-stream in the       
,island of ,lipari1 showing broad       
sigmoidal folds produced by the slow    
movements of the mass4    ,illustration3
 ,fig4 #ba4--;,interior of a ,rhyolitic 

,lava-stream in the  ,island of ,lipari1
 showing the complicated crumplings and 
puckerings  produced by the slow        
movements of the mass4    ,sidenote3    
,,rate ,,of ,,movement ,,of ,,vesuvian  
,,lavas4    ,but1 although the          
temperature of lava-streams and the     
fusibility of  their materials may in   
some cases account for their condition  
of  either perfect liquidity or         
viscidity1 it is clear that in other    
instances there must be some other cause
 for this difference4 ,thus  it has been
 found that at ,vesuvius the lavas      
erupted in modern times  have all a     
striking similarity to one another in   
chemical composition1  in the minerals  
which they contain1 and in their        
structure4 ,they are  all basic lavas1  
which when examined by the microscope   
are seen to  consist of a more or less  
glassy magma1 in the midst of which     
numerous  crystals of augite1 leucite1  
olivine1 magnetite1 and other minerals  
are scattered4 ,yet nothing can be more 

strikingly different than the  behaviour
 of the lavas poured out from ,vesuvius 
at various periods4 ,in  some cases the 
lava appears to be in such a perfectly  
liquid condition  that1 issuing from the
 crater1 it has been described as       
rushing down  the slope of the cone like
 a stream of water1 and such exceedingly
  liquid lavas have in some cases flowed
 to the distance of several  miles from 
the base of the mountain in a very short
 time4 ,but other  ,vesuvian lavas have 
been in such a viscid condition that    
their rate  of movement has been so     
extremely slow as to be almost          
imperceptible4  ,such lava-streams have 
continued in movement during many years1
 but the  progress has been so slow     
7often only a few inches in a day7 that 
it  could only be proved by means of    
careful measurements4    ,if we examine 
some of these ,vesuvian lavas which have
 exhibited such  striking differences in
 their rate of flow1 we shall find that 
they  present equally marked differences

 in the character of their surfaces4    
,the lava-current of #aheh was a        
remarkable example of a slow-flowing    
stream1 and its surface1 as will be seen
 in fig4 #bb1 which is taken  from a    
photograph1 has a very marked and       
peculiar character4 ,a  tenacious crust 
seems to have formed on the surface1 and
 by the further  motion of the mass this
 crust or scum has been wrinkled and    
folded  in a very remarkable manner4    
,sometimes this folded and twisted crust
  presents a striking resemblance to    
coils of rope4 ,precisely similar       
appearances may be observed on the      
surface of many artificial slags  when  
they flow from furnaces1 and are seen to
 be due to the same  cause1 namely1 the 
wrinkling up of the chilled             
surface-crust by the  movement of the   
liquid mass below4 ,lavas which present 
this appearance  are frequently called  
'ropy lavas'2 an admirable example of   
them is  afforded in the lava-cascade of
 the ,island of ,bourbon represented in 

fig4 #ah 7page #ic74    ,but lavas in   
which the rate of flow has been very    
rapid1 exhibit  quite a different kind  
of surface to that of the ropy lavas4   
,the  ,vesuvian lava-stream of #ahgb was
 remarkable for the rapidity of its     
flow1 and its surface presents a        
remarkable contrast to that of the      
slow-moving lava of #aheh4 ,the surface 
of the lava-current of #ahgb is  covered
 with rough cindery masses1 often of    
enormous dimensions1 and  it is         
exceedingly difficult to traverse it1 as
 the ragged projecting  fragments tear  
the boots and lacerate the skin4 ,the   
appearance  presented by this           
lava-stream is illustrated by fig4 #bc1 
which is also  taken from a photograph4 
,illustration3 ,fig4 #bb4--,vesuvian    
,lava-stream of #aheh1 exhibiting the   
peculiar ',ropy' ,surfaces of ,slowly   
,moving ,currents4    7,from a          
,photograph47    ,illustration3 ,fig4   
#bc4--,vesuvian ,lava-stream of #ahgb1  
exhibiting the  ,rough ,cindery         

,surfaces characteristic of ,rapidly    
,flowing ,currents4    7,from a         
,photograph47    ,sidenote3 ,,vesuvian  
,,lava-,,stream ,,of #ahgb4    ,now it  
is found that those lava-streams which  
move slowly and present  ropy surfaces  
give off but little steam during their  
flow1 while those  lava-streams which   
flow more rapidly and present a rough   
and cindery  appearance give off vast   
quantities of steam4 ,the extraordinary 
amount  of vapour given off from the    
lava-streams which flowed from ,vesuvius
  in #ahgb is illustrated in the        
photograph copied in fig4 #e 7facing    
page  #bd71 in which the three          
lava-currents are each seen to be       
surmounted  by enormous vapour-clouds   
rising to the height of several         
thousands  of feet above them1 and      
mingling with the column that issued    
from  the central vent4 ,by the escape  
of this enormous quantity of steam  the 
surface of the lava was thrown into     
rugged cindery projections1  and in some

 places little cones were formed upon   
it1 which threw out  small scori and    
dust4 ,the quantity of vapour was1 in   
fact1 so great1  that little parasitical
 volcanoes were formed on the surface of
 the  lava-stream4 ,some of these       
miniature volcanoes were of such small  
dimensions that they were carried away  
on boards to be employed as             
illustrations in the lecture-rooms of   
the ,university of ,naples4    ,the     
arrangement of the materials forced out 
from fissures on the  surfaces of       
lava-streams by the disengaged vapours  
and gases depends  on the degree of     
fluidity of the lava1 and the force of  
the escaping  steam-jets4 ,in very      
viscous lavas the materials may issue   
quietly1  forming great concentric      
masses like coils of rope2 such were    
described  by ,mr4 ,heaphy as occurring 
in ,new ,zealand 7see fig4 #bd74        
,illustration3 ,fig4 #bd4--;,concentric 
,folds on mass of cooled ,lava4    ,in  
other cases the lava1 if somewhat more  

liquid1 may in issuing  quietly without 
great outbursts of steam1 accumulate in 
great  bottle-shaped masses1 which have 
been compared to 'petrified  fountains4'
 ,cases of this kind have been described
 by ,professor ,dana as  occurring on   
the slopes of ,hawaii 7see fig4 #be74   
,illustration3 ,fig4 #be4--,mass of     
cooled ,lava formed over a spiracle on  
the slopes of ,hawaii4    ,sidenote3    
,,miniature ,,cones ,,on                
,,lava-,,streams4    ,when the steam    
escapes with explosive violence from a  
spiracle  7'bocca'7 on the surface of a 
lava-stream1 minute cinder cones1  like 
those described as being formed in      
#ahgb1 are the result4 ,fig4  #bf       
represents a group of miniature cones   
thrown up on the ,vesuvian  lava-stream 
of #ahee3 it is taken from a drawing by 
,schmidt4    ,illustration3 ,fig4       
#bf4--;,group of small ,cones thrown up 
on the ,vesuvian  ,lava-current of      
#ahef4    ,some of these appear like    
burst blisters or bubbles1 while others 

are built up of scoriaceous masses which
 have been ejected from the  aperture   
and have become united while in a       
semi-fluid condition4 ,other  examples  
of these spiracles or bocche on the     
surfaces of lava-currents  may be seen  
in the figs4 #bb and #bc1 which are     
copied from photographs4    ,the facts  
we have described all point to the      
conclusion that the  presence of large  
quantities of water imprisoned in a mass
 of lava  contributes greatly to its    
mobility4 ,and this conclusion is       
supported  by so many other             
considerations that it is now very      
generally accepted  by geologists4 ,the 
condition of this imprisoned water in   
lavas is one  which demands further     
investigation at the hands of           
physicists4 ,it has  been suggested1    
with some show of reason1 that the water
 may exist  in the midst of the red-hot 
lava as minute particles in the curious 
'spheroidal condition' of ,boutigny1 and
 that these flash into steam as  the    

lava flows along4    ,lava1 when        
extruded from a volcanic crater in a    
more or less completely  fluid state1   
flows down the side of the cone1 and    
then finds its way  along any channel or
 valley that may lie in its course1     
obeying in its  movements all the laws  
of fluid bodies4 ,the lava-currents thus
 formed  are sometimes of enormous      
dimensions1 and may flood the whole     
country  for many miles around the vent4
    ,lava-streams have been described1  
which have flowed for a distance of     
from fifty to a hundred miles from their
 source1 and which have had  a breadth  
varying from ten to twenty miles4 ,some 
lava-streams have a  thickness of #ejj  
feet1 or even more4 ,these measures will
 give some  idea of the enormous        
quantities of material brought from the 
earth's  interior by volcanic action and
 distributed over its surface4 ,the mass
  of lava which flowed out during an    
eruption off ,reykjanes in ,iceland1  in
 the year #aghc1 has been calculated to 

be equal in bulk to ,mont ,blanc4       
,there are many parts of the earth's    
surface1 such as the ,western ,isles  of
 ,scotland and the ,north-east of       
,ireland1 the ,deccan of ,india1 and    
large tracts in the ,rocky ,mountains1  
where successive lava-sheets have  been 
piled upon one another to the height of 
several thousands of feet1  and cover   
areas of many hundreds or even thousands
 of square miles4    ,sidenote3         
,,features ,,of ,,lava-,,streams4       
,the more fusible basic lavas are as a  
general rule more liquid in  character  
than any others1 and it is these very   
liquid lavas that are  usually found    
forming plateaux built up of successive 
lava-streams4 ,the  less liquid lavas1  
like those of ,hungary and ,bohemia1 are
 not usually  found flowing to such     
distances from the vent1 but form       
dome-shaped  mountain-masses4           
,lava-streams usually exhibit in their  
upper and under surfaces a  scoriaceous 
texture due to the escape of steam from 

the upper surface1  portions of the     
cindery masses so formed falling off    
from the end of  the stream1 and being  
rolled over by the stream so as to form 
its  base4 ,the thickness of this       
scoriaceous upper and lower part of a   
lava-stream varies according to the     
quantity of steam imprisoned in  it2 but
 all thick lava-streams have a compact  
central portion which  is composed of   
hard1 solid rock4 ,very good examples of
 the internal  structure of lava-streams
 may sometimes be examined in the       
sea-cliffs  of volcanic islands4 ,in    
fig4 #bg we have given a copy of a      
drawing made  while sailing round the   
shores of ,vulcano4 ,the scoriaceous    
portions of  lava-streams are sometimes 
employed1 as at ,volvic in the          
,auvergne1 as  a building material1 or  
as at ,neidermendig in the ,eifel and in
 ,hungary  for mill-stones2 the compact 
portions are employed for building and  
paving1 and for road metal4 ,the rock of
 some of the modern lava-streams  of    

,vesuvius is largely quarried for paving
 the streets of ,naples4    ,this solid 
portion of the lava-streams in slowly   
cooling down from its  highly-heated    
condition undergoes contraction1 and in 
consequence is  rent asunder by a number
 of cracks4 ,sometimes these cracks     
assume a  wonderfully regular           
arrangement1 and the rock may be broken 
up into  very symmetrical masses4       
,illustration3 ,fig4 #bg4--,natural     
section of a ,lava-stream in the ,island
  of ,vulcano1 showing the compact      
central portion and the scoriaceous     
upper and under surfaces4    ,sidenote3 
,,columnar ,,structure ,,of ,,lavas4    
,if we imagine a great sheet of heated  
material1 like a lava-stream1  slowly   
cooling down1 it is evident that the    
contraction which must  take place in it
 will tend to produce fissures breaking 
up the mass  into prisms4 ,a little     
consideration will convince us what the 
form of  these prisms must be4 ,there   
are only three regular figures into     

which  a surface can be divided1 namely1
 equilateral triangles1 squares1 and    
regular hexagons2 the first being       
produced by the intersection of  sets of
 six lines radiating at angles of #fj   
from certain centres2  the second by the
 intersection of sets of four lines     
radiating from  centres at angles of    
#ij2 and the third from sets of three   
lines  radiating from centres at an     
angle of #abj4 ,it is evident that a    
less  amount of contractile force will  
be required to produce the sets of      
three cracks rather than those of four  
or six cracks2 or1 in other  words1 the 
contractile force in a mass will be     
competent to produce the  cracks which  
give rise to hexagons rather than those 
which form squares  or triangles4 ,this 
is no doubt the reason why the prisms   
formed by the  cooling of lava1 as well 
as those produced during the drying of  
starch  or clay1 are hexagonal in form4 
,the hexagonal prisms or columns formed 
by contraction during the  consolidation

 of lavas vary greatly in size1         
according to the rate of  cooling1 the  
nature of the materials1 and the        
conditions affecting the  mass4         
,sometimes such columns may be found    
having a diameter of eight  or ten feet 
and a length of five hundred feet1 as in
 the ,shiant ,isles  lying to the north 
of the ,island of ,skye2 in other cases1
 as in certain  volcanic glasses1 minute
 columns1 an inch or two in length and  
scarcely  thicker than a needle1 are    
formed2 and examples of almost every    
intermediate grade between these two    
extremes may sometimes be found4  ,the  
largest columns are those which are     
formed in very slowly cooling  masses4  
,the columnar structure is exhibited by 
all kinds of lava1 and indeed  in other 
rock-masses which have been heated by   
contact with igneous  masses and        
gradually cooled4 ,the rocks which      
display the structure in  greatest      
perfection1 however1 are the basalts4   
,mr4 ,scrope first called attention to  

the fact that the upper and lower       
portions of lava-streams sometimes cool 
in very different ways1 and  hence      
produce columns of dissimilar character4
 ,the lower portion of the  mass parts  
with its heat very slowly1 by conduction
 to the underlying  rocks1 while the    
upper portions radiate heat more        
irregularly into  the surrounding       
atmosphere4 ,hence we often find the    
lower portions of  thick lava-streams to
 be formed of stout1 vertical columns of
 great  regularity2 while the upper part
 is made up of smaller and less regular 
columns1 as shown in fig4 #bh4          
,illustration3 ,fig4 #bh4--,section of a
 ,lava-stream exposed on the side  of   
the river ,ardche1 in the south-west of 
,france4    ,the remarkable grotto known
 as ,fingal's ,cave in the ,island of   
,staffa  has been formed in the midst of
 a lava-stream such as we have been     
describing2 the thick vertical columns1 
which rise from beneath the  level of   
the sea1 are divided by joints and have 

been broken away by  the action of the  
sea2 in this way a great cavern has been
 produced1  the sides of which are      
formed by vertical columns1 while the   
roof is  made up of smaller and         
interlacing ones4 ,the whole structure  
bears some  resemblance to a ,gothic    
cathedral2 the sea finding access to its
 floor  of broken columns1 and          
permitting the entrance of a boat during
 fine  weather4 ,similar1 though perhaps
 less striking1 structures are found in 
many other parts of the globe wherever  
basaltic and other lava-streams  exhibit
 the remarkable columnar structure as   
the result of their slow  cooling4      
,portions of basaltic columns are often 
employed for posts  by the road-sides1  
as in ,central ,germany and ,bohemia1 or
 for paving  stones1 as in ,pompeii and 
at the ,monte ,albano near ,rome4       
,illustration3 ,fig4 #bi4--,portion of a
 ,basaltic ,column from the ,giant's    
,causeway1 exhibiting both the          
ball-and-socket and the                 

tenon-and-mortise  structures4          
,sidenote3 ,,other ,,joint-,,structures 
,,in ,,lavas4    ,occasionally basaltic 
lava-streams exhibit other curious      
structures in  addition to the columnar4
 ,thus some basaltic columns are found  
divided  into regular joints by         
equidistant1 curved surfaces1 the joints
 thus  fitting into one another by a    
kind of ball-and-socket arrangement4    
,sometimes we find processes projecting 
from the angles of the curved           
joint-surfaces1 which cause the blocks  
to fit together as with a tenon  and    
mortise4 ,this kind of structure is     
admirably displayed at the  ,giant's    
,causeway1 ,co4 ,antrim1 in the ,north  
of ,ireland4 ,a portion of a  basaltic  
column from this locality is represented
 in fig4 #bi4    ,illustration3 ,fig4   
#cj4--,vein of green ,pitchstone1 at    
,chiaja di ,luna  in the ,island of     
,ponza1 breaking up into regular        
columns1 and into  spherical masses with
 a concentric series of joints4         

,while the ordinary columnar structures 
are very common in basalts1  the        
ball-and-socket and tenon-and-mortise   
structures are exceedingly  rare4 ,the  
question of the mode of origin of these 
remarkable structures  has given rise to
 much discussion1 and the opinions of   
geologists and  physicists are by no    
means unanimous upon the subject4       
,sometimes we find masses of lava       
traversed by curved joints1 and         
occasionally we find curious            
combinations of curved and plane joints1
  giving rise to appearances scarcely   
less remarkable than those  presented by
 the columns of the ,giant's ,causeway4 
,some of the more  striking examples of 
this kind have been described and       
explained by  ,professor ,bonney4       
,illustration3 ,fig4                    
#ca4--;,illustration of the ',perlitic  
structure' in  glassy ,rocks4      a4   
,perlltic structure1 as seen in a lava  
from ,hungary4    b4 ,the same          
structure1 artificially produced in     

,canada ,balsam         during cooling4 
,sidenote3 ,,perlitic-,,structure ,,in  
,,lavas4    ,in the ,ponza ,islands     
there occurs a remarkable example of a  
columnar  pitchstone1 which is also     
traversed by a member of curved         
concentric  joints1 causing the rock to 
break up into pieces like the coats of  
an  onion4 ,this remarkable rock-mass is
 represented in fig4 #cj4    ,a very    
similar structure is often seen in      
certain glassy lavas1 when  they are    
examined in thin sections under the     
microscope4 ,such glassy  lavas exhibit 
the peculiar lustre of mother-of-pearly 
doubtless in  consequence of the        
interference of light along the cracks4 
,lavas  exhibiting this character are   
known to geologists as 'perlites4' ,the 
perlitic structure has been produced    
artificially by ,mr4 ,grenville ,cole   
in ,canada ,balsam1 and by ,,mm4 ,fonqu 
and ,michel ,lvy1 in chemically         
deposited silica4 ,see fig4 #ca4    ,a  
thick lava-stream must take an enormous 

period to cool down--probably  many     
hundreds or even thousands of years4 ,it
 is possible to walk over  lava-streams 
in which at a few inches below the      
surface the rock is  still red-hot1 so  
that a piece of stick is lighted if     
thrust into a  crack4 ,lava is a very   
bad conductor of heat1 and loose scori  
and  dust are still worse conductors4   
,during the eruption of ,vesuvius in    
#ahgb1 masses of snow which were covered
 with a thick layer of scori1  and      
afterwards by a stream of lava1 were    
found three years afterwards            
consolidated into ice1 but not melted4  
,the city of ,catania is  constantly    
supplied with ice from masses of snow   
which have been buried  under the       
ejections of ,etna4    ,during the      
cooling down of lavas1 the escape of    
steam and various  gases gives rise to  
the deposition of many beautiful        
crystalline  substances in the cavities 
and on the surfaces of the lava4        
,deposits  of sulphur1 specular-iron1   

tridymite1 and many other substances are
  often thus produced1 and the colour   
and appearance of the rock-masses  are  
sometimes completely disguised by these 
surface incrustations1 or  by the       
decomposition of the materials of the   
lava by the action of the  add gases1   
and vapours upon it4    ,sidenote3      
,,sinking ,,of ,,surfaces ,,of          
,,lava-,,streams4    ,very frequently   
the surface of a lava-stream becomes    
solid1 while the  deeper portions retain
 their fluid condition2 under such      
circumstances  the central portions may 
flow away1 leaving a great hollow       
chamber or  cavern4 ,in consequence of  
this action1 we not unfrequently find   
the  upper surface of a lava-current    
exhibiting a depression1 due to the     
falling in of the solidified upper      
portions when the liquid lava has       
flowed away and left it unsupported1 as 
in fig4 #cb4    ,illustration3 ,fig4    
#cb4--,transverse section of a ,lava    
stream4 7,the  dotted line indicates the

 original surface47          ,,chapter  
,v    ,,the ,,internal ,,structure ,,of 
,,volcanic ,,mountains4      ,near the  
high-road which passes between the towns
 of ,eger and  ,franzenbad in ,bohemia1 
there rises a small hill known as the   
,kammerbhl  7see fig4 #cc71 which has   
attracted to itself an amount of        
interest  and attention quite out of    
proportion to its magnitude or          
importance4  ,during the latter part of 
the last century and the earlier years  
of  the present one1 the fiercest       
controversies were waged between the    
partisans of rival schools of cosmogony 
over this insignificant hill2  some     
maintaining that it originated in the   
combustion of a bed of coal1  others    
that its materials were entirely formed 
by some kind of 'aqueous                
precipitation1' and others again that   
the hill was the relic of a small       
volcanic cone4    ,among those who took 
a very active part in this controversy  
was  the poet ,goethe1 who stoutly      

maintained the volcanic origin of the   
,kammerbhl1 styling it 'a pocket edition
 of a volcano4' ,to ,goethe  belongs the
 merit of having suggested a ,very      
simple method by which the              
controversies concerning this hill might
 be set at rest3 he proposed  that a    
series of excavations should be         
undertaken around the hill1 and  a      
tunnel driven right under its centre4   
,illustration3 ,fig4 #cc4--,the         
,kammerbhl of ,kammerberg1 ,bohemia4    
7,as seen from the south-west7          
,sidenote3 ,,the ,,kammerb,,hl4    ,the 
poet's friend1 ,count ,caspar von       
,sternberg1 determined to put this      
project into execution4 ,this series of 
excavations1 which was completed  in    
#ahcg1 has for ever set at rest all     
doubts as to the volcanic origin  of the
 ,kammerbhl4 ,a plug of basalt was found
 filling the centre of  the mass1 and   
connected with a small lava-stream      
flowing down the side  of the hill2     
while the bulk of the hill was shown to 

be composed of  volcanic scori and      
lapilli4 ,the section fig4 #cd will     
illustrate the  structure of the hill as
 revealed by these interesting          
excavations4    ,illustration3 ,fig4    
#cd4--,section of the ,kammerbhl1 in    
,bohemia4    a a4 ,metamorphic rocks4 b4
 ,basaltic scori4 c4 ,solid plug  of    
basalt rising through the centre of the 
volcanic pile1 d d4  ,lava-stream       
composed of the same rock4 e e4         
,alluvial matter  surrounding the old   
volcano4    7,the dotted lines indicate 
the probable former outline of the      
volcano47    ,sidenote3 ,,volcanoes     
,,dissected ,,by ,,denudation4    ,it   
can of course very seldom happen that   
actual mining operations1 like  those   
undertaken in the case of the           
,kammerbhl1 will be resorted to  in     
order to determine the structure of     
volcanic mountains4 ,geologists  have   
usually to avail themselves of less     
direct1 but by no means less  certain1  
methods than that of making artificial  

excavations in order  to investigate the
 earth's crust4 ,fortunately it happens 
that what we  cannot accomplish         
ourselves1 nature does for us4 ,the     
action which we  call 'denudation'      
serves as a scalpel to dissect volcanic 
mountains  for us1 and to expose their  
inner recesses to our view4 ,many       
portions  of the earth's surface are    
complete museums crowded with volcanic  
'subjects1' exhibiting every stage of   
the process of dissection4 ,in  some1   
rains and winds have stripped off the   
loose covering of cinders  and dust1 and
 exposed the harder and more solid      
parts--the skeleton of  the mountain4   
,in others1 the work of destruction has 
proceeded still  further1 and slowly    
wearing rivers or the waves of the sea  
may have cut  perfect1 vertical sections
 of the mountain-mass4 ,sometimes the   
removal  of the materials of the        
volcanic mountain has gone on to such an
 extent  that its base and ground-plan  
are fully exposed4 ,it only requires the

  necessary skill in piecing together   
our observations on these dissected     
volcanoes1 in order to arrive at just   
views concerning the 'comparative       
anatomy' of volcanoes4 ,as the knowledge
 of the structure of animals  remained  
in the most rudimentary condition until 
the practice of  dissection was         
commenced1 so our knowledge of volcanoes
 was likewise  exceedingly imperfect    
till geologists availed themselves of   
the  opportunities afforded to them of  
studying naturally dissected volcanic   
mountains4    ,in some cases we may find
 that the sea has encroached on the base
  of a volcanic hill1 till one half of  
it has been washed away1 and  the       
structure of the mass to its very centre
 is exposed to our view4  ,thus in fig4 
#f 7page #dc71 it will be seen that     
there lies in front of  ,vulcano a      
peninsula called ,vulcanello1 consisting
 of three volcanic  cones1 united at    
their base1 with the lava-streams which 
have flowed  from them4 ,one half of the

 cone on the left-hand side of the      
picture  has been completely washed away
 by the sea1 and a perfect section  of  
the internal structure of the cone is   
exposed4 ,the appearances  presented in 
this section are shown in the sketch1   
fig4 #ce4 ,some  portions of the face of
 this section are concealed by the heaps
 of  fragments which have fallen from   
it1 but enough is visible to convince   
us that three kinds of structures go to 
make up the cone4 ,in the first  place1 
we have the loose scori and lapilli1    
which in falling through  the air have  
arranged themselves in tolerably regular
 layers upon the  sides of the cone4    
,illustration3 ,fig4 #ce4--,natural     
section or a ,volcanic ,cone in the     
,island of ,vulcano4    a4 ,crater4 b b4
 ,lava-streams4 c4 ,dykes which have    
clearly formed  the ducts1 through which
 the lava has risen to the crater4 d d4 
,stratified volcanic scori4 e4 ,talus of
 fallen materials4    ,in the second    
place1 we have lava-streams which have  

been ejected from  the crater or from   
fissures on the flanks of the cone1 and 
flowed down  its sides4 ,and thirdly1 we
 find masses of lava filling up cracks  
in  the cone2 these latter are called   
'dykes4' ,of these three kinds of       
structures most volcanic mountains are  
built up1 but in different  cases the   
part played by these several elements   
may be very unequal4  ,sometimes        
volcanoes consist entirely of           
fragmentary materials1 at  others they  
are made up of lavas only1 while in the 
majority of  cases they have been formed
 by alternations of fragmentary and     
fluid  ejections1 the whole being bound 
together by dykes1 which are masses of  
lava injected into the cracks formed    
from time to time in the sides of  the  
growing cone4    ,if we direct our      
attention in the first place to the     
fragmentary  ejections1 we shall find   
that they affect a very marked and      
peculiar  arrangement1 which is best    
exhibited in those volcanic cones       

composed  entirely of such materials4   
,sidenote3 ,,internal ,,structure ,,of  
,,volcanic ,,cones4    ,everyone who    
examines volcanoes for the first time   
will probably be  struck by the regular 
stratification of materials of which    
they are  composed4 ,thus the tuffs     
covering the city of ,pompeii are found 
to  consist of numerous thin layers of  
lapilli and volcanic dust1 perfectly    
distinct from one another1 and assuming 
even the arrangement which we  usually  
regard as characteristic of materials   
that have been deposited  from a state  
of suspension in water4 ,the fragmentary
 materials in  falling through the air  
are sorted1 the finer particles being   
carried  farther from the vent than the 
larger and heavier ones4 ,the force  of 
different volcanic outbursts also varies
 greatly1 and sometimes  materials of   
different character are thrown out      
during successive  ejections4 ,these    
facts will be illustrated by fig4 #cf1  
which is a  drawing of a section exposed

 in a quarry opened in the side of the  
,kammerbhl4 ,in this section we see that
 the falling scori have been  arranged  
in rudely parallel beds1 but the regular
 deposition of these  has been          
interrupted by the ejection of masses of
 burnt slate torn from  the side of the 
vent1 probably during some more than    
usually violent  paroxysm of the        
volcano4 ,in those volcanoes which are  
built up of tuffs  and materials which  
have fallen in the condition of a muddy 
paste1 the  perfect stratification of   
the mass is often very striking indeed1 
and  large cones are found built up of  
thin uniformly-spread layers of more  or
 less finely-divided materials1 disposed
 in parallel succession4  ,such         
finely-stratified tuff-cones abound in  
the district of the ,campi  ,phlegri4   
,illustration3 ,fig4 #cf4--,section in  
the side of the ,kammerbhl1 ,bohemia4   
a a4 stratified basaltic scori4 b b4    
,bands made up of fragments  of burnt   
slate4 c4 ,stratified basaltic scori4 d 

d4 ,pseudo-dykes  occupying lines of    
fault4    ,sidenote3 ,,arrangement ,,of 
,,fragmental ,,materials4    ,if1 in    
consequence of any subterranean         
movements1 fissures are produced  in the
 sides of the cones formed of           
fragmentary materials1 these often      
become gradually filled with loose      
fragments from the sides of the         
fissure1 and in this manner             
'pseudo-dykes' are formed4 ,an example  
of  such pseudo-dykes is represented in 
fig4 #cf1 where the beds composing  the 
volcanic cone of the ,kammerbhl are seen
 to have been broken across  or faulted1
 and the fissures produced in the mass  
have been gradually  filled with loose  
fragments4    ,it is not difficult to   
imitate1 on a small scale1 the          
conditions which  exist at those        
volcanic vents from which only          
fragmentary materials  are ejected4 ,if 
we take a board having a hole in its    
centre1 into  which a pipe is inserted  
conveying a strong air-blast1 we shall1 

by  introducing some light material like
 bran or sawdust into this pipe  cause  
an ejection of fragments1 which will1   
when the board is placed  horizontally1 
fall around the orifice of the pipe and 
accumulate there  in a conical heap     
7fig4 #cg74 ,it will be found necessary1
 as was shown  by ,mr4 ,woodward1 who   
performed the experiment before the     
,physical  ,society1 to adopt some      
contrivance1 such as a screw1 for       
forcing the  material into the air-pipe4
 ,if we alternately introduce materials 
of  different colours1 like mahogany-   
and deal-sawdust into the pipe1 these   
materials will be arranged in layers    
which can be easily recognised1  and the
 mode of accumulation of the mass will  
be evident4 ,by means of  a sheet of tin
 or cardboard we may divide this        
miniature volcanic cone  vertically into
 two portions1 and if we sweep one of   
these away the  internal structure of   
the other half will be clearly displayed
 before  our eyes4    ,in this way we   

shall find that the conical heap of     
sawdust with the  hole in its centre has
 a very peculiar and definite           
arrangement of its  materials4 ,it is   
made up of a number of layers each of   
which slopes in  opposite directions1   
towards the centre of ejection and away 
from that  centre4 ,these layers are    
thickest along the line of the circle   
where  the change in slope takes place1 
and they thin away in the direction of  
the two opposite slopes4                
,illustration3 ,fig4                    
#cg4--;,experimental illustration of the
 mode of  ,formation of ,volcanic ,cones
 composed of fragmental materials4      
,sidenote3 ,,cause ,,of ,,this          
,,arrangement4    ,the cause of this    
peculiar arrangement of the materials is
 evident4  ,the sawdust thrown up by the
 air blast descends in a shower and     
tends  to accumulate in a circular heap 
around the orifice1 the area of this    
circular heap being determined by the   
force of the blast4 ,within this        

circular area1 however1 the quantity of 
falling fragments is not  everywhere the
 same2 along a circle surrounding the   
vent at a certain  distance1 the maximum
 number of falling fragments will be    
found to  descend1 and here the thickest
 deposit will take place4 ,as this goes 
on1 a circular ridge will be formed1    
with slopes towards and away  from the  
centre of injection4 ,as the ridge      
increases in height1 the  materials will
 tend to roll down either one slope or  
the other1 and  gradually a structure of
 the form shown in the figure will be   
piled up4  ,the materials sliding down  
the outer slope will tend to increase   
the  area of the base of the cone1 while
 those which find their way down the    
inner slope will fall into the vent to  
be again ejected4    ,illustration3     
,fig4 #ch4--,natural section of a       
,tuff-cone forming the  ,cape of        
,misenum1 and exhibiting the peculiar   
internal ,arrangement  characteristic of
 volcanoes composed of fragmentary      

materials4    ,volcanic cones composed  
of scori1 dust1 c4 are found to have    
exactly  the same internal structure as 
is exhibited by the miniature cone of   
sawdust4 ,the more or less regular      
layers of which they are made up dip  in
 opposite directions1 away from and     
towards the vent1 and thin out  in the  
direction of their dip 7see fig4 #ch74  
,in small cones the crater  or central  
cavity is of considerable size in       
proportion to the whole  mass1 but as   
the cone grows upwards and outwards1 the
 dimensions of  the crater remain the   
same1 while the area of the base and the
 height  of the cone are continually    
increasing4 ,this is the normal         
structure  of volcanic cones formed of  
fragmentary materials1 though1 as we    
shall  hereafter show1 many             
irregularities are often produced by    
local and  temporary causes4            
,illustration3 ,fig4 #ci4--,section of a
 small ,scoria-cone formed within  the  
crater of ,vesuvius in the year #ahhe1  

illustrating the filling-up of  the     
central tent of the cone by subsequent  
ejections4    ,in some cases the central
 vent of a volcanic scoria-cone may be  
filled up by subsequent ejections4 ,a   
beautiful example of this kind  was     
observed by ,abich1 in the case of a    
small cone formed within the  crater of 
,vesuvius in #ahce1 and is represented  
in fig4 #ci4    ,illustration3 ,fig4    
#dj4--,volcanic ,cones composed of      
,scori1 and  breached on one side by the
 outflow of lava-currents4    ,sidenote3
 ,,breached ,,cones4    ,many cones     
formed in the first instance of scori1  
tuff1 and pumice may  give rise to      
streams of lava1 before the vent which  
they surround sinks  into a state of    
quiescence4 ,in these cases1 the liquid 
lava in the vent  gives off such        
quantities of steam that masses of froth
 or scori are  formed1 which are ejected
 and accumulate around the orifice4     
,when the  force of the explosive action
 is exhausted1 the lava rises bodily in 

the crater1 which it more or less       
completely fills4 ,but1 eventually1  the
 weaker side of the crater-wall yields  
beneath the pressure of the  liquid     
mass1 and this part of the crater and   
cone is swept away before  the advancing
 lava-stream4 ,examples of such         
'breached cones' abound in  ,auvergne   
and many other volcanic districts 7see  
fig4 #dj74 ,a beautiful  example of a   
cone formed of pumice1 which has been   
breached by the  outflow of a           
lava-stream of obsidian1 occurs in the  
,lipari ,islands1 at  the ,rocche       
,rosse4 ,it is this locality which      
supplies the whole world  with pumice   
7see fig4 #da74    ,illustration3 ,fig4 
#da4--;,campo ,bianco1 in the ,island of
 ,lipari4 ,a  ,pumice-cone breached by  
the ,outflow of an ,obsidian            
,lava-current4    ,it is often          
surprising to find how volcanic cones   
composed of loose  materials1 such as   
tuffs1 scori1 or pumice1 retain their   
distinctive  forms1 and even the        

sharpness of their outlines1 during     
enormous  periods of time4 ,thus1 in the
 scoria-cones which abound in the       
,auvergne1 and were1 in all probability1
 formed before the historical  period1  
the sharp edges of the craters appear to
 have suffered scarcely  any erosion1   
and the cones are as perfect in their   
outlines as though  formed but          
yesterday4 ,it is probable that the     
facility with which these  cindery heaps
 are penetrated by the rain which falls 
upon them is the  cause why they are not
 more frequently washed away4           
,illustration3 ,fig4 #db4--,volcanic    
,cones in ,auvergne which have suffered 
to some extent from atmospheric         
denudation4    ,sometimes1 however1     
scoria-cones are found reduced by       
atmospheric  waste to mere heaps of     
cinders1 in which the position of the   
crater is  indicated only by a slight   
depression1 as in fig4 #db4             
,sidenote3 ,,cones ,,composed ,,of      
,,lava4    ,when but little explosive   

action takes place at the volcanic vent1
 and  only fluid lava is ejected1       
mountains are formed differing very     
greatly  in character from the cones    
composed of fragmentary materials4      
,if the lavas be of very perfect        
liquidity1 like those erupted in the    
,sandwich ,islands1 they flow outwards  
around the vent to enormous  distances4 
,by the accumulation of materials during
 successive  outbursts1 a conical mass  
is built up which has but a slight      
elevation  in proportion to the area of 
its base4 ,thus in ,hawaii we find great
  volcanic cones1 composed of very fluid
 lavas1 which have a height of  nearly  
#ad1jjj feet with a diameter of base of 
seventy miles4 ,in these  ,hawaiian     
mountains the slope of the sides rarely 
exceeds #f to #h4    ,but if1 on the    
other hand1 the lavas be of much more   
viscid  consistency1 the character of   
the volcanic cones which are produced by
  their extrusion will be very          
different4 ,the outwelling material will

  tend to accumulate and heap itself up 
around the vent4 ,by successive         
ejections the first-formed shell is     
forced upwards and outwards1 and  a     
steep-sided protuberant mass is formed1 
exhibiting in its interior  a marked    
concentric arrangement4 ,dr4 ,ed4       
,reyer1 of ,grtz1 has devised  a very   
ingenious method for reproducing on a   
miniature scale the  characteristic     
features of these eruptions of viscid   
lavas4 ,he takes a  quantity of plaster 
of ,paris reduced to a pasty            
consistence1 which he  forces through a 
hole in a board4 ,the plaster           
accumulates in a great  rounded boss    
about the orifice through which it has  
been forced4 ,if the  plaster have some 
colouring matter introduced into it1 the
 mass1 on  being cut across1 will       
exhibit in the disposition of its       
colour-bands  the kind of action which  
has gone on during its extrusion1 fig4  
#dc4    ,illustration3 ,fig4            
#dc4--;,experimental illustration of the

 ,mode of  ,formation of volcanic cones 
composed of viscid lavas4               
,illustration3 ,fig4 #dd4--,the ,grand  
,puy of ,sarcoui1 composed of  trachyte1
 rising between two breached            
scoria-cones 7,auvergne74    ,there are 
many volcanic cones which exhibit clear 
evidence of having  thus been formed by 
the extrusion of a viscid mass of lava  
through  a volcanic fissure4 ,among such
 we may mention the domitic ,puys of    
,auvergne1 fig4 #dd1 many andesitic     
volcanoes in ,hungary1 the phonolite    
hills of ,bohemia1 and the so-called    
'mamelons' of the ,island of  ,bourbon4 
,see figs4 #de and #df4 ,when the       
interior of these masses is  exposed by 
natural or artificial sections1 they are
 all found to  exhibit the onion-like   
structure which occurs in the plaster   
models4    ,sidenote3 ,,internal        
,,structure ,,of ,,lava-,,cones4        
,illustration3 ,fig4 #de4--,volcanic    
,cone 7,mamelon7 composed of very       
viscid lava4 7,island of ,bourbon47     

,illustration3 ,fig4 #df4--;,another    
,mamelon in the ,island of ,bourbon1    
with  a crater at its summit4    ,but   
while some volcanoes are composed       
entirely of the fragmentary  ejections  
and others are wholly formed by         
successive outflows of lava1  the       
majority of volcanoes1 especially those 
of larger dimensions1 are  built up of  
alternations of these different kinds of
 materials4    ,illustration3 ,fig4     
#dg4--;,cliff-section in the ,island of 
,madeira1  showing how a composite      
volcano is built up of lava-streams1    
beds of  scori1 and dykes4    ,sidenote3
 ,,natural ,,sections ,,of ,,cones4     
,the structure of these composite cones 
may be understood by an  inspection of  
the accompanying fig4 #dg1 which shows  
the appearances  presented in a cliff on
 the coast of the ,island of ,madeira4  
,we see  that the mass is made up of    
numerous layers of volcanic scori1      
alternating with sheets of lava4 ,the   
latter1 which are represented  in       

transverse section in the drawing1 are  
seen to thin out on either  side1 and to
 vary greatly in breadth4 ,besides the  
alternating masses  of scori and the    
lava-sheets1 there are seen in the      
section1 bands  of a bright-red colour1 
which are represented in the drawing by 
black  lines4 ,these are layers of soil1
 or volcanic dust1 which1 by the        
passage of a lava-stream over their     
surface1 have been burnt so as  to      
acquire a brick-red colour4 ,these bands
 of red material1 to which  the name of 
'laterite' has been frequently applied1 
very commonly  occur in sections of     
composite volcanic cones4 ,crossing the 
whole of  the horizontally-disposed     
masses in the section1 we find a number 
of  'dykes1' which are evidently great  
cracks filled with lava from below4     
,some of these run vertically through   
the cliffs1 others obliquely4 ,in  some 
cases the lava1 rising to fill a dyke1  
has flowed as a lava-stream  at the     
surface4 ,last of all1 we must call     

attention to the fact that  the section 
exhibits evidence of great movements    
having taken place  subsequently to the 
accumulation of the whole of the        
materials4 ,a  great crack has been     
produced1 on one side of which the whole
 mass has  subsided bodily1 giving rise 
to the phenomenon which geologists call 
a  'fault4'    ,in the section1 fig4    
#bg1 p4 #ajd1 copied from a drawing of a
 sea-cliff  in the ,island of ,vulcano1 
a transverse section of a lava-stream is
  represented on a somewhat larger      
scale4 ,the upper and under surface of  
the lava-stream is seen to have a       
scoriaceous structure1 but the thick    
central mass is compact1 and divided by 
regular joint-planes4 ,this  section    
also illustrates the fact that1 before  
the lava-stream flowed  down the sides  
of the mountain1 a valley had been cut  
by meteoric  agencies on the flanks of  
the volcano1 the dykes which traverse   
the  lower beds of tuff being abruptly  
truncated4    ,in mountain ravines1 upon

 the slopes of ancient volcanoes1 and in
 the  cliffs of volcanic islands1 we are
 often able to study the way in which   
these great mountain masses are built up
 of alternating lava-currents1  beds of 
volcanic agglomerate1 scori1 tuff and   
dust1 and intersecting  dykes4 ,in fig4 
#dh1 the features above described are   
illustrated by a  section in the sides  
of the great volcano of ,mont ,dore4    
,illustration3 ,fig4 #dh4--,section seen
 at the cascade4 ,bains du ,mont  ,dore4
    ,illustration3 ,fig4 #di4--,section 
in the ,island of ,ventotienne1 showing 
a great stream of andesitic lava        
overlying stratified tuffs4             
,sidenote3 ,,sections ,,in ,,the ,,ponza
 ,,islands4    ,in figs4 #di1 #ej1 #ea1 
and #eb1 we have given drawings of      
portions of the  sea-cliffs in several  
of the ,ponza ,islands1 a small volcanic
 group off  the ,italian coast4         
,illustration3 ,fig4 #ej4--;,cliff on   
the south side of the ,island of ,san   
,stephano4    a4 ,trachyte lava-stream1 

with a scoriaceous upper surface        
overlaid by  stratified tuffs1 b4       
,illustration3 ,fig4 #ea4--,the headland
 of ,monte della ,guardia1 in the       
,island of ,ponza4    a4 ,columnar      
trachyte4 b4 ,stratified tuffs4 c4      
,pumiceous  agglomerates4 d4 ,dyke of   
rhyolite4    ,illustration3 ,fig4       
#eb4--,western side of the same         
headland1 as seen  from the north side  
of ,luna ,bay4    a4 ,trachyte lava4 b4 
,stratified tuffs4 c4 ,dykes of         
rhyolite1 with  their edges passing into
 pitchstone4 d4 ,pumiceous agglomerate4 
,illustration3 ,fig4 #ec4--,sea-cliff at
 ,il ,capo1 the north-east point of     
,salina showing stratified agglomerates 
traversed by numerous dykes1 the  whole 
being unconformably overlaid by         
stratified aqueous deposits4    ,fig1   
#ec represents a cliff-section in the   
island of ,salina1 one of the  ,liparis1
 exhibiting evidence that a series of   
volcanic agglomerates  traversed by     
dykes of ,andesite have been denuded and

 covered by a  recent stratified        
deposit4    ,sidenote3 ,,part ,,played  
,,by ,,dykes ,,in ,,cone-,,building4    
,in the formation of these great        
composite cones1 a minor but by no      
means insignificant part is played by   
the dykes1 or lava-filled  fissures1    
which are seen traversing the mass in   
all directions4 ,that  dyke-fissures    
often reach the surface of a volcanic   
cone1 and that  the material which      
injects them then issues as a           
lava-stream1 is  illustrated by fig4    
#ed4 ,the formation of these cracks in a
 volcanic  cone1 and their injection by 
liquid lava1 must of course distend  the
 mountainous mass and increase its      
volume4 ,if we visit the great          
crater-walls of ,somma in ,vesuvius1 and
 of the ,val del ,bove in ,etna1  we    
shall find that the dykes are so        
numerous that they make up a            
considerable portion of the mass4 ,when 
the loose scori and tuffs are  removed  
by denudation1 these hard dykes often   

stand up prominently like  great walls1 
as represented in fig4 #ee4 ,even in    
such cases as these1  however1 it is    
doubtful whether the bulk of all the    
dykes put together  exceeds one-tenth of
 that of the lavas and fragmentary      
materials4    ,illustration3 ,fig4      
#ed4--,section observed in the ,val del 
,bove1 ,etna1  showing a basaltic dyke1 
from the upper part of which a          
lava-current  has flowed4               
,illustration3 ,fig4 #ee4--;,basaltic   
,dykes projecting from masses of        
stratified scori in the sides of the    
,val del ,bove1 ,etna4    ,hence we are 
led by an examination of the internal   
structure of  volcanic mountains to     
conclude that scori- and tuff-cones1 and
 cones  formed of very liquid lavas1    
increase by an exogenous mode of growth1
  all new materials being added to them 
from without2 in the cones formed  of   
very viscid lavas1 on the other hand1   
the growth is endogenous1  taking place 
by successive accretions within it4 ,the

 composite cones  owe their origin to   
both the exogenous and the endogenous   
modes of  growth1 but in a much greater 
degree to the former than the latter4   
,the  layers of scori1 tuff1 and dust1  
and the successive lava-streams are     
added to the mass from without1 and the 
lava forming the dykes from  within it4 
,sidenote3 ,,theory ,,of ,,elevation    
,,craters4    ,there are doubtless cases
 in which1 when a tuff-cone is formed1 a
 mass  of very viscid lavas is extruded 
into its interior1 and the mass is      
distended like a gigantic bubble4 ,but  
inasmuch as the very viscid lavas  do   
not appear to give rise to scori to     
anything like the same extent  as the   
more liquid kinds1 such 'cupolas1' as   
they have been called  by some ,german  
geologists1 are probably not very       
numerous1 and may  be regarded as       
constituting the exception rather than  
the rule4 ,the  idea which was formerly 
entertained by some geologists that all 
great  volcanic mountains were formed of

 masses originally deposited in a       
horizontal position1 and subsequently   
blown up into a conical form1 has  been 
effectually disposed of by the          
observations of ,lyell and ,scrope4     
,the condition of the great fluid masses
 which underlie volcanic vents  is      
another point on which much light has   
been thrown by the study  of            
naturally-dissected volcanoes4 ,in some 
cases1 as was shown by  ,hochstetter    
during his admirable researches among   
the ,new ,zealand  volcanoes1 the rising
 lavas form a great chamber for         
themselves in the  midst of a volcanic  
cinder-cone1 taking the place of loose  
materials  which are re-ejected from the
 vent1 or have been re-fused and        
absorbed  into the mass of lava itself4 
,from this central reservoir of lava1   
eruptions are kept up for some time1 but
 when the volcano sinks  into a state of
 quiescence the lava slowly             
consolidates4 ,in such  slowly          
solidified masses of lava1 very         

beautiful groups of radiating  columns  
are often exhibited ,northern ,germany  
abounds with examples  of such basaltic 
masses1 which have once formed the      
centres of great  cinder-cones2 but in  
consequence of the removal of the loose 
materials  and the surrounding strata by
 denudation1 these central reservoirs of
  the volcanoes have been left standing 
above the surface1 and exhibit  the     
peculiar arrangements of the columns    
formed in them during the  process of   
cooling4    ,sidenote3 ,,intrusive      
,,lava-,,sheets4    ,but in the majority
 of the more solidly-built composite    
volcanoes no  such liquid reservoir can 
be formed within the volcanic cone      
itself4  ,under these circumstances1 the
 lavas1 especially those of more liquid 
character1 tend to force passages for   
themselves among the rocks  through     
which they are extruded4 ,wherever a    
weak point exists1 there  such lavas    
will find their way1 and as the planes  
of stratification  in sedimentary rocks 

constitute such weak places1 we         
constantly find  sheets of lava thus    
inserted between beds of aqueous origin4
 ,the areas  over which these intrusive 
sheets of rock sometimes extend may be  
very  great1 but the more fusible1 basic
 lavas 7basalt1 c47 usually form  much  
more widely-spreading sheets than the   
less fusible1 acid lavas4  ,in some     
cases these great intrusive sheets are  
found extending to a  distance of twenty
 or thirty miles from the centre at     
which they were  ejected1 and they often
 follow the bedding of the strata with  
which  they are intercalated in so      
regular a manner1 that it is difficult  
for  an observer to believe at first    
sight that they can have been formed in 
the way which we have described4 ,a     
closer examination will generally       
reveal the fact that while these        
intrusive lava-sheets retain their      
parallelism with the strata among which 
they have been intruded1 over           
considerable areas1 yet they sometimes  

break across1 or send offshoots  into   
them1 as shown in fig4 #ef4 ,in all     
cases1 too1 the rocks lying  above and  
below such sheets will be found to be   
more or less baked and  altered1 and    
this affords a very convincing evidence 
of the intrusion  of the igneous mass   
between the strata so altered4          
,illustration3 ,fig4 #ef4--,sheets of   
,igneous ,rock 7,basalt7 intruded       
between beds of sandstone1 clay1 and    
limestone4 7,island of ,skye47    ,that 
in the case of most great volcanic      
mountains1 or systems of  mountains1    
vast reservoirs of liquid lava must     
exist in the earth's  crust far below   
the surface1 there can be little room   
for doubt4  ,whether such fluid masses  
are in direct or indirect communication 
with  a great central reservoir1 even   
supposing such to exist1 is a totally   
different question4 ,in many cases the  
outburst of volcanoes in more or  less  
close proximity has been observed to    
take place simultaneously1  while in    

others the commencement of the eruption 
of one volcano has  coincided with the  
lapse into quiescence of another in its 
vicinity4  ,on the other hand1 the      
remarkable case of the volcanoes of     
,hawaii  seems to indicate that two     
vents in close proximity may be supplied
  from perfectly distinct reservoirs of 
lava4 ,the active craters of  ,mauna    
,loa and ,kilauea are situated at the   
heights of #ad1jjj and #d1jjj  feet     
respectively above the sea level2 yet   
the former is sometimes  in a state of  
violent activity1 with which the latter 
shows no signs  of sympathy whatever4   
,we shall1 in a future chapter1 adduce  
evidence  that the liquid lavas in      
underground reservoirs may undergo      
various  stages of change in the        
enormous periods of time during which   
habitual  volcanic vents are supplied   
from them4    ,we have already shown    
that the character assumed by a mass of 
fused  material in cooling varies       
greatly according as the cooling takes  

place  rapidly at the surface or slowly 
under enormous pressure4 ,in the former 
case a glassy base is formed containing 
a greater or smaller number  of         
crystallites or embryo crystals1 in the 
latter the whole rock is  converted into
 a mass of fully-developed crystals4    
,sidenote3 ,,consolidation ,,of ,,lavas 
,,at ,,great ,,depths4    ,the lavas    
which are poured out at the surface     
consist1 as we have  seen1 of a glassy  
magma in which a greater or smaller     
number of  crystals are found which have
 been borne up from below4 ,the great   
dykes and intrusive sheets consist for  
the most part of a mass of  small or    
imperfectly developed crystals in which 
a number of large and  perfectly formed 
crystals are embedded4 ,such rocks are  
said to have a  'porphyritic' structure4
 ,the rocks formed by the consolidation 
of the  liquid masses in the underground
 reservoirs are found to be perfectly   
crystallised1 the crystals impressing   
one another on every side and  making up

 the whole mass to the exclusion of any 
paste or magma between  them4 ,the      
crystals in those rocks which have      
consolidated at these  vast depths      
exhibit evidence1 in their enclosed     
watery solutions and  liquefied carbonic
 acid1 of the enormous pressures under  
which they  must have been consolidated4
 ,the lavas1 the more or less           
porphyritic  rocks of the dykes and     
sheets1 and the perfectly crystalline   
7granitic7  rocks of the underground    
reservoirs pass into one another1       
however1 by  the most insensible        
gradations4    ,we sometimes find       
examples of volcanoes which1 by the     
action of  denuding forces1 have had    
their very foundations exposed to our   
view4  ,such examples occur in the      
,western ,isles of ,scotland1 in the    
,euganean  ,hills near ,padua in        
,northern ,italy1 and in many other     
parts of the  earth's surface4 ,in these
 cases we are able to trace the         
ground-plan of  the volcanic pile1 and  

to study the materials which have       
consolidated  deep beneath the surface  
in the very heart of the mountain4      
,in studying these 'basal wrecks' of old
 volcanoes it is always  necessary to   
bear in mind that the appearance and    
general characters of  a volcanic rock  
may be completely disguised by chemical 
changes going  on within it4 ,it is     
through want of attention to this fact  
that so many  mistakes were made by the 
,wernerian school of geologists who     
declared  that they could find no       
analogy between the basaltic rocks of   
the globe  and the products of active   
volcanoes1 and were hence led to refer  
the  origin of the former to some kind  
of 'aqueous precipitation4'    ,many of 
the hard and crystalline marbles which  
are employed as  ornamental stones were 
originally loose masses of shells and   
corals1  as we easily perceive when we  
examine the polished faces4 ,but these  
incoherent heaps of organic dbris have  
been converted into a compact  and solid

 rock in consequence of the mass being  
penetrated by water  containing         
carbonate of lime in solution4 ,crystals
 of this substance  were deposited in   
every cavity and interstice of the mass1
 and thus  the accumulation of separate 
organisms was gradually transformed to a
  material of great solidity and        
hardness4    ,sidenote3 ,,formation ,,of
 ,,amygdaloids4    ,in precisely the    
same way loose heaps of scori1 lapilli1 
or pumice  may1 by the passage through  
them of water containing various        
substances  in solution1 have their     
vesicles filled with crystals1 and thus 
be  converted into the hardest and most 
solid of rock-masses4 ,similarly  the   
scoriaceous portions of lava-streams    
have their vesicles filled  with        
crystalline substances deposited from a 
state of solution1 and  are thus        
converted into a solid mass which may at
 first sight appear  to offer but little
 resemblance to the vesicular materials 
of recent  lava-streams4 ,to these      

vesicular rocks which have their        
cavities filled  with crystalline       
substances geologists apply the name of 
amygdaloids  7,l4 amygdalus1 an almond74
 ,the cavities in lava-rocks are usually
  more or less elongated1 owing to the  
movement of the mass while in  a still  
plastic state1 and the crystalline      
materials filling these  cavities take  
the almond-like shape2 hence the name4  
,when the amygdaloids and altered       
fragmentary ejections of volcanoes  are 
studied microscopically1 their true     
character is at once made  manifest4    
,the exposure of faces of these altered 
volcanic rocks to the  weathering       
influences of the atmosphere1 in many   
cases also causes  their true nature to 
be revealed1 the crystalline materials  
filling  the interstices and vesicles of
 the mass are dissolved away by the     
rain-water containing carbonic acid1 and
 the rock regains its original          
cavernous structure and appearance4 ,but
 this repeated passage of water  through

 volcanic rock-masses may result in the 
removal of so large a  portion of their 
materials that the remainder crumbles   
down into the  condition of a clay or   
mud4    ,in the basal wrecks of         
volcanoes1 of which we have spoken1 we  
usually  find only small and fragmentary
 remains of the great accumulations  of 
loose and scoriaceous materials which   
originally constituted the  bulk of the 
mountain mass4 ,in the centre of the    
ground-plan of such  a denuded volcano  
we find great masses of highly          
crystalline or  granitic rock1 which    
evidently occupy vast fissures broken   
through  the sedimentary or other rocks 
upon which the volcanic pile has been   
reared4 ,these highly crystalline rocks 
exhibit1 as we have shown1  clear       
evidence of having been consolidated    
from a state of fusion  with extreme    
slowness and under enormous pressure1   
but their ultimate  chemical composition
 is identical with that of the lavas    
which have  been ejected from the       

volcano4    ,when1 as frequently        
happens1 the volcano1 after pouring out 
one kind  of lava for a certain period1 
has changed the nature of its ejections1
  and given rise to materials of        
different composition1 we find clear    
evidence of the fact in studying the    
basal wreck or ground-plan of  the      
volcano4 ,a great intrusive crystalline 
mass1 of the same chemical  composition 
as the first-extruded lava1 is found to 
be rent asunder and  penetrated by a    
similarly crystalline mass having the   
composition of  the lavas of the second 
period4 ,thus1 in the volcanoes of the  
,western  ,isles of ,scotland1 which are
 reduced by the action of denudation to 
this condition of basal wrecks1 we find 
that rhyolites1 trachytes1 and          
andesites were ejected during the       
earlier periods of their history1 and   
basalts during the later periods4       
,illustration3 ,fig4 #eg4--,plan of the 
,dissected ,volcano of ,mull1 in the    
,inner ,hebrides4    ,illustration3     

a ,rocks on which the ,volcano has been 
built up4    b ,great intrusive masses  
of acid and intermediate rocks4    c    
,lara currents of basalt which have     
flowed from d4    d ,intrusive masses of
 gabbros  dolerite4    e ,lava currents 
which have flowed from b4    f ,volcanic
 tuffs and agglomerates4    ,fig4       
#eh4--,section of the ,volcano along the
 line ,a ,b4    ,sidenote3 ,,ancient    
,,volcano ,,of ,,mull4    ,we perceive  
on studying the ground-plan of these    
volcanoes that  great masses of granite1
 syenite1 and diorite--the crystalline  
representatives of the first-extruded   
lavas--are penetrated by  intrusions of 
gabbro--the granitic form of the        
later-ejected lavas4  ,these features   
are admirably illustrated by the ruined 
volcano now  constituting the ,island of
 ,mull1 one of the ,inner ,hebrides1 a  
plan  of which is given in fig4 #eg1 and
 a section in fig4 #eh4 ,this volcano   
probably had a diameter at its base of  
nearly thirty miles1 and a  height of   

from #aj1jjj to #ab1jjj feet1 but is now
 reduced to a group of  hills few of    
which exceed #c1jjj feet in height4     
,from these great intrusive masses of   
highly crystalline rocks there  proceed 
in every direction great spurs or dykes1
 which are evidently  the radiating     
fissures formed during the outwelling of
 igneous  materials from below1 injected
 by these fluid substances4 ,the rock   
forming these dykes is often less       
perfectly crystalline than that which   
constitutes the centre of the mass1 and 
we may indeed detect among the          
materials of these dykes examples of    
every variety of structure1 from  the   
perfectly crystalline granite to the    
more or less glassy substance  of lavas4
 ,besides the vertical or oblique dykes 
we also find horizontal  sheets1 which1 
passing from these central masses1 have 
penetrated  between the surrounding     
strata1 often1 as we have seen1 to      
enormous  distances4    ,for the sake of
 simplicity1 we have spoken of these    

ground-plans1 or  basal wrecks of       
volcanoes1 as constituting a flat plain2
 as a matter of  fact1 however1 the     
unequal hardness of the materials       
composing volcanic  mountains causes    
them to assume1 under the influence of  
denuding  agencies1 a very rugged and   
uneven surface4 ,the hard crystalline   
materials filling the central vent stand
 up as great mountain groups2  each     
large dyke1 by the removal of the       
surrounding softer materials1 is  left  
as a huge wall-like mass1 while the     
remnants of lava-streams are  seen      
constituting a number of isolated       
plateaux4    ,the great ,island of ,skye
 is the basal wreck of another volcano  
which  was also in eruption during      
,tertiary times2 probably1 many millions
  of years ago4 ,this immense volcano   
had originally a diameter at its  base  
of about thirty miles1 and a height of  
#ab1jjj to #ae1jjj feet1  and must have 
been comparable to ,etna or ,teneriffe  
in its dimensions4  ,at the present     

time1 there is nothing left of this vast
 pile but the  highly crystalline       
granites and gabbros filling up the     
great fissures  through which the       
eruption of igneous materials took      
place4 ,these1 worn  by denudation into 
rounded dome-like masses and wild rugged
 peaks1  constitute the ,red ,mountains 
and ,coolin ,hills of ,skye1 which rise 
to  the height of more than #c1jjj feet 
above the sea-level4 ,from these  great1
 central masses of crystalline rocks1   
innumerable radiating dykes  may be     
found rising through the surrounding    
rock-masses1 with isolated  patches of  
the scori and lapilli ejected from the  
volcano1 which have  here and there     
escaped removal by denudation4 ,along   
what were the  outskirts of this great  
mountain-mass are found flat-topped     
hills1  built up of lava-streams1 only  
small portions of which have escaped    
removal by denudation4    ,sidenote3    
,,reservoirs ,,beneath ,,volcanoes4     
,but this wearing away of the structure 

of a volcanic cone by the  denuding     
forces may proceed even one stage       
farther1 and we may then  have revealed 
for our inspection and study the mass of
 originally fluid  materials1 from which
 one or more volcanoes have been fed1   
cooled and  consolidated in their       
original reservoir4 ,there are many     
examples of  masses of granitic or      
highly crystalline rocks1 having        
precisely the  same composition as the  
different varieties of lavas1 which are 
found  lying in the midst of the        
sedimentary rocks1 and sending off into 
these rocks veins and dykes of the same 
composition with themselves4  ,no one   
who has carefully studied the           
appearances presented by volcanic       
mountains in different stages of        
dissection1 by the action of denuding   
forces1 can avoid recognising these     
great granitic masses as the cooled     
reservoirs from which volcanoes have in 
all probability been supplied  during   
earlier periods of the earth's history4 

,the eruption of these great masses of  
incandescent rock1 impregnated  with    
water and acid gases1 through strata of 
limestone1 sandstone1  clay1 coal1 c41  
may be expected to produce striking and 
wonderful  chemical changes in the      
latter4 ,nor are we disappointed in     
these  anticipations4 ,whenever we      
examine the sedimentary materials around
  volcanic vents1 we find that1 in      
contact with the once-fused materials1  
they everywhere exhibit remarkable      
evidences of the chemical action  to    
which they have been subjected4 ,the    
limestones are converted into  statuary 
marble1 the sandstones pass into        
quartzite1 the days assume  the hardness
 and lustre of porcelain1 while the     
coals have lost their  volatile         
ingredients and assumed a form like coke
 or graphite4 ,and  these changes are   
found to extend in many cases to the    
distance of many  hundreds of yards from
 the planes of junction between the     
igneous and  the sedimentary materials4 

,among the most interesting effects     
resulting from the extrusion of  masses 
of incandescent rock1 charged with water
 and various gases1  through beds of    
limestone1 clay1 sandstone1 c41 we may  
mention the  production of those        
beautiful crystalline minerals which    
adorn our  museums and are so highly    
prized as gems4 ,by far the larger part 
of  these beautiful minerals have been  
formed1 directly or indirectly1 by      
volcanic agencies4    ,these gems and   
beautiful minerals are1 for the most    
part1 substances  of every-day          
occurrence1 which entirely owe their    
beauty to the  crystalline forms they   
have assumed4 ,the diamond is           
crystallised  carbon1 the ruby and      
sapphire are crystallised alumina1 the  
amethyst  and a host of other gems are  
crystallised silica2 and in almost all  
cases the materials of gems are common  
and widely diffused1 it is only  in     
their finely crystalline condition that 
they are rare and therefore  valuable4  

,sidenote3 ,,formation ,,of ,,volcanic  
,,minerals4    ,crystals are formed     
during the slow deposition of a         
substance1 either  by the evaporation of
 a liquid in which it is dissolved1 by  
its  volatilisation1 or its cooling from
 a state of fusion4 ,in many cases it   
can be shown that the formation of large
 and regular crystals is aided  if the  
work goes on with extreme slowness and  
under great pressure4  ,by sealing up   
various substances in tubes containing  
water which can  be kept at a high      
temperature1 minute crystals of many    
well-known  minerals have been          
artificially formed by chemists4 ,part  
of the water  converted into steam has  
formed a powerful spring1 which1        
reacting  upon the remainder of the     
liquid in the tube1 has subjected it to 
enormous pressure1 and under these      
conditions of extreme pressure and      
temperature1 chemical actions take place
 of which we have no experience  under  
ordinary circumstances4 ,the experiments

 of ,mr4 ,hannay seem to  prove that    
when carbon is separated from certain   
organic substances  at a high           
temperature and under great pressure1 it
 may crystallise in  the form of the    
diamond4 ,and the recent discovery of   
diamonds in the  midst of materials     
filling old volcanic vents in ,south    
,africa seems  to show that this was in 
many cases the mode in which the gem was
  originated4 ,even under the conditions
 which prevail at the earth's  surface1 
however1 minute and unnoticed chemical  
actions taking place  during long       
periods of time1 produce most remarkable
 results4 ,this has  been well          
illustrated by ,m4 ,daubre1 who has     
shown that in the midst of  masses of   
concrete which the ,romans built up     
around the hot springs of  ,plombires   
and other localities1 many crystalline  
minerals have been  formed1 in the      
course of #b1jjj years1 by the action of
 the waters upon  the ingredients of the
 concrete4    ,but most of the crystals 

of minerals which have been thus        
artificially  formed are of minute1     
indeed often of microscopic1 dimensions4
 ,in the  underground reservoirs beneath
 volcanoes1 however1 we have all the    
necessary conditions for the formation  
of crystals of minerals on a  far       
grander scale4 ,high temperatures1      
pressures far greater than any  we can  
command at the earth's surface1 the     
action of superheated steam  and many   
acid gases on the various constituents  
of both igneous and  sedimentary rocks1 
and1 above all1 time of almost unlimited
 duration2  these constitute such a set 
of conditions as may fairly be expected 
to result in the formation of crystals1 
similar to those artificially  produced 
but of far greater size and beauty4     
,if we visit those parts of the earth's 
surface where great masses of  fused    
volcanic rock have slowly cooled down in
 contact with sedimentary  materials1 we
 shall not be disappointed in our       
expectations4 ,diamonds1  rubies1       

sapphires1 emeralds1 topazes1 garnets1  
and a host of equally  beautiful1 if    
less highly prized1 crystalline         
substances1 are found in  such          
situations1 lying in the subterranean   
chemical laboratories in  which they    
have been formed1 but now1 by the action
 of denuding forces1  revealed to our   
view4    ,in some cases it is not       
necessary to penetrate to these         
subterranean  laboratories in order to  
find these beautiful gems and other     
crystallised minerals2 for the steam    
jets which issue from volcanic  fissures
 carry up fragments of rock torn from   
the side of the vent1  and in the       
cavities and fissures of such ejected   
masses beautiful  crystallised products 
are often found4 ,such rock-fragments   
containing  minerals finely crystallised
 are found abundantly on the flanks of  
,vesuvius and other active volcanoes1   
and among the materials of the  ,laacher
 ,see and other extinct volcanoes4      
,sidenote3 ,,formation ,,of             

,,mineral-,,veins4    ,but it is not    
only the finely crystallised minerals   
and gems which  we owe to volcanic      
action4 ,the various metallic minerals  
have nearly  all been brought from      
deep-seated portions of the earth's     
crust and  deposited upon the sides of  
rock-fissures by the agency of the same 
volcanic forces4 ,it is these forces    
which have1 in the first instance1      
opened the cracks through the solid rock
 masses2 and1 in the second  place1 have
 brought the metallic sulphides1 oxides1
 and salts--either  in fusion1 in       
solution1 or in a vaporised             
condition--from the  deep-seated masses 
within the earth1 causing them to       
crystallise upon  the sides of the      
fissures1 and thus form those metallic  
lodes and veins  which are within reach 
of our mining operations4    ,there is  
still one other important class of      
minerals which owe the  existence1      
though indirectly1 to volcanic agencies4
 ,the cavities of  igneous rocks1       

especially the vesicles formed by the   
escape of steam1  constitute1 when      
filled with water1 laboratories in which
 complicated  chemical reactions take   
place4 ,the materials of the lava are   
gradually  dissolved and re-crystallised
 in new combinations4 ,by this means the
  most beautiful examples of such       
minerals as the agates1 the onyxes1  the
 rock-crystals1 the ,iceland-spars1 and 
the numerous beautiful  crystals classed
 together as ',zeolites' have been      
formed4 ,no one can  visit a large      
collection of crystalline minerals      
without being struck  with the large    
number of beautiful substances which    
have thus been  formed as secondary     
products from volcanic materials4       
,,chapter ,,vi4    ,,the ,,various      
,,structures ,,built ,,up ,,around      
,,volcanic ,,vents      ,from what has  
been said in the preceding chapters it  
will be seen that  while some of the    
materials ejected from volcanic vents   
are1 by the  movements of the air and   

ocean1 distributed over every part of   
the  face of the globe1 another1 and by 
far the larger1 part of the matter  so  
ejected1 accumulates in the immediate   
vicinity of the vent itself4  ,by this  
accumulation of erupted materials1      
various structures are  built up around 
the orifices from which the ejections   
take place1 and  the size and character 
of these structures vary greatly in     
different  cases1 according to the      
quantity and nature of the ejected      
materials1  and the intensity of the    
eruptive forces by which they were      
thrown from  the orifice4 ,we shall     
proceed in the present chapter to notice
 the  chief varieties in the forms and  
characters of the heaps of materials    
accumulated round volcanic vents4       
,these heaps of materials vary in size  
from masses no bigger than a  mole-heap 
up to mountains like ,etna1 ,teneriffe1 
and ,chimborazo4 ,the  size of volcanic 
mountains is principally determined by  
the conditions  of the eruptive action  

at the vent around which they are       
formed4 ,if  this action exhausts itself
 in a single effort1 very considerable  
volcanic cones1 like the ,monte ,nuovo  
with many similar hills in its          
vicinity1 and the ,puys of ,auvergne1   
may be formed2 but if repeated          
eruptions take place at longer or       
shorter intervals from the same vent1   
there appears to be scarcely any limit  
to the size of the structures  which    
may1 under such conditions1 be formed4  
,it is by this repeated  action from the
 same volcanic vent going on for        
thousands or even  millions of years1   
that the grandest volcanic mountains of 
the globe  have been built up4 ,such    
volcanoes have sometimes a diameter at  
their  base of from #cj to #ajj miles1  
and an elevation of from #aj1jjj to     
#be1jjj  feet4    ,the form of volcanic 
mountains is determined in part by the  
nature  of the materials ejected1 and in
 part by the character of the eruptive  
action4    ,from what has been said in  

the preceding chapter1 it will be       
gathered  that the volcanoes built up by
 ejections of fragmentary materials     
differ in many striking particulars from
 those formed by the outwelling  of     
lavas from volcanic vents4 ,in a less   
degree1 the volcanoes composed  of the  
same kind of volcanic materials also    
vary among themselves4    ,sidenote3    
,,characters ,,of ,,scoria-,,cones4     
,when masses of scori in a semi-fluid   
condition are thrown to only a  little  
distance above the volcanic vent1 so    
that they have not time to  assume a    
perfectly solid condition before they   
fall round the vent1 the  rugged masses 
of lava unite to form heaps of most     
irregular shape4 ,in  such cases1 the   
falling fragments being in a            
semi-plastic state1 stick  to the masses
 below1 and do not tend to roll down the
 sides of the  heap4 ,irregular heaps of
 such volcanic scori abound on the      
surfaces  of lava-streams1 being piled  
up around each 'bocca' or vent which the

  steam-jets escaping from the          
lava-currents form at their surfaces4   
,such irregular accumulations of scori  
were observed on the lavas of  ,vesuvius
 during the eruptions of #ahbb1 #ahee1  
and #ahgb1 and have also  been described
 in the case of many other volcanoes4   
,in fig4 #bf 7p4 #aja7  we have given   
representations of a group of such      
irregular scoria-cones  which was       
observed by ,schmidt on the ,vesuvian   
lava of #ahee4 ,it will  be seen from   
this drawing that there is scarcely any 
limit to the  steepness of the sides of 
such scoria-heaps1 in which the         
materials are  in an imperfectly        
solidified condition when they reach the
 ground4    ,but in the majority of     
cases1 the scori ejected from volcanic  
vents  are thrown to a great height1 and
 are in a more or less perfectly        
solidified condition when they fell to  
the ground again4 ,in such cases  the   
fragments obey the ordinary mechanical  
laws of falling bodies1  rolling and    

sliding over one another1 till they     
acquire a slope which  varies according 
to the size and form of the fragments4  
,in this way  the great conical mounds  
are formed which are known as           
'cinder-cones1'  or more properly as    
'scoria-cones4' ,scoria-cones usually   
vary in the  slope of their sides from  
#ce to #dj and may differ in size from  
mere  monticules to hills a thousand    
feet or more in height4 ,scoria-cones   
of this character abound in many        
volcanic districts1 as the ,auvergne1   
where they may be numbered by thousands4
 ,the materials forming such            
scoria-cones vary in size from that of a
 nut to masses as large as a  man's     
head1 and fragments of even larger      
dimensions are by no means  uncommon4   
,when the lava in a volcanic vent is    
perfectly glassy1 instead of being      
partially crystalline in structure1 we  
find not scori but pumice  ejected4 ,in 
such cases1 as in the ,lipari ,islands  
for example1 we see  cones entirely     

built up of pumice4 ,such pumice-cones  
resemble in  the angle of their slope   
7see fig4 #da1 facing p4 #abd71 the     
ordinary  scoria-cones1 but are of a    
brilliant white colour1 appearing as if 
covered with snow4    ,sidenote3        
,,preservation ,,of ,,scoria-,,cones4   
,ordinary scori are usually of a black  
colour when first ejected1 but  after a 
short time the black oxide of iron      
7magnetite7 which they  contain1        
attracts the oxygen of the air and      
moisture1 and assumes the  reddish-brown
 colour of iron-rust4 ,under such       
circumstances the heaps  of black       
material gradually acquire the red-brown
 colour which is  characteristic of so  
many of the scoria-cones around ,etna1  
and in the  ,auvergne and the ,eifel4   
,the moisture of the air1 and the rain  
falling  upon these loose cindery heaps1
 cause them to decompose upon their     
surfaces2 the action is facilitated by  
the growth of the lower forms  of       
vegetation1 such as mosses and lichens1 

and thus at last a soil is  produced on 
the surfaces of these conical piles of  
loose materials  which may support an   
abundant vegetation4 ,cinder- or        
scoria-cones are  not uncommonly found  
retaining in a most perfect manner their
 regular1  conical form1 the lips of    
their craters being sharp and unbroken  
as if  the cone were formed but         
yesterday1 while their slopes may       
nevertheless  be covered with a rich    
soil supporting abundant grass and      
forest-trees4  ,it may at first sight   
seem difficult to understand how a loose
 mass of  scori could have so long      
withstood the action of the rain and    
floods1  retaining so perfectly its even
 slopes and sharp ridges4 ,a little     
consideration will1 however1 convince us
 that it is the very loose and  pervious
 nature of the materials of which       
scoria-cones are composed1  which tends 
to their perfect preservation4 ,the rain
 at once sinks into  their mass1 before 
it has time to form rivulets and streams

 which would  wear away their surfaces  
and destroy the regularity of their     
outlines4    ,scoria- and pumice-cones  
are frequently found to be acted upon by
 acid  vapours to such an extent that   
the whole of the materials is reduced   
to a white pulverulent mass4 ,in these  
cases the oxides of iron and the        
alkalis have united with the sulphuric  
or hydrochloric or carbonic  acids1 the 
compounds being carried away in solution
 by the rain-water  falling on the mass2
 the materials left are silica1 the     
hydrated  silicate of alumina1 and      
hydrated sulphate of lime 7gypsum71 all 
of  which are of a white colour4        
,cinder- or scoria-cones1 and           
pumice-cones1 are often found raised  by
 the action of winds to a greater       
elevation on one side than the  other1  
in the manner already described4 ,one   
side of the cone is often  seen to be   
more or less completely swept away by an
 outwelling stream  of lava1 and thus   
breached cones are formed 7see fig4 #dj1

 p4 #abc74  ,not unfrequently we find a 
number of cones which are united more or
  less completely at their bases1 as in 
,vulcanello 7fig4 #f1 p4 #dc71 the      
several vents being so near together    
that their ejections have mingled  with 
one another4 ,cones composed entirely of
 fragmentary materials  often show an   
approach to the beautifully curved      
slopes which we have  described as being
 so characteristic of volcanoes1 as may 
be seen in  fig4 #da1 facing p4 #abd4   
,in the case of scoria- and pumice-cones
 this  curvature is probably due to the 
rolling downnwards and outwards of the  
larger fragments4    ,we have already   
pointed out that with the scori there   
are often  ejected fragments torn from  
the sides of the volcanic vents4        
,sometimes  such fragments are so       
numerous as to make up a considerable   
portion of  the mass of the volcanic    
cones4 ,thus in the ,eifel we find      
hills1 of  by no means insignificant    
size1 completely built up of small scori

  and broken fragments of slate torn    
from the rocks through which the        
volcanic fissures have been opened4     
,occasionally we see that few or no     
scori have been ejected1 and the        
volcanic vents are surrounded simply  by
 heaps of burnt slate4    ,the smaller  
fragmentary materials ejected from      
volcanic vents--such  as lapilli and    
dust--rest in heaps1 having a different 
angle of slope  from those formed by    
scori4 ,in many cases1 as we have seen1 
such  finely-divided materials descend  
in the condition of mud1 which flows    
evenly over the surface of the growing  
cone and consolidates in beds of  very  
regularly stratified 'tufa' or 'tuff4'  
,sidenote3 ,,characters ,,of            
,,tuff-,,cones4    ,the 'tuff-cones'    
thus formed differ in many important    
respects from the  scoria-cones already 
described4 ,the slope of their sides    
varies from  #ae to #cj1 and is almost  
always considerably less than in scoria-
 and  pumice-cones4 ,the tuff-cones     

undergo much more rapid degradation from
  rain and moisture than do the         
scoria-cones2 for1 though the materials 
of the former 'set1' as we have seen1   
into a substance of considerable        
hardness1 yet this substance1 being much
 less pervious to water than  the loose 
scoria heaps1 permits of the formation  
of surface-streams  which furrow and    
wear away the sides of the cones4       
,sometimes the sides  of the crater are 
found to be almost wholly removed by    
atmospheric  denudation1 and only a     
shallow depression is found occupying   
the  site of the crater2 such a case is 
represented in fig4 #ei4 ,we not        
unfrequently find the whole slopes of   
such cones to be traversed by a  series 
of radiating grooves passing from the   
summit to the base of the  mountains1   
these channels being formed by water1   
which has collected  into streams1      
flowing down the slopes of the          
mountains4 ,the volcanic  cone1 under   
these circumstances1 frequently presents

 the appearance of  a partially opened  
umbrella4 ,owing to the impervious      
character of the  materials composing   
tuff-cones1 their craters are frequently
 found to  be occupied by lakes4        
,illustration3 ,fig4 #ei4--,summit of   
the volcano of ,monte ,sant' ,angelo in 
,lipari exhibiting a crater with walls  
worn down by denudatioh4    ,tufas have 
usually a white or yellowish-brown      
colour1 and these are the  colours      
exhibited by the cones composed of this 
material before they  become covered by 
vegetation4 ,tufas scori1 and lavas     
usually crumble  down to form a very    
rich soil1 and many of the choicest     
wines are  produced from grapes grown on
 the fertile slopes of volcanic         
mountains4  ,when1 however1 as not      
unfrequently happens1 the materials are 
finely  divided and incoherent1 they are
 so easily driven about by the winds    
that cultivation of any kind is rendered
 almost impossible4 ,in the  ,islands of
 ,stromboli and ,vulcano the gardens    

have to be surrounded by  high fences to
 prevent them from being overwhelmed by 
the ever-shifting  masses of volcanic   
sand4    ,sidenote3 ,,characters ,,of   
,,lava-,,cones4    ,there are some cones
 which are composed in part of scori and
 in part  of tufa4 ,hence we are        
sometimes at a loss whether to group    
them with  the one class of cones or the
 other4 ,but in the majority of cases1  
scoria- and tuff-cones present the      
sufficiently well-marked and            
distinctive characters which we have    
described4    ,lava-cones differ quite  
as greatly in their forms as do the     
cones  composed of fragmentary          
materials1 the variations being         
principally  determined by the degree of
 liquidity of the lavas4    ,we         
sometimes find that outwelling masses of
 lava1 when issuing in small  quantities
 from a vent1 accumulate in             
cauliflower-shaped masses1 or  sometimes
 in the form of a column1 or bottle4    
,professor ,j4 ,d4 ,dana  describes many

 such fantastically-formed masses of    
lava as being found  in ,hawaii1 one of 
which is represented in fig4 #be 7p4    
#ajj74    ,when the lava issues from the
 vent in great quantities it tends to   
flow on all sides of it1 and to build up
 a great conical heap above  the        
orifice4 ,if the lava be very liquid it 
flows to great distances1  resting at a 
very slight slope4 ,thus we find that   
the volcanoes of  ,hawaii have been     
built up of successive ejections of very
 liquid lava1  which have formed cones  
having a slope of only #f to #h1 but of 
such  enormous dimensions that the      
diameter of their bases is seventy miles
  and their height #ad1jjj feet4        
,illustration3 ,fig4 #fj4--,outlines of 
,lava-cones4    #a4 ,mauna ,loa1 in     
,hawaii4 ,composed of very fluid lava4  
#c4 ,the  ,schlossberg of ,teplitz1     
,bohemia4 ,composed of very imperfectly 
fluid or  viscid lava4    ,if1 on the   
other hand1 the lava be viscid1 or very 
imperfectly liquid  in character1 it    

tends to accumulate immediately around  
the vent2 fresh  ejections force the    
first extruded matter outwards1 in the  
manner so  well illustrated by ,dr4     
,reyer's experiments1 and at last a more
 or less  steep-sided bulbous mass is   
formed over the vent4 ,such bulbous     
masses1  composed of imperfectly fluid  
lavas1 occur in many volcanic districts1
  and constitute hills of considerable  
size4 ,from the tendency of matters     
thus extruded to choke up the vents1    
however1 these volcanoes composed  of   
viscid lavas cannot be expected to      
attain the vast dimensions  reached by  
some of those composed of very liquid   
lavas4 ,the difference  in the forms of 
lava-cones composed of very fluid or of 
somewhat  viscid materials is           
illustrated in fig4 #eh4 ,when the      
interior of such  steep-sided volcanic  
mountains composed of viscid materials  
is exposed  by the action of denuding   
forces1 the peculiar internal structure 
we  have described is displayed by them4

 ,in the ,chodi-,berg of ,hungary1  a   
great bulbous mass of andesitic rock1   
this endogenous structure is  admirably 
displayed4 ,it is also well seen in the 
excavation of the hill  of the ,grand   
,sarcoui1 a similar mass1 composed of   
altered trachyte1  which has been       
erupted in the midst of a scoria-cone in
 the ,auvergne4  ,see fig4 #dd 7p4      
#abf74    ,sidenote3 ,,characters ,,of  
,,composite ,,cones4    ,most of the    
great volcanic mountains of the globe   
belong to the  class of 'composite      
cones1' and are built up by alternate   
ejections  of fluid lava and fragmentary
 materials4 ,the slope of the sides in  
such composite cones is subject to a    
wide range of variation1 being          
determined in part by the degree of     
liquidity of the lavas1 in part  by the 
nature of the fragmentary materials     
ejected1 and in part by  the proportions
 which the fragmentary and              
lava-ejections bear to one  another4    
,but there is another set of causes     

which tends to modify the form  and     
character of these composite1 volcanic  
cones4 ,as we have already  pointed out1
 the sides of such cones are liable to  
be rent asunder from  time to time1 and 
the fissures so produced are injected   
with masses of  liquid lava from below4 
,these fissures1 rent in the sides of   
volcanic  cones1 often reach the surface
 and eruptive action takes place1 giving
  rise to the formation of a cone1 or   
series of cones1 upon the line  of the  
fissure 7fig4 #fa74 ,such small cones   
thrown up on the flanks  of a great     
volcanic mountain are known as          
'parasitic cones'2 though  subordinate  
to the great mountain mass1 they may be 
in themselves of  considerable          
dimensions4 ,among the hundreds of      
parasitic cones which  stud the flanks  
of ,etna1 there are some which are      
nearly #hjj feet in  height4            
,illustration3 ,fig4 #fa4--;,diagram    
illustrating the formation of           
,parasitic ,cones along lines of fissure

 formed on the flanks of a great        
volcanic mountain4    ,illustration3    
,fig4 #fb4--,outline of ,etna1 as seen  
from ,catania4    ,sidenote3 ,,formation
 ,,of ,,parasitic ,,cones4    ,the      
building up of parasitic cones upon the 
flanks of a volcanic  mountain tends1 of
 course1 to destroy its regular conical 
form4 ,this  may be well seen in ,etna1 
which1 by the accumulation of materials 
upon its flanks1 has become a remarkably
 'round-shouldered' mountain4  7,see    
figs4 #fb and #fc47 ,at the same time it
 must be remembered that  materials     
erupted from the central vent tend to   
fill up the hollows  between these      
parasitic cones1 and thus to restore to 
the mountain its  regularly conical     
form4    ,illustration3 ,fig4           
#fc4--,outline of ,etna1 as seen from   
the ,val del  ,bronte4    ,illustration3
 ,fig4 #fd4--,plan of the ,volcano      
forming the ,island of  ,ischia4      a1
 a1 a4 ,the semi-circular crater-ring of
 ,epomeo4    b1 c1 d4 ,lava-currents    

which have flowed from the principal    
crater4    e1 f1 g1 h4 ,plateaux formed 
by ancient lava-currents4    k4         
,montagnone4        l4 ,monte ,rotaro4  
m4 ,monte ,tabor4    ,parasitic cones   
and craters on the slopes    n4         
,castiglione4      of the mountain4     
o4 ,lago di ,bagno4     p4 ,the         
,cremate4       r4 ,lava-stream of the  
,arso1 which flowed from the ,cremate in
 #acja4    x1 x1 x4 ,raised beaches on  
the shores of the island1 showing that  
it       has recently undergone         
elevation4      ,the ,island of ,ischia 
is a good example of a great volcanic   
cone the  flanks of which are covered   
with numerous small parasitic cones4    
,while  the great central volcano has   
evidently been long extinct1 and one    
side of its crater-wall is completely   
broken down1 some of the small          
parasitic cones around its base have    
been formed within the historical       
period--one of them as recently as the  
year #acjb4 ,fig4 #fd is a plan of  the 

,island of ,ischia1 showing the numerous
 parasitic cones scattered  over the    
slopes of the principal cone4           
,illustration3 ,fig1 #fe4--;,a primary  
,parasitic ,cone with a secondary one   
at its base--,ischia4    a4 ,monte      
,rotaro4 b4 ,monte ,tabor4 c4           
,lava-stream flowing from the  latter4  
,in one case we find that a parasitic   
cone1 the ,monte ,rotaro1 has itself  a 
similar smaller cone1 which is parasitic
 to it1 at its foot2 this  secondary    
parasitic cone gives off a small        
lava-stream of trachyte1  which has     
flowed down to the sea4 7,see fig4 #fe47
    ,illustration3 ,fig4                
#ff4--,scoria-cone near ,auckland1 ,new 
,zealand1 with a  lava-current flowing  
from it4    ,the strata beneath the     
volcanic cone are exposed in the        
sea-cliff1 and  exhibit proofs of       
depression having taken place4          
,illustration3 ,fig4 #fg4--,section of  
rocks below the ancient triassic        
volcano of ,predazzo in the ,tyrol4     

,the position of the strata a b c1 etc41
 indicates a central  subsidence4       
,sidenote3 ,,subsidence ,,beneath       
,,volcanic ,,vents4    ,most great      
volcanic mountains exhibit a tendency   
towards a subsidence  of their central  
portions1 which may take place either   
during or  subsequently to their period 
of activity4 ,when we examine the strata
  upon which a volcano has been built   
up1 but which are now exposed to  our   
study by denuding forces1 we usually    
find that they incline towards  the     
centre of the eruptive activity4 7,see  
figs4 #ff and #fg47 ,two causes  may    
contribute to bring about this result4  
,in the first instance1  we must remark 
that the piling up of materials around  
the volcanic  vent causes the subjacent 
strata to be subjected to a degree of   
pressure far is excess of that which    
acts upon the surrounding rocks4  ,and  
secondly1 it must be borne in mind that 
the continual removal  of material from 
below the mountain must tend to the     

production of  hollows1 into which the  
overlying strata will sink4 ,the effect 
of this  central subsidence is to give  
to the flanks of volcanic cones those   
beautifully curved outlines which       
constitute so striking a feature in     
,vesuvius 7see fig4 #ag1 p4 #hg71       
,fusiyama 7see fig4 #gg1 ,no4 #a1 facing
 p4  #agh71 and many other volcanic     
mountains4    ,there seems1 at first    
sight1 to be scarcely any limit to the  
dimensions  which these great composite 
volcanic cones may attain3 the lateral  
eruptions tending to enlarge the area of
 the base of the mountain1  and1 by the 
injection of the fissures1 to knit      
together and strengthen  its structure1 
while the central eruptions continually 
increase the  elevation of the mass4    
,great1 however1 as is the force which  
is  concerned in the production of our  
terrestrial volcanoes1 it has its       
limits2 and1 at last1 the piling up of  
materials will have gone on  to such an 
extent1 that the active forces beneath  

the volcano are no  longer competent    
either to raise materials to the        
elevated summit of  the mountain or to  
tear asunder its strengthened and       
fortified flanks4  ,under these         
circumstances1 the volcanic forces1 if  
they have not  already exhausted        
themselves1 will be compelled to find   
weak places in  the district surrounding
 the volcano1 at which fissures may be  
produced  and the phenomena of eruption 
displayed4    ,sidenote3 ,,shifting ,,of
 ,,volcanic ,,foci4    ,some volcanic   
cones exhibit evidence that during the  
series of  eruptions by which they have 
gradually been built up1 the centre of  
volcanic action has shifted to another  
point within the mountain4 ,thus  ,lyell
 has shown1 in the case of ,etna1 that  
during the earlier periods  in the      
history of the mountain the piling up of
 materials went on  around a centre     
which is now situated at a distance of  
nearly four  miles from the present     
focus of eruptive activity4 ,some of our

 old  ,british volcanoes1 of which the  
denuded wrecks exist in the ,western    
,isles of ,scotland1 show similar       
evidence of a shifting of the axis of   
eruption4    ,one of the most           
conspicuous features of a volcanic cone 
is the great  depression or crater found
 at its summit4 ,in describing the      
internal  structure of volcanic cones1  
we have seen how these craters are      
produced and acquire their inverted     
conical form1 by the slipping and       
rolling back of materials towards the   
centre of eruptive action4    ,almost   
all volcanic cones exhibit craters1 but 
in those which are  formed entirely by  
the outwelling of viscid lavas the      
central  depression is often slight and 
inconspicuous1 and occasionally         
altogether wanting4 ,it frequently      
happens1 however1 that eruptive  action 
has ceased at the centre of a volcano1  
and its summit-crater  may by denudation
 be entirely destroyed1 while new and   
active craters  are formed upon its     

flanks4 ,stromboli furnishes us with an 
admirable  example of this kind 7see    
fig4 #a1 facing p4 #aj74 ,other         
volcanoes may  exhibit several craters1 
one at the summit of the mountain and   
others  upon its flanks4 ,of this we    
find a good example in ,vulcano 7fig4   
#f1 p4  #dc74    ,illustration3 ,fig4   
#fh4--;,cotopaxi 7#ai1fjj feet71 as seen
 from a  distance of ninety miles4      
,when a volcano has been built up by    
regular and continuous eruptions  from  
the same volcanic vent1 the size of the 
crater remains the same1  while the     
volcano continually grows in height and 
in the diameter of  its base4 ,the size 
of the crater will be determined by the 
eruptive  force at the volcanic centre1 
the size of the mountain by the duration
  of the volcanic activity and the      
quantity of material ejected4 ,in the   
earliest stage of its history1 such a   
volcano will resemble ,monte  ,nuovo1   
which has a crater reaching down almost 
to the base of the  mountain2 in the    

later stages of its history1 such a     
volcano will  resemble ,cotopaxi 7fig4  
#fh7 and ,citlaltepetl 7fig4 #fi71 in   
which the  crater1 though of far greater
 absolute dimensions than that of ,monte
  ,nuovo1 bears but a small proportion  
to the vast cone at the summit of  which
 it is situated4    ,illustration3 ,fig4
 #fi4--;,citlaltepetl1 or the ,pic      
d',orizaba1 in ,mexico  7#ag1cgj feet71 
as seem from the forest of ,xalapa4     
,sidenote3 ,,origin ,,of ,,volcanic     
,,craters4    ,in the great majority of 
volcanoes1 however1 eruptive action does
 not  go on by any means regularly and  
continuously1 but terrible paroxysmal   
outbursts occur1 which suddenly enlarge 
the dimensions of the crater to  an     
enormous extent4    ,in the year #aggb1 
there occurred a volcanic eruption in   
the ,island  of ,java1 which is perhaps 
the most violent and terrible that has  
happened within the historical period4  
,a lofty volcanic cone1 called          
,papandayang1 #i1jjj feet high1 burst   

into eruption1 and1 in a single  night1 
#cj1jjj1jjj1jjj cubic feet of materials 
were thrown into the  atmosphere1       
falling upon the country around the     
mountain where no less  than forty      
villages were buried4 ,after the        
eruption1 the volcano was  found to have
 been reduced in height from #i1jjj to  
#e1jjj feet1 and  to present a vast     
crater in its midst1 which had been     
formed by the  ejection of the enormous 
mass of materials4    ,many similar     
cases might be cited of the removal of a
 great part of a  mountain-mass by a    
sudden1 paroxysmal outburst4 ,in some   
cases1 indeed1  the whole mass of a     
mountain has been blown away during a   
terrific  eruption1 and the site of the 
mountain is now occupied by a lake4     
,this  is said to have been the case    
with the ,island of ,timor1 where an    
active  volcano1 which was visible from 
a distance of #cjj miles at sea1 has    
entirely disappeared4    ,the removal of
 the central portion of great volcanic  

mountains by  explosive action1 gives   
rise to the formation of those vast1    
circular1  crater-rings of which such   
remarkable examples occur in many       
volcanic  districts4 ,these crater-rings
 present a wall with an outer slope     
agreeing with that of the volcanic cone 
of which they originally formed  a part1
 but with steep inner cliffs1 which     
exhibit good sections of the  beds of   
tuff1 ash1 and lava with the            
intersecting dykes of which the         
original volcano was built up4 ,near    
,naples1 one of these crater-rings1     
with sloping outer sides and steep inner
 ones1 is employed to form the  royal   
game-preserve of ,astroni1 the only     
entrance to the crater being  closed by 
gates4    ,sidenote3 ,,formation ,,of   
,,crater-,,lakes4    ,as these          
crater-rings are usually composed of    
materials more or  less impervious to   
water1 they often become the site of    
lakes4 ,the  beautiful circular lake of 
,laach1 in the ,rhine ,provinces1 with  

the  numerous similar examples of       
,central ,italy--,albano1 ,nemi1        
,bracciano1  and ,bolsena--the lakes of 
the ,campi ,phlegri 7,agnano1 ,avernus1 
c471  and some similar lakes in the     
,auvergne1 may be adduced as examples of
  crater-rings which have become the    
site of lakes4    ,illustration3 ,fig4  
#gj4--,lac ,paven1 in the ,auvergne4    
a4 ,scori4 b4 ,basalt4    ,one of the   
most beautiful of the crater-lakes in   
the ,auvergne is  ,lac ,paven 7fig4     
#gj71 which lies at the foot of a       
scoria-cone1 ,mont  ,chalme1 and is     
itself surrounded by masses of ejected  
materials4 ,the  crater-lake of ,bagno1 
in ,ischia 7fig4 #ga71 has had a channel
 cut  between it and the sea1 so that it
 serves as a natural harbour4 ,the  lake
 of ,gustavila1 in ,mexico 7fig4 #gb71  
is an example of a crater-lake  on a    
much larger scale4    ,in many of these 
crater-rings the diameter of the        
circular space  enclosed by them is     
often very great indeed as compared with

 the height  of the walls4              
,illustration3 ,fig4 #ga4--,the         
crater-lake called ,lago del ,bagno1 in 
,ischia1 converted into a harbour4      
,illustration3 ,fig4 #gb4--,lake of     
,gustavila1 in ,mexico4    7,the        
terraces round the lake have been       
artificially formed47    ,sidenote3     
,,dimensions ,,of ,,crater-,,lakes4     
,two of the largest crater-rings in the 
world are found in ,central  ,italy1 and
 are both occupied by lakes1 the        
circular forms of which  must strike    
every observer4 ,the ,lago di           
,bracciano1 which lies to  the          
north-west of ,rome1 is a circular lake 
six and a half miles in  diameter1      
surrounded by hills which at their      
highest point rise to the  height of    
#a1dhf feet above the sea1 while the    
surface of the waters  of the lake is   
#fdj feet above the sea-level4 ,the     
,lago di ,bolsena is  somewhat less     
perfectly circular in outline than the  
,lago di ,bracciano2  it has a length   

from north to south of ten-and-a-quarter
 miles and a  breadth from east to west 
of nine miles2 the surface of the waters
 of  this lake is #ifb feet above that  
of the waters of the ,mediterranean4    
,the lake of ,bolsena1 like that of     
,bracciano1 is surrounded by hills      
composed of volcanic materials2 the     
highest points of this ring of  hills   
rise to elevations of #fhd1 #ghj1 and   
#ihe feet respectively above  the waters
 of the lake4    ,in these great        
circular lakes of ,bolsena and          
,bracciano1 as well as in  the smaller  
ones of ,albano1 ,nemi1 and the lakes of
 ,frascati in the same  district1 the   
vast circular spaces enclosed by them1  
the gradual outer  slope of the ring1   
and the inner precipices which bound the
 lake1 all  afford evidence of the      
explosive action to which they owe their
 origin4    ,but while the vast         
crater-rings we have mentioned are      
frequently found  to be occupied by     
lakes1 there are many other similar     

crater-rings  which remain dry1 either  
from the materials of which they are    
composed  being of more pervious        
character1 or from rivers having cut a  
channel  through the walls of the       
crater1 in this way draining off its    
waters4    ,thus in the ,campi ,phlegri1
 while we have the craters of ,agnano   
and  ,avernus forming complete circular 
lakes1 ,astroni has only a few          
insignificant lakelets on its floor1 and
 the ,pianura1 the ,piano di  ,quarto1  
which have each a diameter of three or  
four miles1 with many  others1 remain   
perfectly dry4 ,in the vicinity of the  
great crater-lakes  of ,central ,italy  
we find the crater-ring of the          
,vallariccia1 which has  evidently once 
been a lake but is now drained1 its     
floor being covered  with villages and  
vineyards4    ,sidenote3                
,,crater-,,rings ,,surrounding ,,cones4 
,a comparison of these vast crater-rings
 leads us to the conclusion that  in the
 majority of cases1 if not in every     

instance1 they are composed  almost     
entirely of volcanic tuff and dust4 ,in 
the case of the more  solidly-built     
composite volcanic cones1 the volcanic  
forces1 as we have  seen1 produce       
fissures in the mass1 and along these   
fissures parasitic  cones are thrown up1
 the tension of the mass of imprisoned  
vapours  below the mountain being thus  
from time to time relieved4 ,but in the 
case of a volcanic cone composed of     
loose fragmentary materials1 such       
temporary relief is impossible4 ,the    
cracks1 as soon as they originate1  will
 be filled up and choked by the falling 
in of materials from above  and at their
 sides4 ,in this way the eruptive action
 will be continually  repressed1 till at
 last the imprisoned vapours acquire    
such a high  state of tension that the  
outburst1 when it occurs1 is of the most
  terrible character1 and the whole     
central mass of the volcano is blown    
into the air4 ,it may often seem        
surprising that the ejection of such    

vast masses of material from the centre 
of a volcanic cone does not  effect more
 in the way of raising the height of the
 crater-walls4 ,but  it must be         
remembered that1 in the case of craters 
of such vast area1  the majority of the 
ejected materials must fall back again  
within  its circumference4 ,by repeated 
ejections these materials will at last  
be reduced to such an extreme state of  
comminution that they can be  borne away
 by the winds1 and spread over the      
country to the distance of  hundreds or 
thousands of miles4 ,after great        
volcanic outbursts enormous  areas are  
thus found covered with fine volcanic   
dust to the depth of  many inches or    
feet4    ,illustration3 ,fig4           
#gc4--,peak of ,teneriffe in the ,canary
 ,islands  7#ab1ahb ft471 surrounded by 
great crater-rings4    ,sometimes1 as in
 the case of the ,lago di ,bracciano1   
the eruptive forces  appear to have     
entirely exhausted themselves in the    
prodigious outburst  by which the great 

crater was produced4 ,but in other      
cases1 as in that  of the ,lago di      
,bolsena1 the eruptive action was       
resumed at a later  date1 and small     
tuff-cones were thrown up upon the floor
 of the crater2  these now rise as      
islands above the surface of the lake4  
,in other  cases1 again1 the eruptive   
action was resumed after the formation  
of  the great crater-ring1 with such    
effect that bulky volcanic cones were   
built up in the midst of the crater-ring
 which surrounds them like a  vast wall2
 examples of this are exhibited in the  
extinct volcanoes of  ,rocca ,monfina   
and ,monte ,albano4 ,some of the        
grandest volcanoes of the  globe1 such  
as ,teneriffe 7fig4 #gc71 the volcanoes 
of ,mauritius and  ,bourbon 7figs4 #gd  
and #ge71 and many others that might be 
cited1 are  thus found to be surrounded 
by vast crater-rings4 ,vesuvius itself  
is  surrounded by the crater-ring of    
,somma 7fig4 #gf74    ,illustration3    
,fig4 #gd4--,the volcano of ,bourbon1   

rising in the midst of  a crater-ring   
four miles in diameter4                 
,illustration3 ,fig4 #ge4--,the volcano 
of ,bourbon1 as seen from another  point
 of view1 with three concentric         
crater-rings encircling its base4       
,sidenote3 ,,basaltic ,,cones ,,in      
,,trachytic ,,crater-,,rings4    ,this  
formation of cone within crater1 often  
many times repeated1 is  very           
characteristic of volcanoes4 ,the       
craters mark sudden and violent         
paroxysmal outbursts1 the cones are the 
result of more moderate but             
long-continued ejection4 ,sometimes1 as 
at ,vesuvius in #agfg 7fig4 #ae1  p4    
#he71 we find a nest of craters and     
cones which very strikingly  exemplifies
 this kind of action4    ,illustration3 
,fig4 #gf4--,vesuvius1 as seen from     
,sorrento1 half  encircled by the       
crater-ring of ,somma4    ,we shall     
point out1 hereafter1 that at most      
volcanic centres the  ejection of       
trachytic lavas precedes that of the    

basaltic lavas4 ,now it  is these       
trachytic lavas which principally give  
rise to the formation  of the light     
lapilli of which tuff-cones are formed4 
,hence it is that  we so frequently     
find1 as in the case of ,vesuvius1      
,rocca-,monfina1 and  many other        
volcanoes1 that a great crater-ring1    
largely composed of  tuffs1 encloses a  
cone built up of more basic lavas4      
,in fig4 #gg we have shown by a series  
of outline sections the various  forms  
assumed by volcanoes in consequence of  
the different kinds of  eruptive action 
going on in them3--    #a4 ,is an       
outline of ,fusiyama1 an almost perfect 
cone1 with a small  crater at its       
summit4 ,the sides of this volcano      
admirably illustrate  the beautiful     
double curves characteristic of volcanic
 cones4    #b4 ,hverfjall in ,iceland1 a
 volcanic cone with a large crater1     
reaching  almost to its base4    #c4    
,the crater-lake of ,bracciano1 in which
 the area of the crater is out  of all  

proportion to the height of the         
crater-walls4    #d4 ,rocca-,monfina1 in
 ,southern ,italy1 a tuff-cone of large 
dimensions1  in the midst of which an   
andesitic lava-cone has been built up4  
#e4 ,teneriffe1 in the ,canary ,islands1
 in which a perfect volcanic cone  has  
been built up in the centre of an       
encircling crater-ring4    #f4 ,vulcano1
 in the ,lipari ,islands1 in which1 by  
the shifting of the  centre of volcanic 
activity along a line of fissure1 a     
series of  overlapping volcanic cones   
has been produced4    ,illustration3    
,fig4 #gg4--,outlines of various        
,volcanoes1 illustrating  the different 
relations of the craters to cones4      
,sidenote3 ,,submarine ,,volcanoes4     
,while speaking of the varieties of form
 assumed by volcanic cones and  craters1
 we must not forget to notice the       
effects which are produced  by denuding 
forces upon them4 ,in the case of       
submarine volcanoes1 like  the          
celebrated island called by the ,english

 ,graham ,isle1 by the ,french  ,isle   
,julie1 and by the ,germans the ,insel  
,ferdinandez 7fig4 #gh71 which  was     
thrown up off the coast of ,sicily in   
#ahca1 it was evident that  volcanic    
outbursts taking place at some depth    
below the level of the  sea gradually   
piled up a cone of scori with a crater  
in its midst4  ,by constant accessions  
to its mass1 this scoria-cone was       
eventually  raised above the sea-level1 
but the action of the waves upon the    
loose  materials soon destroyed the     
crater-walls and eventually reduced the 
island to a shoal4 ,it is evident that  
in all cases in which eruptions  take   
place beneath the sea-level1 and the    
loose materials are exposed  during     
their accumulation to the beating of the
 sea-waves1 the form  of the volcanic   
cone so produced will be greatly        
modified by the  interaction of the two 
sets of opposed causes1 the eruptive    
forces from  below and the distributive 
action of the sea-waves4                

,illustration3 ,fig4 #gh4--;,island     
thrown up in the ,mediterranean ,sea in 
,july and ,august #ahha4    7,the view  
was taken in the month of ,september1   
after the sides of the  crater had been 
washed away by the waves47    ,craters  
when once formed are often rent across1 
along the line of the  fissure above    
which they are thrown up4 ,thus the     
crater of ,vesuvius was  in #ahgb rent  
completely asunder on one side1 so that 
it was possible  to climb through the   
fissure thus produced and reach the     
bottom of the  crater4 ,streams flowing 
down the sides of the crater1 and       
escaping  through such a rent1 may in   
the end greatly modify the form and     
disguise the characters of a volcanic   
crater4 ,of this kind of action we  have
 a striking example in the ,val del     
,bove of ,etna4    ,volcanoes1 as we    
shall point out in the sequel1 are after
 their  extinction frequently submerged 
beneath the waters of the ocean4 ,the   
sea entering the craters1 eats back     

their cliff-like sides and enlarges     
their areas4 ,such denuded waters are   
called 'calderas1' the channels  into   
them 'barrancos4'    ,sometimes the     
action of the waves upon a partially    
submerged volcano  has led to the       
cutting back of its slopes into steep   
cliffs1 at the  same time that the      
crater-ring is enlarged4 ,in such cases 
we have left  a more or less complete   
rocky ring1 composed of alternating     
lavas and  fragmentary materials4 ,of   
such a ruined crater-ring1 the ,island  
of ,st4  ,paul in the ,south ,atlantic  
affords an admirable example4    ,when  
the action of denudation has gone still 
further1 all the lavas and  tuffs       
composing the cone may be completely    
removed and nothing left but  masses of 
the hard and highly-crystalline rocks   
which have cooled down  slowly in the   
heart of the volcano4 ,an example of    
this kind is afforded  to us by ,st4    
,kilda1 the remotest member of the      
,british ,archipelago4    ,but although 

the majority of volcanic craters are    
clearly formed by  explosive action1    
there are some craters1 like those of   
,kilauea in  ,hawaii1 which probably owe
 their origin to quite a different set  
of  causes4 ,in this case the explosive 
action at the vent is but slight1  and  
the crater1 which is of very irregular  
form1 appears to have  originated in a  
fissure1 which has been slowly enlarged 
by the liquid  lavas encroaching upon   
and eating away its sides4 ,such craters
 as  these1 however1 appear to be       
comparatively rare4    ,besides the     
great volcanic mountains composed of    
lava1 scori1 tuff and  ash1 there are   
other structures which are formed around
 volcanic vents  even when these do not 
eject molten rock-masses4 ,the water    
which issues  in these cases either as  
steam or in a more or less highly heated
  condition frequently carries materials
 in suspension or solution1 and  these  
sometimes accumulate in considerable    
quantities around the vent4             

,sidenote3 ,,formation ,,of             
,,mud-,,volcanoes4    ,when fissures are
 formed in the midst of loose           
argillaceous materials1  such as are    
frequently produced by the decomposition
 of volcanic rocks1  the waters which   
issue through them are sometimes so     
charged with muddy  matter that this    
accumulates to form cones having all the
 general  characters of volcanic        
mountains1 and which occasionally rise  
to the  height of #bej feet4 ,the gases 
and vapours which issue from these      
'mud-volcanoes' are those which are     
known to be emitted from volcanic  vents
 at which the action going on is not    
very intense4 ,daubeny and  others have 
suggested that these mud-volcanoes may  
be the result of  actions which have    
little or no analogy with those which   
take place  at ordinary volcanic vents1 
and that the combustion of subterranean 
beds of sulphur and similar causes would
 be quite competent to their            
production4 ,but inasmuch as these      

mud-volcanoes are almost always         
situated in regions in which the more   
powerful volcanic action has  only      
recently died away1 and the gases and   
vapours emitted by them are  very       
similar in character to those which     
issue from volcanoes1 there  does not   
appear to be any good reason for        
doubting that they should be  classed as
 truly volcanic phenomena4              
,mud-volcanoes are found in ,northern   
,italy near ,modena1 in ,sicily near    
,girgenti1 on the shores of the ,sea of 
,azof and the ,caspian1 in ,central     
,america1 and in other parts of the     
globe4 ,the gas frequently escapes  from
 them with such violence that mud is    
thrown into the air to the  height of   
several hundreds of feet4 ,sometimes    
this gas is inflammable1  consisting of 
sulphuretted hydrogen1 hydrogen1 or some
 hydrocarbons1  and these gases         
occasionally take fire1 so that true    
flames issue from  these mud-volcanoes4 
,in other cases the mud-volcanoes appear

 to be  formed by either hot or cold    
springs containing large quantities of  
suspended materials1 and the liquid mud 
issues from the vent without  any       
violent eruptive action4                
,illustration3 ,fig4 #gi4--,sinter-cones
 surrounding the orifices of  ,geysers4 
#a4 ,basin of the ,great ,geyser1       
,iceland4 #b4 ,hot spring cone4 #c4 ,old
  ,faithful4 #d4 ,the ,great ,geyser4   
#e4 ,liberty ,cap4 7#b1 #c1 #d and #e   
are in  the ,yellowstone ,park district 
of the ,rocky ,mountains47    ,sidenote3
 ,,formation ,,of ,,sinter-,,cones4     
,the soluble materials which waters     
issuing from volcanic vents deposit  on 
their sides are chiefly silica and      
carbonate of lime4    ,hot springs1     
whether intermittent or constant1 often 
contain large  quantities of silica in  
solution4 ,the solution of this silica  
is  effected1 at the moment of its      
separation from combination with the    
alkali or alkaline earths1 during the   
decomposition of volcanic rocks1  and is

 favoured by the presence of alkaline   
carbonates in the water1  and the high  
temperature and the pressure under which
 it exists in the  subterranean regions4
 ,when the water reaches the surface    
and1 being  relieved from pressure1     
begins to cool down the silica is       
deposited4  ,by this deposited silica   
the basins around the geysers of        
,iceland are  formed4 ,sometimes conical
 structures are built up around the     
vents of  hot springs by the deposition 
of silica from their waters4 ,examples  
of this kind abound in the ,national    
,park of ,colorado1 where they have     
received fanciful names1 such as the    
,beehive1 ,liberty ,gap1 c4 ,this       
deposited silica is known to geologists 
as sinter4 ,the forms of some of  the   
structures which surround the orifices  
of geysers is shown in fig4  #gi4 ,the  
',liberty ,cap' is an extinct           
geyser-cone fifty feet high and  twenty 
feet in diameter4    ,hot and cold      
springs rising in volcanic regions are  

often highly  charged with carbonic     
acid1 and in passing through calcareous 
rocks  dissolve large quantities of     
carbonate of lime4 ,upon exposure to the
  atmosphere1 the free carbonic acid    
escapes and the carbonate of lime  is   
deposited in the form known as          
'travertine4' ,such springs occur  in   
great numbers in many volcanic regions4 
,in the ,auvergne great  rock-masses    
occur formed of carbonate of lime       
deposited from a state  of solution and 
taking the form of natural aqueducts and
 bridges4 ,in  ,carlsbad the numerous   
hot springs have deposited masses of    
pisolitic  rock 7,strudelstein7 which   
have filled up the whole bottom of the  
valley1 and upon these deposits the town
 itself is mainly built4  ,in ,central  
,italy the deposits of travertine formed
 by calcareous  springs are of enormous 
extent and thickness3 ,st4 ,peter's and 
all the  principal buildings of ,rome   
being constructed of this travertine or 
',tibur-stone4'    ,sidenote3           

,,formation ,,of ,,sinter-,,terraces4   
,when springs charged with silica or    
carbonate of lime rise upon the  slope  
of a hill composed of loose volcanic    
materials1 they give rise  to the       
remarkable structures known as sinter-  
and travertine-terraces  7see fig4 #hj74
 ,the water flowing downwards from the  
vent forms a  hard deposit upon the     
lower slope of the hill1 while the      
continual  deposition of solid materials
 within the vent tends to choke it up4  
,as a new vent cannot be forced by the  
waters through the hard rock  formed    
below1 it is originated a little higher 
up4 ,thus the site of the  spring is    
gradually shifted farther and farther   
back into the hill4 ,as  deposition     
takes place along the surfaces over     
which this water flows1  terraces are   
built up enclosing basins4 ,of          
structures of this kind we  have        
remarkable examples in the              
sinter-terraces of ,rotomahana in ,new  
,zealand and the travertine-terraces of 

the ,gardiner's ,river in the           
,yellowstone ,park district of the      
,rocky ,mountains4    ,illustration3    
,fig4 #hj4--;,diagram illustrating the  
mode of formation of  ,travertine and   
,sinter ,terraces on the sides of a hill
 of tuff4          ,,chapter ,,vii4     
,,the ,,succession ,,of ,,operations    
,,taking ,,place ,,at ,,volcanic        
,,centres4      ,that a volcanic vent1  
when once established1 may display      
intense  activity during enormous       
periods of time1 there cannot be the    
smallest  reason for doubting2 for the  
accumulation of materials around some   
existing volcanic centres must certainly
 have been going on during  many        
thousands1 perhaps millions1 of years4  
,to us1 whose periods of  observation   
are so circumscribed1 it may therefore  
at first sight  appear a hopeless task  
to trace the 'life-history of a         
volcano1' to  discover the stages of its
 development1 and to indicate the       
various  episodes which have occurred   

during the long periods it has been in  
existence4 ,but when it is remembered   
that we have the opportunity of         
studying and comparing hundreds of such 
volcanoes1 exhibiting every  varying    
phase of their development1 we shall see
 that such an attempt  is by no means so
 unpromising as it at first sight       
appears to be4 ,in  the present chapter1
 we shall give an account of the results
 which have  already been obtained by   
inquiries directed to this object4      
,sidenote3 ,,cycles ,,of ,,volcanic     
,,phenomena4    ,there is not the       
smallest room for doubt that during the 
past history  of our globe1 exhibitions 
of subterranean energy have occurred at 
many  different parts of its surface4   
,there is further evidence that at the  
several sites where these displays of   
the volcanic forces have taken  place1  
the succession of the outbursts has run 
through a regular cycle1  gradually     
increasing in intensity to a maximum1   
and then as gradually  dying away4    ,a

 little consideration will show that the
 first portion of this cycle  of events 
is the one which it is most difficult to
 examine and study4  ,the products of   
the earlier and feeble displays of      
volcanic activity1  at any particular   
centre1 are liable to be destroyed1 or  
masked1 during  the ejection of         
overwhelming masses of materials in the 
later stages  of its more matured       
energy4 ,that the feeble displays of    
volcanic  force now exhibited in some   
localities will gradually increase in   
intensity in the future1 and eventually 
reach the grandest stage of             
development1 there can be no reason for 
doubting4 ,but1 unfortunately1  we are  
quite unable to discriminate these      
feeble manifestations1 which  are the   
embryonic stages in the development of  
grand exhibitions of  the volcanic      
forces1 from slight outbursts which die 
away and make no  farther sign4    ,from
 what has been proved concerning the    
true nature of volcanic  action1        

however1 it is certain that the first   
step towards the  exhibition of such    
action1 at any particular locality1 must
 be the  production of an aperture in   
the earth's crust4 ,only by means of    
such an aperture can the vapours1 gases1
 and rocky materials reach  the surface1
 and give rise to the phenomena there   
displayed4 ,there is  reason to believe 
that all such apertures are really of   
the nature of  fissures1 or cracks1     
which have been opened through the      
superjacent  strata by the efforts of   
the repressed subterranean forces4      
,some recent writers have1 it is true1  
endeavoured to draw a distinction       
between what they call                  
'fissure-eruptions1' and eruptions      
taking  place from volcanic cones4 ,but 
all volcanic outbursts are truly        
'fissure-eruptions'--the subterranean   
materials finding their way to  the     
surface through great cracks1 which1 in 
a more or less vertical  position1      
traverse the overlying rock-masses4 ,it 

is true that in many  cases portions of 
these cracks soon get choked up1 while  
other portions  become widened1 and the 
volcanic energy is concentrated at such 
spots4  ,thus the materials ejected from
 these fissures are usually emitted in  
greatest quantities at one or more      
points along the fissure1 and a  single 
great volcanic vent1 or a row of smaller
 vents1 is established  upon the line at
 which the fissure reaches the surface4 
,we have seen that the amount of        
explosive action taking place at        
different volcanic vents varies         
according to the proportion of          
imprisoned water contained in the lava4 
,in the cases where there is  much      
explosive action1 vast accumulations of 
scori1 lapilli1 and  dust take place1   
and cones of great size are built up2   
but in those  cases where the explosive 
action is small the lavas flow quietly  
from  the vent1 and only small          
scori-cones are thrown up1 these being  
probably soon swept away by the         

lava-currents themselves or by denuding 
agencies4 ,but both kinds of eruption   
have equal claims to be called          
'fissure-eruptions4'    ,sidenote3      
,,formation ,,of ,,volcanic ,,fissures4 
,in the expansive force of great masses 
of imprisoned vapour1 we have  a        
competent cause for the production of   
the fissures through which  volcanic    
outbursts take place4 ,such fissures are
 found traversing the  rocks lying above
 volcanic foci1 and often extending to  
distances of  many miles1 or even       
hundreds of miles1 from the centres of  
activity4  ,some of these cracks are    
found to be injected with fused         
materials from  below1 others have been 
more or less completely filled with     
various  minerals that have been        
volatilized1 or carried by superheated  
waters  from the deeper regions of the  
earth's crust4 ,that many of the cracks 
thus produced in the superjacent rocks1 
by the heaving forces of  imprisoned    
vapour seeking to escape1 never reached 

the surface1 we have  sufficient proof  
in many mining regions4    ,if we now   
transfer our attention from the deeper  
portions of the  earth's crust to the   
surface1 we can well understand how the 
attempts  of the imprisoned vapours to  
force a passage for themselves through  
the  solid rock-masses would lead to    
shocks and jars among the latter4 ,each 
of these shocks or jars would give rise1
 in the surrounding portions  of the    
earth's crust1 to those vibrations which
 we know as earthquakes4  ,the close    
connection between most earthquakes and 
volcanic phenomena is  a fact that does 
not admit of the smallest doubt2 and    
though it would  be rash to define all  
earthquakes as 'uncompleted efforts to  
establish  a volcano1' yet1 in the      
efforts of the repressed subterranean   
forces to  find a vent by the production
 of fissures in the overlying           
rock-masses1  we have a cause competent 
to the production of those shocks which 
are  transmitted to such enormous       

distances as waves of elastic           
compression4    ,we have seen that the  
production of the fissure upon which the
 small  volcano of ,monte ,nuovo was    
thrown up was preceded by a succession  
of earthquakes1 which for a period of   
over two years terrified the            
inhabitants of the district1 and might  
have warned them of the  coming event4  
,in the same manner1 doubtless1 the     
period before the  appearance of        
volcanic phenomena in a new area would  
be marked by  powerful subterranean     
disturbances within it1 due to the      
efforts of the  imprisoned vapours to   
force for themselves a channel to the   
surface4    ,sidenote3 ,,nature ,,of    
,,first ,,ejections ,,from ,,fissures4  
,in the case of ,monte ,nuovo1 we have  
seen that the fissure1 when  produced1  
emitted water--at first in a cold1 then 
in a boiling  condition--and1           
eventually1 steam and scori4 ,it is     
probable that  through the first cracks 
which reached the surface1 during the   

heaving  of the subterranean forces1    
water1 charged with carbonic acid1      
flowed  abundantly1 and that these cold 
springs1 charged with carbonic acid  and
 carbonate of lime1 would be succeeded  
by others which were hot  and contained 
silica in solution4 ,in ,hungary1 the   
,western ,isles of  ,scotland1 and many 
other volcanic districts1 we find       
abundant evidence  that1 before the     
eruption of lavas in the area1 great    
masses of  travertine and siliceous     
sinter were formed by the action of cold
 and  hot springs4    ,as the volcanic  
action became more intense by the more  
perfect opening  of the fissures1 the   
evolution of carbonic add gas would be  
succeeded  by the appearance of         
sulphurous acid1 sulphuretted hydrogen1 
boracic  acid1 and hydrochloric acid1   
which recent studies have shown to be   
successively emitted from volcanic vents
 as the temperature within them  rises4 
,at last lava or molten rock becomes    
visible within the fissures1  and the   

ejection of the frothy masses--scori1   
pumice1 lapilli and  dust--commences1   
and this is sometimes succeeded by the  
outflow of  currents of lava4    ,that  
volcanoes originate upon lines of       
fissure in the earth's crust  we have   
the most convincing proofs4 ,not only   
have such fissures been  seen in actual 
course of formation at ,vesuvius1 ,etna1
 and other active  volcanoes1 but a     
study of the volcanoes dissected by     
denudation affords  the most convincing 
evidence of the same fact4 ,the         
remarkable linear  arrangement seen in  
groups of volcanoes1 which is           
conspicuous to the  most superficial    
observer1 confirms this conclusion4     
,illustration3 ,fig4 #ha4--,map of the  
volcanic group of the ,lipari  ,islands1
 illustrating the position of the lines 
of fissure on which the  volcanoes have 
been built up4    ,sidenote3 ,,shifting 
,,of ,,vents ,,along ,,fissures4    ,we 
have described the action going on at   
,stromboli as typical of that  which    

occurs at all volcanic vents4 ,stromboli
 is1 however1 one among  a group of     
islands all of which are entirely of    
volcanic origin4 ,the  volcanoes of this
 group of islands1 the olian or ,lipari 
,islands1 are  arranged along a series  
of lines which doubtless mark fissures  
in the  earth's crust4 ,these fissures1 
as will be seen by the accompanying map 
7fig4 #ha71 radiate from a centre at    
which we have proofs of the former      
existence of a volcano of enormous      
dimensions4 ,it is a very interesting   
fact1 which the studies of ,prof4 ,suess
 have established1 that the  earthquakes
 which have so often desolated ,calabria
 appear to have  originated immediately 
beneath this great centre of volcanic   
activity4    ,illustration3 ,fig4       
#hb4--,the ,puy de ,pariou in the       
,auvergne1  illustrating the shifting of
 the centre of eruption along a line of 
fissures4    ,when two volcanic cones   
are thrown up on the same line of       
fissure1  their full development is     

interfered with1 and irregularities in  
their  form and characters are the      
consequence4 ,in the plan 7fig4 #hb7 and
 the  section 7fig4 #hc7 an example is  
given of the results of such a shifting 
of the centre of eruption along a line  
of fissure4 ,by the second  outburst1   
one-half of the first-formed cone has   
been removed1 and the  second-formed    
overlaps the first4    ,illustration3   
,fig4 #hc4--;,ideal section of the ,puy 
de ,pariou4    ,sometimes a number of   
scoria- or tuff-cones are thrown up in  
such close  proximity to one another    
along a line of fissure1 that they merge
 into  a long irregular heap on the     
summit of which a number of distinct    
craters can be traced4 ,an example of   
this kind was furnished by the  line of 
scoria-cones formed above the fissure   
which opened on the  flanks of ,etna in 
#ahfe 7see fig4 #hd74    ,illustration3 
,fig4 #hd4--;,fissure formed on the     
flanks of ,etna during  the eruption of 
#ahfe4    a4 ,monte ,frumento1 an old   

parasitic cone4 b4 ,line of fissure4 c1 
c1 c4 ,new scoria-cones thrown up on    
line of fissure4 d4 ,lava from  same4   
,illustration3 ,fig4 #he4--,plan of the 
,island of ,vulcano1 based on the  map  
of the ,italian ,government4            
,sidenote3 ,,shifting ,,of ,,eruptions  
,,along ,,fissures4    ,even in the case
 of great composite cones1 however1 we  
sometimes find  proofs of the centre of 
eruption having shifted its place along 
the  line of fissure4 ,no better example
 of this kind could possibly be  adduced
 than that of the ,island of ,vulcano1  
with the peninsula of  ,vulcanello1     
which is joined to it by a narrow       
isthmus 7see the map1  fig4 #ha1 p      
#aib74 ,in fig4 #he we have given an    
enlarged plan of this  island which will
 make its peculiar structure more       
intelligible 7see  also the section     
given in fig4 #gg1 ,no4 #f1 facing p4   
#agh74    ,the south-eastern part of the
 island consists of four crater-rings1  
one half of each of ,which has been     

successively destroyed1 through  the    
shifting of the centre of eruption      
towards the north-west1 along  the great
 line of fissure shown in the general   
map 7fig4 #ha74 ,the  last formed of    
these four crater-rings is the one which
 is now most  complete1 and culminates  
in ,monte ,saraceno 7#aeha ft471 a in   
the  plan1 the highest point in the     
island4 ,the older crater-rings have    
been in part removed by the inroads of  
the waters of the ,mediterranean  on the
 shores of the island4 ,in the centre of
 the great crater1  b1 which we have    
just described1 rises the present active
 cone of  ,vulcano1 #a1bff feet high1   
and having a crater1 c1 about #fjj yards
  in diameter and more than #ejj feet in
 depth4 ,from this cone1 a great  stream
 of obsidian1 e1 flowed in the year     
#agge1 and a small crater1  d1 the      
,fossa ,anticha1 has been opened in the 
side of the cone4 ,the  continuation of 
the same line of fissure is indicated by
 a ruined  tuff-cone1 f1 known as the   

,faraglione1 and the three scoria-cones 
of  ,vulcanello1 g1 h1 which have been  
thrown up so close to one another  as to
 have their lower portions merged in one
 common mass1 as shown in  fig4 #hf4    
,sidenote3 ,,systems ,,of ,,volcanic    
,,fissures4    ,even in volcanoes of the
 largest dimensions we sometimes find   
proofs of  the centre of eruption having
 shifted along the line of fissure4     
,lyell  showed that such a change in the
 position of the central axis of the    
volcano had taken place in ,etna1 and   
the same phenomenon is exhibited  in the
 clearest manner' by some of the ancient
 volcanoes of the ,inner  ,hebrides1    
which have been dissected by the        
denuding forces4    ,illustration3 ,fig4
 #hf4--,vulcanello1 with its three      
craters4    a4 ,the most recently-formed
 and perfect crater1 b and c4 ,older    
craters1 the walls of which have been   
partly removed by denudation1  e4       
,lava-currents proceeding from b4 ,the  
section exposed in the  cliff at d is   

represented in fig4 #ce1 p4 #aaf4    ,in
 the case of the ,lipari ,islands1 the  
fissures along which the  volcanic      
mountains have been thrown up radiate   
from a common centre1  and a similar    
arrangement can be traced in many       
volcanic regions1  especially those in  
which a great central volcano has       
existed4 ,in other  cases1 however1 as  
in the ,campi ,phlegri1 the volcanic    
vents appear  to be formed along lines  
which assume a parallel arrangement1 and
  this doubtless marks the relative     
position of the original fissures       
produced in the earth's crust when these
 volcanoes were formed4 ,in some  other 
cases we find evidences of the existence
 of a principal fissure  from the sides 
of which smaller cracks originated4     
,these three kinds of  arrangements of  
volcano-producing fissures are equally  
well illustrated  when we study those   
denuded districts1 in which1 as we have 
seen1 the  ground-plans of volcanic     
structures are revealed to our view4    

,there is now good ground for believing 
that in volcanic vents1 at which        
long-continued eruptive action takes    
place1 the lavas of different  chemical 
composition make their appearance in    
something like a definite  order4 ,it   
had been remarked by ,scrope and other  
geologists at the  beginning of the     
present century1 that in many volcanic  
areas the acid  or trachytic lavas were 
erupted before the basic or basaltic4   
,von ,richthofen1 by his studies in     
,hungary and the volcanic districts  of 
the ,rocky ,mountains1 has been able to 
enunciate a law governing the  natural  
order of succession of volcanic         
products2 and although some  exception  
to this law may be mentioned1 it is     
found to hold good for  many other      
districts than those in which it was    
first determined4    ,in a great number 
of cases it has been found that the     
first erupted  rocks in a volcanic      
district are those of intermediate      
composition  which are known as         

andesites4 ,these andesites1 which are  
especially  characterised by the nature 
of their felspar1 sometimes contain free
  quartz and are then known as          
quartz-andesites or dacites1 from their 
abundance in ,transylvania1 the old     
,roman province of ,dacia4    ,sidenote3
 ,,order ,,of ,,eruption ,,of ,,volcanic
 ,,products4    ,von ,richthofen        
suggests that another class of volcanic 
rocks1 to which  he gives the name of   
'propylites1' were in every case erupted
 before  the andesites1 and in support  
of his views adduces the fact that in   
many instances propylites are found     
underlying andesites4 ,but the          
propylites are1 in chemical composition1
 identical with the andesites1  and like
 them present some varieties in which   
quartz occurs1 and others  in which that
 mineral is absent4 ,in their           
microscopic characters the  propylites  
differ from the andesites and dacites   
only in the fact that  the former are   
more perfectly crystalline in structure1

 being indeed in  many cases quite      
undistinguishable from the diorites or  
the plutonic  representatives of the    
andesites4 ,the propylites also contain 
liquid  cavities1 which the andesites   
and dacites as a rule do not1 and the   
former class of rocks1 as ,prof4 ,szabo 
well points out1 are usually much       
altered by the passage of sulphurous and
 other vapours1 in consequence  of which
 they frequently contain valuable       
metallic ores4    ,the extrusion of     
these andesitic lavas is sometimes      
accompanied1 and  sometimes preceded or 
followed1 by eruptions of trachytic     
lavas--that  is1 of lavas of            
intermediate composition which have a   
different kind of  felspar from that    
prevailing in the andesites4    ,in the 
final stages of the eruptive action in  
most volcanic districts  the lavas      
poured forth belong to the classes of   
the rhyolitic or acid1  and the basaltic
 or basic lavas4    ,these facts are    
admirably illustrated in the case of the

 volcanic  district of the ,lipari      
,islands1 to which we have had such     
frequent  occasion to refer4 ,the great 
central volcano of this district1 which 
now in a ruined condition constitutes a 
number of small islets 7see  the map1   
fig4 #ha1 p4 #aib71 is composed of      
andesitic lavas4 ,the other  great      
volcanoes thrown up along the three     
radiating lines of fissure  are composed
 of andesitic and trachytic rocks4 ,but 
all the more recent  ejections of the   
volcanoes of the district have consisted
 either of  rhyolites1 as in ,lipari and
 ,vulcano1 or of basalts1 as in         
,stromboli and  ,vulcanello4    ,von    
,richthofen and the geologists who most 
strongly maintain the  generalisations  
which he has made concerning the order  
of appearance  of volcanic products1 go 
much farther than we have ventured to   
do1  and insist that in all volcanic    
districts a constant and unvarying      
succession of different kinds of lavas  
can be made out4 ,it appears to  us1    

however1 that the exceptions to the law1
 as thus precisely stated1  are so      
numerous as to entirely destroy its     
value4    ,the generalisation that in   
most volcanic districts the first       
ejected  lavas belong to the            
intermediate group of the andesites and 
trachytes1  and that subsequently the   
acid rhyolites and the basic basalts    
made  their appearance1 is one that     
appears to admit of no doubt1 and is    
found to hold good in nearly all the    
volcanic regions of the globe  which    
have been attentively studied4    ,the  
,tertiary volcanic rocks of our own     
country1 those of ,north  ,germany1     
,hungary1 the ,euganean ,hills1 the     
,lipari ,islands1 and many  other       
districts in the ,old ,world1 together  
with the widespread volcanic  rocks of  
the ,rocky ,mountains in the ,new       
,world1 all seem to conform to  this    
general rule4    ,sidenote3 ,,theory    
,,of ,,volcanic ,,magmas4    ,in        
connection with this subject1 it may be 

well to refer to the  ideas on the      
composition of volcanic rocks which were
 enunciated by  ,bunsen1 and the        
theoretic views based on them by        
,durocher4 ,bunsen  justly pointed out  
that all volcanic rocks might be        
regarded as  mixtures in varying        
proportions of two typical kinds of     
materials1  which he named the 'normal  
trachytic' and the 'normal pyroxenic'   
elements respectively4 ,the first of    
these corresponds very closely in       
composition with the acid volcanic rocks
 or rhyolites1 and the second  with the 
basic volcanic rocks or basalts4        
,durocher pointed out that  if          
quantities of these different materials 
existed in admixture1 the  higher       
specific gravity of the basic element   
would cause it gradually  to sink to the
 bottom1 while the acid element would   
rise to the top4  ,carrying out this    
idea still further1 he propounded the   
theory that  beneath the earth's solid  
crust there exist two magmas1 the upper 

consisting of light acid materials1 the 
lower of heavy basic ones2 and  he      
supposed that by the varying intensity  
of the volcanic forces we may  have     
sometimes one or the other magma erupted
 and sometimes varying  mixtures of the 
two4    ,the study of volcanic rocks in 
recent years has not lent much support  
to the theoretic views of ,durocher     
concerning the existence of two         
universal magmas beneath the earth's    
crust2 and there are not a few  facts   
which seem quite irreconcilable with    
such a theory4 ,thus we  find evidence  
that in the adjacent volcanic districts 
of ,hungary and  ,bohemia1 volcanic     
action was going on during the whole of 
the latter  part of the ,tertiary       
period4 ,but the products of the        
contemporaneous  volcanic outbursts in  
adjacent areas were as different in     
character  as can well be imagined4 ,the
 volcanic rocks all over ,hungary       
present  a strong family likeness2 the  
first erupted were trachytes1 then      

followed andesites and dacites in great 
abundance1 and lastly rhyolites  and    
basalts containing felspar4 ,but in     
,bohemia1 the lavas poured out  from the
 volcanoes during the same period were  
firstly phonolites  and then basalts    
containing nepheline and leucite4 ,it is
 scarcely  possible to imagine that such
 very different classes of lavas could  
have been poured out from vents which   
were in communication with the  same    
reservoirs of igneous rock1 and we are  
driven to conclude that the  ,hungarian 
and ,bohemian volcanoes were supplied   
from different sources4    ,sidenote3   
,,separation ,,of ,,lavas ,,in          
,,reservoirs4    ,but the undoubted fact
 that in so many volcanic regions the   
eruption of  andesitic and trachytic    
rocks1 which are of intermediate        
composition1  is followed by the        
appearance of the differentiated        
products1 rhyolite  and basalt1 which   
are of acid and basic composition       
respectively1 lends  not a little       

support to the view that under each     
volcanic district a  reservoir of more  
or less completely molten rock exists1  
and that in  these reservoirs various   
changes take place during the long      
periods  of igneous activity4 ,during   
the earlier period of eruption the      
heavier  and lighter elements of the    
contents of these subterranean          
reservoirs  appear to be mingled        
together2 but in the later stages of the
 volcanic  history of the district1 the 
lighter or acid elements rise to the    
top1  and the heavier or basic sink to  
the bottom1 and we have separate        
eruptions of rhyolite and basalt4 ,we   
even find some traces of this  action   
being carried still further4 ,among the 
basalts ejected from the  volcanoes of  
,northern ,germany1 ,bohemia1 ,styria1  
,auvergne1 and many  other regions1 we  
not unfrequently find rounded masses    
consisting of  olivine1 enstatite1      
augite1 and other heavier constituents  
of the rock4  ,these often form the     

centre of volcanic bombs1 and are not   
improbably  portions of a dense mass    
which may have sunk to the bottom of the
  reservoirs of basaltic materials4     
,in consequence of the circumstance that
 the eruption of lavas of  intermediate 
composition usually precedes that of    
other varieties1 we  usually find the   
central and older portions of great     
volcanoes to be  formed of andesites1   
trachytes1 or phonolites1 while the     
outer and  newer portions of the mass   
are made up of acid or basic lavas4     
,this is  strikingly exemplified in the 
great volcanoes of the ,auvergne and the
  ,western ,isles of ,scotland1 in all  
of which we find that great mountain    
masses have1 in the first instance1 been
 built up by extrusions of lava  of the 
intermediate types1 and that through    
this central core fissures  have been   
opened conveying basic lavas to the     
surface4 ,from these  fissures great    
numbers of basaltic lava-streams have   
issued1 greatly  increasing the height  

and bulk of the volcanic cones and      
deluging the  country all around4       
,the lavas of intermediate              
composition--the andesites1 trachytes1  
and  phonolites--possess1 as we have    
already seen1 but very imperfect        
liquidity as they flow from the volcanic
 vents4 ,hence we find them  either     
accumulating in great dome-shaped masses
 above the vent or  forming lava-streams
 which are of great bulk and thickness1 
but do not  flow far from the orifices  
whence they issue4 ,the more fusible    
basaltic  lavas1 on the other hand1     
spread out evenly on issuing from a     
vent1 and  sometimes flow to the        
distance of many miles from it4 ,this   
difference  in the behaviour of the     
intermediate and basic lavas is         
admirably  illustrated in the volcanic  
districts of the ,auvergne and the      
,western  ,isles of ,scotland4    ,in   
other cases1 like ,vesuvius1 we find    
that great volcanic cones of  trachytic 
tuff have been built up1 and that these 

masses of fragmentary  trachytic        
materials have been surrounded and      
enclosed by the ejection1  at a later   
date1 of great outbursts of basaltic    
lavas4 ,in still  other cases1 of which 
,rocca ,monfina in ,southern ,italy     
constitutes an  excellent example1 we   
find that a great crater-ring of        
trachytic tuffs  has been formed in the 
first instance1 and in the midst of this
 a cone1  composed of more basic        
materials1 has been thrown up4          
,sidenote3 ,,exceptions ,,to ,,the      
,,general ,,law4    ,in all these       
volcanoes we see the tendency towards   
the eruption  of intermediate lavas in  
the first instance1 and of basaltic and 
acid lavas at a later date4 ,valuable1  
however1 as are the early               
generalisations of ,scrope1 and the more
 precise law enunciated by ,von         
,richthofen concerning the 'natural     
order of succession of volcanic         
products1' we must not forget that there
 are to be found a considerable  number 

of exceptions to them4 ,there are some  
volcanic centres from  which only one   
kind of lava has been emitted1 and this 
may be either  acid1 basic1 or          
intermediate in composition2 and on the 
other hand1  there are districts in     
which various kinds of lava have been   
ejected  from the same vents within a   
short period of time1 in such a way as  
to  defy every attempt to make out      
anything like a law as to the order of  
their appearance4 ,nevertheless the     
rules which we have indicated appear  to
 hold good in so great a number of cases
 that they are well worthy  of being    
remembered1 and may serve as a basis on 
which we may reason  concerning the     
nature of the action going on beneath   
volcanic vents4    ,from the study of   
the external appearances of volcanic    
mountains1  combined with investigations
 of those which have been dissected by  
denudation1 we are able to picture to   
our minds the series of actions  by     
which the great volcanic mountains of   

the globe have been slowly and          
gradually built up4    ,in the first    
instance the eruptions appear to have   
taken place at  several points along a  
line of fissure1 but gradually all of   
these  would become choked up except one
 which became the centre of  habitual   
eruption4 ,from this opening1 ejections1
 firstly of lavas of  intermediate      
composition1 and afterwards of basic    
materials1 would take  place1 until a   
volcano of considerable dimensions was  
built up around  it4 ,but at last a     
point would be reached in the piling up 
of this  cone1 when the volcanic forces 
below would be inadequate to the work   
of raising the liquid lava through the  
whole length of the continually         
upward-growing tube of the volcano4     
,under these circumstances the          
expansive force of the imprisoned steam 
would find it easier to rend  asunder   
the sides of the volcanic cone than to  
force the liquid  material to the summit
 of the mountain4 ,if these fissures    

reached the  surface explosive action   
would take place1 in consequence of the 
escape  of steam from the glowing mass1 
and scoria-1 tuff-1 and lava-cones      
would be formed above the fissure4 ,in  
this way1 as we have already  pointed   
out1 the numerous 'parasitic cones'     
which usually abound on  the flanks of  
the greater volcanic mountains have been
 formed4 ,the  extrusion of these masses
 of scori and lava on the flanks of the 
mountain tends1 not only to increase the
 bulk of the mass1 but to  strengthen   
and fortify the sides4 ,for by the      
powerful expansive force  at work below1
 every weak place in the cone is        
discovered and a fissure  produced      
there2 but by the extrusion of material 
at this fissure1 and  still more by the 
consolidation of the lava in the        
fissure1 the weak  place is converted   
into one of exceptional strength4       
,sidenote3 ,,intrusive ,,masses         
,,beneath ,,volcanoes4    ,as the sides 
of the cone are thus continually        

repaired and strengthened  they are     
rendered more capable of withstanding   
the heaving forces  acting from below1  
and these forces can then only find vent
 for  themselves by again raising the   
liquefied lava to the central orifice   
of the mountain4 ,many volcanoes1 like  
,etna1 exhibit this alternation of      
eruptive action from the crater at the  
summit of the mountain1 and from        
fissures opened upon its flanks1 the    
former tending to raise the height  of  
the volcanic pile1 the latter to        
increase its bulk4    ,but at last a    
stage will be reached when the volcanic 
forces are  no longer able either to    
raise the lava up the long column of the
  central vent on the one hand1 or to   
rend asunder the strongly-built  and    
well-compacted flanks of the mountain on
 the other4 ,it is probably  under these
 conditions1 for the most part1 that the
 lavas find their  way between the      
masses of surrounding strata and force  
them asunder in  the way that we have   

already described4    ,in the case of   
the more fluid basaltic lavas1 as was   
pointed out so  long ago by ,macculloch1
 the liquefied materials may find their 
way  between the strata to enormous     
distances from the volcanic centre4     
,such  extended flat sheets of igneous  
rock retain their parallelism with the  
strata among which they are intruded    
over large areas1 and did not  probably 
produce any marked phenomena at the     
surface4    ,but in the case of less    
fluid lavas1 such as those of           
intermediate or  acid composition1 for  
example1 the effect would be far        
otherwise4 ,such  lavas1 not flowing    
readily from the centre of eruption1    
would tend to  form great bulky         
lenticular masses between the strata    
which they forced  asunder1 and1 in so  
doing1 could not fail to upheave and    
fissure the  great mountain-mass above4 
,vast lenticular masses of trachytic    
rock1  thus evidently forced between    
strata1 have been described by ,mr4 ,g4 

,k4 ,gilbert1 as occurring in the ,henry
 ,mountains of ,southern ,utah1 and  by 
him have been denominated 'laccolites1' 
or stone-cisterns4 ,whether  the great  
basaltic sheets1 like those described by
 ,macculloch1 and  those more bulky     
lenticular reservoirs of rock of which  
,mr4 ,gilbert  has given us such an     
admirable account1 were in all cases    
connected  with the surface1 may well be
 a matter for doubt4 ,it is quite       
possible  that1 in some cases1 liquefied
 masses of rocky materials in seeking   
to force their way to the surface only  
succeeded in thus finding a  way for    
themselves between the strata1 and their
 energy was expended  before the surface
 was reached and explosive action took  
place4 ,but it  is an undoubted fact    
that beneath many of the old volcanoes1 
of which  the internal structure is now 
revealed to us by the action of denuding
  forces1 great intrusive sheets and    
laccolites abound2 and we cannot  doubt 
that beneath volcanoes now in a state of

 eruption1 or in those  which have but  
recently become extinct1 similar        
structures must be in  course of        
formation4    ,sidenote3 ,,effects ,,of 
,,intrusion ,,beneath ,,cones4    ,that 
great upheaving forces have operated on 
volcanoes1 subsequently  to the         
accumulation of their materials1 we have
 sufficient evidence in  the ,val del   
,bove of ,etna1 the ,caldera of ,palma1 
the ,corral of ,madeira1  c4 ,in all of 
these cases we find a radial fissure    
7'barranco'7 leading  into a great      
crateral hollow2 and these radial       
fissures are of such  width and depth   
that their origin can only be referred  
to a disruptive  force like that which  
would be exercised by the intrusion of  
masses of  more or less imperfectly     
fluid material between the subjacent    
strata4  ,these facts1 of course1 lend  
no countenance to the views formerly    
held  by many geologists1 both in       
,germany and ,france1 that the materials
  of which volcanoes are built up were  

deposited in an approximately           
horizontal position1 and were           
subsequently blown up like a gigantic   
bubble4 ,in ,etna1 ,palma1 and ,madeira 
we find abundant proofs that the  mass  
existed as a great volcanic cone before 
the production of the  fissures         
7barrancos71 which we have referred to  
the force exercised  during the         
intrusion of great igneous masses       
beneath them4    ,but besides the       
horizontally-disposed intrusive sheets  
and laccolites1  great1 radiating1      
vertical fissures are produced by the   
heaving forces  acting beneath those    
volcanic centres which have been closed 
up and  'cicatrised' by the exudation   
from them of subterranean materials4    
,these vertical intrusions1 which we    
call dykes1 like the horizontal  ones1  
differ in character1 according to the   
nature of the materials  of which they  
are composed4 ,dykes of acid and        
intermediate lava are  usually of       
considerable width1 and do not extend to

 great distances  from the centres of   
eruption4 ,dykes composed of the        
more-liquid1 basic  lavas1 on the other 
hand1 may extend to the distance of     
hundreds of  miles from the central     
vent4 ,the way in which comparatively   
narrow1  basaltic dykes are found       
running in approximately straight lines 
for such enormous distances is a very   
striking fact1 and bears the  strongest 
evidence to the heaving and expanding   
forces at work at  volcanic centres1    
during and subsequently to the extrusion
 of the  igneous products at the        
surface4    ,these basaltic dykes occur 
in such prodigious numbers around some  
volcanic vents1 that the whole of the   
stratified rocks in the immediate       
vicinity are broken up by a complete    
network of them1 crossing and           
interlacing in the most complicated     
fashion4 ,farther away from the  vents1 
similar dykes are found in smaller      
numbers1 evidently radiating  from the  
same centre1 and sometimes extending to 

a distance of more  than a hundred miles
 from it4 ,nowhere can we find more     
beautiful  illustrations of such dykes  
than in the ,western ,isles of          
,scotland4 ,when  composed of materials 
which do not so easily undergo          
decomposition as  the surrounding rocks1
 they stand up like vast walls2 but     
when1 on the  other hand1 they are more 
readily acted on by atmospheric moisture
 than  are the rocks which enclose them1
 they give rise to deep trenches with   
vertical sides1 which render the country
 almost impassable4    ,sidenote3       
,,structure ,,of ,,intrusive ,,masses4  
,the lava consolidating in these        
horizontal intrusions 7sheets and       
laccolites71 and the vertical intrusions
 7dykes71 is usually more  crystalline  
in structure than the similar materials 
poured out at the  surface4 ,in the same
 dyke or sheet1 when it is of great     
width1 we  often find every             
variation--from a glassy material formed
 by the rapid  cooling of the mass where

 it is in contact with other rocks1 to  
the  perfectly crystalline or granitic  
varieties which form the centre of  the 
intrusion4 ,it is in these dykes and    
other intrusions that we find  the most 
convincing evidence of the truth of the 
conclusions1 which  we have enunciated  
in a former chapter1 concerning the     
dependence of  the structure of an      
igneous rock upon the conditions under  
which it  has consolidated4 ,one        
material is found1 under varying        
conditions1  assuming the characters of 
obsidian1 rhyolite1 quartz-felsite1 or  
granite2 another1 under the same set of 
conditions1 taking the form of          
tachylyte1 basalt1 dolerite1 and gabbro4
    ,that these great intrusive masses1 
sheets and dykes1 in their passage      
between the sedimentary rocks sometimes 
find places where the overlying  strata 
are of such thinness or incoherence that
 the liquefied rocks are  able to force 
a way for themselves to the surface1 we 
have the clearest  proof4 ,in some dykes

 we find the rock in their upper        
portions losing  its compact character  
and becoming open and scoriaceous1      
showing that  the pressure had been so  
far diminished as to allow of the       
imprisoned  water flashing into steam4  
,all round great volcanoes which have   
become extinct we frequently find       
series of small volcanic cones1 which   
have evidently been thrown up  along the
 lines where the great lava-filled      
fissures1 which we have  been           
describing1 have reached the surface and
 given rise to explosive  action there4 
,the linear arrangement of these small  
cones1 which are  thrown up in the      
plains surrounding vast volcanic        
mountains that have  become extinct1 is 
very striking4 ,the numerous 'puys' of  
the ,auvergne  and adjoining volcanic   
regions of ,central ,france are for the 
most part  small scoria- and lava-cones 
which were thrown up along great lines  
of fissure radiating from the immense1  
central1 volcanic mountains of  the     

district1 after they had become extinct4
 ,these scoria-cones and  the small     
lava-streams which flow from them1 as   
was so well shown by  ,mr4 ,scrope1 mark
 the latest efforts of the volcanic     
forces beneath the  district before they
 finally sank into complete extinction4 
,in the  ,western ,isles of ,scotland1  
as ,i have elsewhere shown1 we can study
 the  formation of these later-formed   
cones in the plains around extinct      
volcanic mountains1 with the additional 
advantage of having revealed  to us1 by 
the action of the denuding forces1 their
 connection with the  great radiating   
fissures4    ,it has been shown that the
 several stages in the decline of each  
volcanic outburst is marked by the      
appearance at the vent of certain  acid 
gases4 ,in the same way1 after the      
ejection of solid materials  from a     
volcanic vent has come to an end1       
certain gaseous substances  continue to 
be evolved2 and as the temperature at   
the vents declines1  the nature of the  

volatile substances emitted from them   
undergoes a  regular series of changes4 
,sidenote3 ,,order ,,of ,,emission ,,of 
,,volcanic ,,gases4      ,m4 ,fouqu1 by 
a careful series of analyses of the     
gases which he  collected at different  
gaseous vents1 or fumaroles as they are 
called1  in the crater of ,vulcano1 has 
been able to define the general         
relations  which appear to exist between
 the temperature at a volcanic orifice  
and the volatile substances which issue 
from it4 ,he found that in  fumaroles1  
in which the temperature exceeded #cfj  
centigrade1 and  in which in consequence
 strips of zinc were fused by the stream
 of  issuing gas1 the analysis of the   
products showed sulphurous acid and     
hydrochloric add to be present in large 
quantities1 and sulphuretted  hydrogen  
and carbonic acid in much smaller       
proportions4 ,around these  excessively 
heated fumaroles1 the lips of which     
often appear at night  to be red-hot1   
considerable deposits of sulphide of    

arsenic1 chloride  of iron1 chloride of 
ammonium1 boracic acid1 and sulphur were
 taking  place4    ,it was found1       
however1 that as the temperature of the 
vent declined1  the emission of the     
sulphurous acid and hydrochloric acid   
diminished1  and the quantity of        
sulphuretted hydrogen and carbonic acid 
mingled  with them was proportionately  
increased4    ,in the same way it       
appears to be a universal rule that when
 a volcanic  vent sinks into a condition
 of temporary quiescence or complete    
extinction the powerfully acid gases1   
hydrochloric acid and sulphurous  acid1 
make their appearance in the first      
instance1 and at a later stage  these   
are gradually replaced by sulphuretted  
hydrogen and carbonic acid4    ,of these
 facts we find a very beautiful         
illustration in the ,campi  ,phlegri    
near ,naples4 ,with the exception of    
,monte ,nuovo1 the volcano  which has   
most recently been in a state of        
activity in that district  is the       

,solfatara4 ,from certain apertures in  
the floor of the crater of  the         
,solfatara there issue continually      
watery vapours1 sulphurous acid1        
sulphuretted hydrogen1 hydrochloric     
acid1 and chloride of ammonium4  ,the   
action of these substances upon one     
another1 and upon the volcanic  rocks   
through which they pass1 gives rise to  
the formation of certain  chemical      
products which1 from a very early       
period1 have been collected  on account 
of their commercial value4 ,the action  
of these add gases  upon the surrounding
 rocks is very marked2 efflorescent     
deposits of  various sulphates and      
chlorides take place in all the crevices
 and  vesicles of the rock2 sulphur and 
sulphide of arsenic are also formed  in 
considerable quantities2 and the        
trachytic tuffs1 deprived of their      
iron-oxide1 alkaline earths and         
alkalies1 which are converted into      
soluble sulphates and chlorides1 are    
reduced to a white1 powdery1  siliceous 

mass4 ,many volcanoes1 which have sunk  
into a state of  quiescence or          
extinction like the ,solfatara of       
,naples1 exhibit the same  tendency to  
give off great quantities of the        
powerfully-acid gases  which act upon   
the surrounding rocks1 and deprive them 
of their colour  and consistency4 ,such 
volcanoes are said by geologists to have
 sunk  into the 'solfatara stage4'      
,sidenote3 ,,solfatara-,,stage ,,of     
,,volcanoes4    ,at the ,lake of ,agnano
 and some other points in the ,campi    
,phlegri1  however1 we find fissures    
from which the less-powerfully acid     
gases1  sulphuretted hydrogen and       
carbonic acid1 issue4 ,these gases as   
they1  are poured forth from the vents  
are found to be little1 if at all1      
above the temperature of the atmosphere4
 ,sulphuretted hydrogen is an           
inflammable gas1 and in the so-called   
salses and mud-volcanoes1 at  which it  
is ejected in considerable quantities1  
it not unfrequently  takes fire and bums

 with a conspicuous flame4 ,carbonic    
acid on account  of its great density   
tends to accumulate in volcanic fissures
 and  craters rather than to mingle with
 the surrounding atmosphere4 ,at the    
so-called ,grotto del ,cane1 beside the 
,lago ,agnano1 it is the custom to  show
 the presence of this heavy and         
suffocating gas by thrusting a dog  into
 it1 the poor animal being revived1     
before life is quite extinct1  by       
pouring cold water over it4 ,at the     
,bdos ,hegy or 'stinking hill' of       
,transylvania1 carbonic acid and        
sulphuretted hydrogen are emitted in    
considerable quantities1 and it is      
possible to take a bath of the heavy    
gas1 the head being kept carefully above
 the constant level of the  exhalations4
    ,although the stories of the ancient
 ,avernian lake1 across which no bird   
could fly without suffocation1 and of   
the ,guevo ,upas1 or ,poison ,valley  of
 ,java1 which it has been said no living
 being can cross1 may not  improbably be

 exaggerations of the actual facts1 yet 
there is a basis  of truth in them in   
the existence of old volcanic fissures  
and craters  which evolve the poisonous 
sulphuretted hydrogen and carbonic acid 
gases4    ,besides the gases which we   
have already named1 and which are the   
most  common at and characteristic of   
volcanic vents1 there are some others   
which are not unfrequently emitted4     
,first among these we must mention      
boracic acid1 which1 though not a       
remarkably volatile substance1 is       
easily carried along in a fine state of 
division in a current of steam4  ,at    
,monte ,cerboli and ,monte ,rotondo in  
,tuscany1 great quantities of  steam    
jets accompanied by sulphuretted        
hydrogen and boracic acid issue  from   
the rocks1 and these jets being directed
 into artificial basins of  water1 the  
boracic acid is condensed and is        
recovered by evaporation4  ,we have     
already noticed that boracic add is     
evolved with the gases at  ,vulcano and 

other craters2 and the part which this  
substance plays in  volcanic districts  
is shown by the fact that many of the   
rocks1 filling  old subterranean        
volcanic reservoirs1 are found to be    
greatly altered  and to have new        
minerals developed in their midst       
through the action  upon them of boracic
 acid4    ,ammonia and various compounds
 of carbon1 nitrogen1 and hydrogen are  
among the gases evolved from volcanic   
vents4 ,in some cases these gases  may  
be produced by the destructive          
distillation of organic materials  in   
the sedimentary rocks through which     
volcanic outbursts take place4  ,but it 
is far from impossible that under the   
conditions of temperature  and pressure 
which exist at the volcanic foci1 direct
 chemical union  may take place between 
substances1 which at the surface appear 
to be  perfectly inert in each other's  
presence4    ,when the temperature at   
volcanic fissures is no longer          
sufficiently  high to cause water to    

issue in the condition of vapour or     
steam1 as is  the case at the 'stufas'  
which we have described1 it comes forth 
in the  liquid state4 ,water so issuing 
from old volcanic fissures may vary in  
its temperature1 from the boiling point 
downwards4    ,sidenote3 ,,geysers ,,and
 ,,hot-,,springs4    ,when the water    
issues at a temperature little removed  
from the boiling  point1 it is apt to   
give rise to intermittent springs or    
geysers1 the  eruptions of which exhibit
 a remarkable analogy with those of     
ordinary  volcanoes4 ,geysers may indeed
 be described as volcanoes in which     
heated  water1 instead of molten rock1  
is forced out from the vent by the      
escaping steam4 ,they occur in great    
abundance in districts in which the     
subterranean action is becoming dormant 
or extinct1 such as ,iceland1  the      
,north ,island of ,new ,zealand1 and the
 district of the ,national ,park  in the
 ,rocky ,mountains4    ,many attempts   
have been made to explain the exact     

mechanism by which  the intermittent    
action of geysers is produced1 but it is
 not at all  probable that any one such 
explanation will cover all the varied   
phenomena exhibited by them4 ,like      
volcanic outbursts1 geyser eruptions    
doubtless originate in the escape of    
bubbles of steam through a liquid  mass1
 and this liberation of steam follows   
any relief of pressure4  ,in districts  
where vast masses of lava are slowly    
cooling down from  a state of           
incandescence1 and surface waters are   
finding their way  downwards while      
subterranean waters are finding their   
way upwards1  there can be no lack of   
the necessary conditions for such       
outbursts4  ,sometimes the eruptions of 
geysers take place at short and regular 
intervals1 at other times they occur at 
wide and irregular intervals  of time4  
,in some cases the outbursts take place 
spontaneously1 and at  others the action
 can be hastened by choking up the vent 
with stones or  earth4    ,other hot    

springs1 like the ,strudel of ,carlsbad1
 rise above the surface  in a constant  
jet1 while most of them issue quietly   
and flow like  ordinary springs4        
,although the violent and paroxysmal    
outbursts of volcanic mountains  arrest 
the attention1 and powerfully impress us
 with a sense of the  volcanic activity 
going on beneath the earth's surface1   
yet it may  well be doubted whether the 
quantity of heat1 which the earth gets  
rid  of by their means1 at all          
approaches in amount that which is      
quietly  dissipated by means of the     
numerous 'stufas1' gaseous exhalations1 
and  thermal springs which occur in such
 abundance all over its surface4  ,for  
while the former are intermittent in    
their action1 and powerful  outbursts   
are interrupted by long periods of rest1
 the action of the  latter1 though      
feeble1 is usually continuous4          
,sidenote3 ,,effects ,,of               
,,hot-,,springs4    ,most people may    
regard the hot spring of ,bath as a very

 slight  manifestation of volcanic      
activity4 ,this spring issues at a      
constant  temperature of #di ,c1 or #abj
 ,fahr4 ,as1 however1 no less than      
#ahj1jjj  gallons of water issue daily  
from this source1 we may well understand
  how great is the amount of heat of    
which the earth's crust is relieved  by 
its agency4 ,it may indeed be doubted   
whether its action in this way  is not  
at least equal to that of a considerable
 volcano which1 though  so much more    
violent1 is intermittent in its action4 
,nor are thermal springs by any means   
ineffective agents in bringing          
materials from the interior of the      
earth's crust and depositing it  at the 
surface4 ,the ,bath spring contains     
various saline substances1  principally 
sulphates and chlorides1 in solution in 
its waters4 ,these  are quietly carried 
by rivers to the sea1 and are lost to   
our view4 ,the  spring has certainly    
maintained its present condition since  
the time  of the ,romans1 and ,i find   

that if the solid materials brought from
 the  interior of the earth during the  
last #b1jjj years had been collected1   
they would form a solid cone equal in   
height to ,monte ,nuovo4 ,yet we        
usually regard the ,campi ,phlegri as a 
powerfully-active volcanic  district1   
and the subterranean action in our own  
country as quite  unworthy of notice4   
,when we remember the fact that on the  
continent of ,europe the hot and  saline
 springs may be numbered by thousands1  
and that they especially  abound in     
districts like ,hungary1 the ,auvergne1 
the ,rhine provinces1  and ,central     
,italy1 where volcanic action has       
recently become extinct1  we shall be   
able to form some slight idea of the    
work performed  by these agents1 not    
only in relieving the earth's crust of  
its  superfluous heat1 but in           
transporting materials in a state of    
solution  from the interior of that     
crust and depositing them at the        
surface4 ,the  vast deposits of         

siliceous sinter and of travertine also 
bear witness  to the effects produced by
 hot and mineral springs4    ,nor is the
 work of these springs confined to the  
surface4 ,mr4 ,john  ,arthur ,phillips  
has shown that metallic gold and the    
sulphide of  quicksilver 7cinnabar7 have
 been deposited with the silica and     
other  minerals formed on the sides of a
 fissure from which hot springs issue   
at the surface4 ,there cannot be any    
doubt that the metallic veins or  lodes1
 which are the repositories of most of  
the metals employed in the  arts1 have  
been formed in cracks connected with    
great volcanic foci1  the transfer of   
the various sulphides1 oxides1 and salts
 which fill  the vein having been       
effected either by solution1            
sublimation1 or the  action of powerful 
currents of steam4    ,as the igneous   
activity of the district declines1 the  
temperature  of the issuing gases and   
waters diminishes with it1 until at last
  the volcanic forces appear to wholly  

abandon that region and to be           
transferred to another4    ,yet even    
after all or nearly all indications of  
the volcanic agencies  cease to make    
themselves visible at the surface1      
occasional tremblings  of the earth's   
crust show that perfect equilibrium has 
not been  restored below1 but that      
movements are taking place which result 
in  shocks that are transmitted through 
the overlying and surrounding           
rock-masses as earthquake vibrations4   
,sidenote3 ,,nature ,,of ,,volcanic     
,,cycles4    ,such is the cycle of      
changes which appears to take place at  
each  district of the earth's surface1  
as it successively becomes the scene  of
 volcanic activity4    ,the invasion of 
any particular area of the earth's      
surface by the  volcanic forces appears 
to be heralded by subterranean shocks   
causing  earthquake vibrations4         
,presently the origination of fissures  
is  indicated by the rise of saline and 
thermal springs1 and the issuing  of    

carbonic acid and other gases at the    
surface4 ,as the subterranean  activity 
becomes more pronounced1 the temperature
 of the springs and  emitted gases is   
found to increase1 and at last a visible
 rent is  formed at the surface1        
exposing the incandescent materials     
below4    ,from this open fissure which 
has thus been formed1 the gas and       
vapours  imprisoned in the incandescent 
rock-materials escape with such violence
  as to disperse the latter in scori and
 dust1 or to cause them to  well out in 
great streams as lava-flows4 ,usually   
the action becomes  concentrated at one 
or several points at which the ejected  
materials  accumulate to form volcanic  
cones4    ,sometimes the volcanic       
activity dies away entirely after these 
cones  are thrown up along the line of  
fissure1 but at others some such  centre
 becomes for a longer or shorter time   
the habitual vent for the  volcanic     
forces in the district1 and by repeated 
ejections of lavas and  fragmentary     

materials at longer or shorter intervals
 the cone increases  both in height and 
bulk4    ,when the height of the cone   
has grown to a certain extent1 it       
becomes  more easy for the volcanic     
energies below to rend the sides of the 
cone than to raise the molten materials 
to its summit4 ,in this way  lateral or 
parasitic cones are thrown up on the    
flanks of the volcanic  mountain1 the   
mass being alternately elevated and     
strengthened by the  ejections from the 
summit and sides respectively4    ,when 
the volcanic energies no longer suffice 
to raise the fluid  materials to the    
summit1 nor to rend the sides of the    
volcano1 fissures  with small cones may 
be formed in the plains around the great
 central  volcano4    ,at last1 however1
 this energy diminishes so far that rock
 materials  can no longer be forced to  
the surface1 the fissures become sealed 
up  by consolidating lava1 and the      
volcanic cones fall into a condition of 
extinction and decay4    ,the existence 

of heated materials at no great depth   
from the surface  is indicated by the   
outburst of gases and vapours1 the      
formation of  geysers1 mud-volcanoes1   
and ordinary thermal springs4 ,but as   
the  underlying rocks cool down1 the    
issuing jets of gas and vapour lose     
their high temperature and diminish in  
quantity1 the geysers and  mud-volcanoes
 become extinct1 and the thermal springs
 lose their  peculiar character or      
disappear1 and thus all manifestations  
of the  igneous energies in the district
 gradually die away4    ,sidenote3      
,,duration ,,of ,,volcanic ,,cycles4    
,such a cycle of changes probably       
requires many hundreds of thousands1  or
 even many millions1 of years for its   
accomplishment2 but by the  study of    
volcanoes in every stage of their growth
 and decline we are  able to reconstruct
 even the minutest details of their     
history4          ,,chapter ,,viii4     
,,the ,,distribution ,,of ,,volcanoes   
,,upon ,,the ,,surface ,,of ,,the       

,,globe4      ,it is not by any means an
 easy task to frame an estimate of the  
number  of volcanoes in the world4      
,volcanoes1 as we have seen1 vary       
greatly  in their dimensions--from vast 
mountain masses1 rising to a height  of 
nearly #be1jjj feet above the sea-level1
 to mere molehills2 the  smaller ones   
being in many cases subsidiary to       
larger1 and constituting  either        
parasitic cones on their flanks1 or     
'puys' around their bases4  ,volcanoes  
likewise exhibit every possible stage of
 development and  decay3 while some are 
in a state of chronic active eruption1  
others  are reduced to the condition of 
solfataras1 and others again have       
fallen into a more or less complete     
state of ruin through the action of     
denuding forces4    ,even if we confine 
our attention to the larger volcanoes1  
which merit  the name of 'mountains1'   
and such of these as we have reason to  
believe to be in a still active         
condition1 our difficulties will be     

diminished1 but not by any means        
removed4 ,volcanoes1 as we have seen1   
may sink into a dormant condition that  
may endure for hundreds or  even        
thousands of years1 and then burst forth
 into a state of renewed  activity2 and 
it is quite impossible1 in many cases1  
to distinguish  between the conditions  
of dormancy and extinction4 ,concerning 
certain  small areas in ,southern       
,europe1 ,western ,asia1 and ,northern  
,africa1  historical records1 more or   
less reliable1 extend back over periods 
of  several thousands of years2 but with
 regard to the greater part of the  rest
 of the world we have no information    
beyond a few hundred years1  and there  
are considerable areas which have been  
known only for far  shorter periods1    
while some are as yet quite unexplored4 
,in districts  almost wholly            
uninhabited1 or roamed over by nomadic  
tribes1 legend  and tradition constitute
 our only guides--and very unsafe ones  
they  are--in the attempt to determine  

what volcanoes have recently been in a  
condition of activity4    ,sidenote3    
,,number ,,of ,,active ,,volcanoes4     
,we shall1 however1 probably be within  
the limits of truth in stating  that the
 number of great habitual volcanic vents
 upon the globe1  which we have reason  
to believe are still in an active       
condition1 is  somewhere between #cjj   
and #cej4 ,most of these active volcanic
 vents  are marked by more or less      
considerable mountains1 composed of the 
materials ejected from them4 ,if we     
include the mountains which exhibit  the
 external conical form1 the crateral    
hollows1 and other features  of         
volcanoes1 but concerning the activity  
of which we have no record  or          
tradition1 the number will fall little1 
if anything1 short of  #a1jjj4 ,the     
mountains composed of volcanic          
materials1 but which have  lost through 
denudation the external form of         
volcanoes1 are still more  numerous4    
,the smaller temporary openings which   

are usually subordinate  to the habitual
 vents1 that have been active during the
 periods  covered by history and        
tradition1 must be numbered by thousands
 and  tens of thousands4 ,the still     
feebler manifestations of the volcanic  
forces--such as are exhibited in        
'stufas1' or steam-jets1 geysers1  or   
intermittent hot springs1 thermal and   
mineral waters1 fumaroles1  emitting    
various gases1 salses or spouting saline
 and muddy springs1  and mud            
volcanoes--may be reckoned by millions4 
,it is not improbable  that these less  
powerful manifestations of the volcanic 
forces1 to a  great extent make up in   
number what they want in individual     
energy2 and  the relief which they      
afford to the imprisoned activities     
within the  earth's crust may be        
scarcely less than that which results   
from the  occasional outbursts at the   
#cjj or #cej great habitual volcanic    
vents4    ,in taking a general survey of
 the volcanic phenomena of the globe1   

no fact comes out more strikingly than  
that of the very unequal  distribution1 
in different districts1 both of the     
great habitual  volcanic vents1 and of  
the minor exhibitions of subterranean   
energy4    ,sidenote3 ,,volcanoes ,,of  
,,the ,,continents4    ,thus1 on the    
whole of the continent of ,europe1 there
 is but one  habitual volcanic          
vent--that of ,vesuvius--and this is    
situated upon  the shores of the        
,mediterranean4 ,in the islands of the  
,mediterranean1  however1 there are no  
less than six volcanoes2 namely1        
,stromboli and  ,vulcano1 in the ,lipari
 ,islands2 ,etna1 in ,sicily2 ,graham's 
,isle1 a  submarine volcano1 off the    
,sicilian coast2 and ,santorin and      
,nisyros1 in  the gean ,sea4    ,the    
,african continent is at present known  
to contain about ten active             
volcanoes--four on the west coast1 and  
six on the east coast2 about ten  other 
active volcanoes occur on islands close 
to the ,african coasts4 ,in  ,asia1     

twenty-four active volcanoes are known1 
but no less than twelve  of these are   
situated in the peninsula of            
,kamtschatka4 ,no volcanoes are  known  
to exist in the ,australian continent4  
,the ,american continent contains a     
greater number of volcanoes than  the   
divisions of the ,old ,world4 ,there are
 twenty in ,north ,america1  twenty-five
 in ,central ,america1 and thirty-seven 
in ,south ,america4    ,thus1 taken     
altogether1 there are about one hundred 
and seventeen  volcanoes situated on the
 great continental lands of the globe1  
while  nearly twice as many occur upon  
the islands scattered over the various  
oceans4    ,upon examining further into 
the distribution of the continental     
volcanoes1 another very interesting fact
 presents itself4 ,the volcanoes  are in
 almost every case situated either close
 to the coasts of the  continent1 or at 
no great distance from them4 ,there are1
 indeed1 only  two exceptions to this   
rule4 ,in the great and almost wholly   

unexplored  table-land lying between    
,siberia and ,tibet four volcanoes are  
said to  exist1 and in the ,chinese     
province of ,mantchouria several others4
 ,more  reliable information is1        
however1 needed concerning these        
volcanoes1  situated1 unlike all others1
 at a great distance from the sea4      
,it is a remarkable circumstance that   
all the oceanic islands which  are not  
coral-reefs are composed of volcanic    
rocks2 and many of these  oceanic       
islands1 as well as others lying near   
the shores of the  continents1 contain  
active volcanoes4    ,through the midst 
of the ,atlantic ,ocean runs a ridge1   
which1 by the  soundings of the various 
exploring vessels sent out in recent    
years1  has been shown to divide the    
ocean longitudinally into two basins4   
,upon this great ridge1 and the spurs   
proceeding from it1 rise numerous       
mountainous masses1 which constitute the
 well-known ,atlantic islands  and      
groups of islands4 ,all of these are of 

volcanic origin1 and among  them are    
numerous active volcanoes4 ,the ,island 
of ,jan ,mayen contains  an active      
volcano1 while ,iceland contains        
thirteen1 and not improbably  more2 the 
,azores have six active volcanoes1 the  
,canaries three2 while  about eight     
volcanoes lie off the west coast of     
,africa4 ,in the ,west  ,indies there   
are six active volcanoes2 and three     
submarine volcanoes  have been recorded 
within the limits of the ,atlantic      
,ocean4 ,altogether1  no less than forty
 active volcanoes are situated upon the 
great  submarine ridges which traverse  
the ,atlantic longitudinally4           
,sidenote3 ,,volcanoes ,,on ,,the       
,,oceanic ,,islands4    ,but along the  
same line the number of extinct         
volcanoes is far greater1  and there are
 not wanting proofs that the volcanoes  
which are still  active are approaching 
the condition of extinction4 ,at a      
somewhat  earlier period of the earth's 
history the whole line of the present   

,atlantic ,ocean was in all probability 
traversed by a chain of volcanoes  on   
the very grandest scale2 but submergence
 has taken place1 and only a  few       
portions of this great mountain range   
now rise above the sea-level1  forming  
the isolated islands and island-groups  
of the ,atlantic4 ,here  and there among
 these a still active volcano exists4   
,but if the great medial chain of the   
,atlantic presents us with an  example  
of a chain of volcanic mountains verging
 on extinction1 we have  in the line of 
islands separating the ,pacific and     
,indian ,oceans an  example of a similar
 range of volcanic vents which are in a 
condition  of the greatest activity4 ,in
 the peninsula of ,kamtschatka there are
  twelve active volcanoes1 in the       
,aleutian ,islands thirty-one1 and in   
the peninsula of ,alaska three4 ,the    
chain of the ,kuriles contains at  least
 ten active volcanoes2 the ,japanese    
,islands and the islands lying  to the  
south of ,japan twenty-five4 ,the great 

group of islands lying  to the          
south-east of the ,asiatic continent is 
at the present time the  grandest focus 
of volcanic activity upon the globe4 ,no
 less than fifty  active volcanoes occur
 here4 ,farther south1 the same chain is
 probably  continued by the four active 
volcanoes of ,new ,guinea1 one or more  
submarine volcanoes1 and several vents  
in ,new ,britain1 the ,solomon  ,isles1 
and the ,new ,hebrides1 the three active
 volcanoes of ,new ,zealand1  and       
possibly by ,mount ,erebus and ,mount   
,terror in the ,antarctic region4       
,altogether1 no less than #aej active   
volcanoes exist in the chain of  islands
 which stretch from ,behring's ,straits 
down to the ,antarctic  circle2 and if  
we include the volcanoes on ,indian and 
,pacific islands  which appear to be    
situated on lines branching from this   
particular  band1 we shall not be wrong 
in the assertion that this great system 
of  volcanic mountains includes at least
 one half of the habitually active      

vents of the globe4    ,a third series  
of volcanoes starts from near the last  
in the  neighbourhood of ,behring's     
,straits1 and stretches along the whole 
western coast of the ,american          
continent4 ,in this great range there   
are  about eighty active volcanoes4     
,sidenote3 ,,linear ,,arrangement ,,of  
,,volcanoes4    ,in considering the     
facts connected with the distribution of
 volcanoes  upon the globe1 the one     
which1 by its striking character1 seems 
to  demand our attention in the first   
instance is that of the remarkable      
linear arrangement of volcanic vents4   
,we have already seen that small        
scoria-cones are often thrown up on the 
flanks1 or at the base1 of a  great     
volcanic mountain1 along lines which are
 manifestly lines of  fissure4 ,in the  
eruption of ,etna1 in #ahfe1 and again  
in that of #ahgd1  ,professor           
,silvestri1 of ,catania1 witnessed the  
actual opening of great  fissures on the
 north-east and north sides of the      

mountain3 and  along the bottom of these
 cracks the glowing lava was clearly    
visible  7fig4 #hd1 page #aid74 ,in the 
course of a few days1 there were thrown 
up a number of small scoria-cones along 
these lines of fissure--those  formed on
 the fissure of #ahfe being seven in    
number1 and those on the  fissure of    
#ahgd being no less than thirty-six in  
number4 ,precisely  familiar phenomena  
were witnessed upon the slopes of       
,vesuvius1 in #agfj1  when a fissure    
opened on the south side of the         
mountain1 and fifteen  scoria-cones1    
which are still visible1 were thrown up 
along it4    ,we have already considered
 the evidence pointing to the conclusion
 that  systems of volcanoes1 like that  
of the ,lipari ,islands1 are similarly  
ranged along lines of fissures1 and     
there is equally good ground for        
believing that the great linear bands of
 volcanoes1 which1 as we  have seen1    
stretch for thousands of miles1 have had
 their positions  determined by great   

lines of fissure in the earth's crust4  
,while1  however1 the smaller fissures1 
upon which rows of scoria-cones are     
thrown up1 seem to have been in many    
cases opened by a single effort  of the 
volcanic forces1 the enormous fissures1 
which traverse so large  a portion of   
the surface of the globe1 are doubtless 
the result of  numerous manifestations  
of energy extending over vast periods of
 time4    ,the greatest of these bands  
along which the volcanic forces are so  
powerfully exhibited at the present day1
 is the one which stretches  from near  
the ,arctic circle at ,behring's        
,straits to the ,antarctic  circle at   
,south ,victoria4 ,the line followed by 
this volcanic band1  which1 as we have  
seen1 includes more than one half of the
 active  volcanoes of the globe1 is a   
very sinuous one1 and it gives off      
numerous offshoots upon either side of  
it4 ,the great focus of this  intense   
volcanic action may be regarded as lying
 in the district  between the islands of

 ,borneo and ,new ,guinea4 ,from this   
centre there  radiate a number of great 
lines1 along which the volcanic forces  
are  exhibited in the most powerful     
manner4 ,the first of these extends     
northwards through the ,philippine      
,isles1 ,japan1 the ,kurile ,islands1   
and  ,kamtschatka1 giving off a branch  
to the east1 which passes through the   
,aleutian ,islands and the peninsula of 
,alaska4 ,this band1 along which  the   
volcanic forces are very powerfully     
active1 is continued towards  the       
south-east in the ,new ,britain1 the    
,solomon ,islands1 ,santa ,cruz1 the    
,new ,hebrides1 ,new ,zealand1 and      
,south ,victoria4 ,east and west from   
the  great central focus there proceed  
two principal branches4 ,the former  of 
these extends through the ,navigator    
,islands and ,friendly ,islands  as far 
as ,elizabeth ,islands4 ,the latter     
passes through ,java1 and then  turns   
north-westward through ,sumatra1 the    
,nicobar ,islands1 the ,andaman         

,islands up to the coast of ,burmah4    
,the great band which we have been      
describing exhibits the most  striking  
examples of volcanic activity to be     
found upon the globe4  ,besides the #aej
 or more volcanoes which are known to   
have been in a  state of activity during
 the historical period1 there are       
several  hundred very perfect volcanic  
cones1 many of which appear to have but 
recently become extinct1 if indeed1 they
 are not simply in a dormant  condition4
 ,for long distances these chains of    
volcanic cones are almost  continuous1  
and the only very considerable breaks in
 the series are  those between ,new     
,zealand and the ,new ,hebrides on the  
one hand1 and  between the former       
islands and ,south ,victoria on the     
other4    ,sidenote3 ,,great ,,volcanic 
,,bands ,,of ,,the ,,globe4    ,much    
less continuous1 but nevertheless very  
important1 is the great  band of        
volcanoes which extends along the       
western side of the great  ,american    

continent1 and contains1 with its       
branches1 nearly a hundred  active      
volcanoes4 ,on the north this great band
 is almost united with  the one we have 
already described by the chain of the   
,aleutian and  ,alaska volcanoes4 ,in   
,british ,columbia about the parallel of
 #fj ,n4  there exist a number of       
volcanic mountains1 one of which1 ,mount
 ,st4  ,elias1 is believed to be #ah1jjj
 feet in height1 and several of these   
have certainly been seen in a state of  
eruption4 ,farther south in the  part of
 the ,united ,states1 territories       
drained by the ,columbia ,river1  a     
number of grand volcanic mountains      
exist1 some of which are probably  still
 active1 for geysers and other          
manifestations of volcanic activity     
abound4 ,from the southern extremity of 
the peninsula of ,california  an almost 
continuous chain of volcanoes stretches 
through ,mexico and  ,guatemala1 and    
from this part of the volcanic band a   
branch is given  off which passes       

through the ,west ,indies1 and forms a  
connection with  the great volcanic band
 of the ,atlantic ,ocean4 ,in ,south    
,america the  line is continued by the  
active volcanoes of ,ecuador1 ,bolivia  
and  ,chili1 but at many intermediate   
points in the chain of the ,andes       
extinct volcanoes occur1 which to a     
great extent fill up the gaps  in the   
series4 ,a small offshoot to the        
westward passes through the  ,galapagos 
,islands4 ,the great band of volcanoes  
which stretches through  the ,american  
continent is second only in importance1 
and in the  activity of its vents1 to   
the band which divides the ,pacific from
 the  ,indian ,ocean4    ,the third     
volcanic band of the globe is that which
 traverses the  ,atlantic ,ocean from   
north to south4 ,this series of volcanic
 mountains  is much more broken and     
interrupted than the other two1 and a   
greater  proportion of its vents are    
extinct4 ,this chain1 as we shall show  
in a  future chapter1 attained its      

condition of maximum activity during the
  distant period of the ,miocene1 and   
now appears to be passing into a  state 
of gradual extinction4 ,beginning in the
 north with the volcanic  rocks of      
,greenland and ,bear ,island1 we pass   
southwards1 by way of ,jan  ,mayen1     
,iceland1 and the ,faroe ,islands1 to   
the ,hebrides and the north  of         
,ireland4 ,thence by way of the ,azores1
 the ,canaries and the ,cape de  ,verde 
,islands1 with some active vents1 we    
pass to the ruined volcanoes  of ,st4   
,paul1 ,fernando de ,noronha1           
,ascension1 ,st4 ,helena1 ,trinidad and 
,tristan d',acunha4 ,from this great    
,atlantic band two branches proceed  to 
the eastward1 one through ,central      
,europe1 where all the vents are  now   
extinct1 and the other through the      
,mediterranean to ,asia ,minor1  the    
great majority of the volcanoes along   
the latter line being now  extinct1     
though a few are still active4 ,the vol 
canoes on the eastern  coast of ,africa 

may be regarded as situated on another  
branch from this  ,atlantic volcanic    
band4 ,the number of active volcanoes on
 this ,atlantic  band and its branches1 
exclusive of those in the ,west ,indies1
 does not  exceed fifty4    ,sidenote3  
,,length ,,of ,,the ,,volcanic ,,bands4 
,from what has been said1 it will be    
seen that1 not only do the  volcanoes of
 the globe usually assume a linear      
arrangement1 but nearly  the whole of   
them can be shown to be thrown up along 
three well-marked  bands and the        
branches proceeding from them4 ,the     
first and most  important of these bands
 is nearly #aj1jjj miles in length1 and 
with its  branches contains more than   
#aej active volcanoes2 the second is    
#h1jjj  miles in length1 and includes   
about #ajj active volcanoes2 the third  
is  much more broken and interrupted1   
extends to a length of nearly #a1jjj    
miles1 and contains about #ej active    
vents4 ,the volcanoes of the eastern    
coast of ,africa1 with ,mauritius1      

,bourbon1 ,rodriguez1 and the vents     
along the line of the ,red ,sea1 may be 
regarded as forming a fourth and        
subordinate band4    ,thus we see that  
the surface of the globe is covered by a
 network  of volcanic bands1 all of     
which traverse it in sinuous lines with 
a  general north-and-south direction1   
giving off branches which often  run for
 hundreds of miles1 and sometimes appear
 to form a connection  between the great
 bands4    ,these four bands of volcanic
 vents1 running in a general            
north-and-south direction1 separate four
 unequal areas within which the         
exhibitions of volcanic activity are    
feeble or quite unknown4 ,the two       
grandest of the bands of volcanic       
activity1 with their branches1 form  an 
almost complete series encircling the   
largest of the oceans4    ,to this rule 
of the linear arrangement of the        
volcanic vents of the  globe and their  
accumulation along certain well-marked  
bands1 there are  two very striking     

exceptions1 which we must now proceed to
 notice4    ,in the very centre of the  
continent formed by ,europe and ,asia1  
the  largest unbroken land-mass of the  
globe1 there rises from the great       
central plateau the remarkable volcanoes
 of the ,thian ,shan ,range4  ,the      
existence of these volcanoes1 of which  
only obscure traditional  accounts had  
reached ,europe before the year #aheh1  
appears to be  completely established by
 the researches of the ,russian         
traveller  ,semenof4 ,three volcanic    
vents appear to exist in this region3   
the  active volcanoes of ,boschan and   
,turfan or ,hot-schen1 and the solfatara
  of ,urumtsi4 ,at a point situated     
about half-way between these three      
volcanoes and the sea1 another active   
vent1 that of ,ujung-,holdongi1 is  said
 to exist4 ,other volcanic phenomena    
have been stated to occur in  the great 
plateau of ,central ,asia1 but the      
existence of some at least  of these    
appears to rest on very doubtful        

evidence4 ,the only accounts  which we  
have of the eruptions of these ,thian   
,shan volcanoes are  contained in       
,chinese histories and treatises on     
geography2 and a great  service would be
 rendered to science could they be      
visited by some  competent explorer4    
,sidenote3 ,,exceptionally-,,situated   
,,volcanoes4    ,the second             
exceptionally-situated volcanic group is
 that of the  ,sandwich ,islands4 ,while
 the ,thian ,shan volcanoes rise in the 
centre of  the largest unbroken         
land-mass1 and stand on the edge of the 
loftiest  and greatest plateau in the   
world1 the volcanoes of the ,sandwich   
,islands rise almost in the centre of   
the largest ocean and from almost  the  
greatest depths in that ocean4 ,all     
round the ,sandwich ,islands the  sea   
has a depth of from #b1jjj to #c1jjj    
fathoms1 and the island-group           
culminates in several volcanic cones    
which rise to the height of nearly      
#ad1jjj feet above the sea-level4 ,the  

volcanoes of the ,sandwich ,islands  are
 unsurpassed in height and bulk by those
 of any other part of the  globe4       
,with the exception of the two isolated 
groups of the ,thian ,shan and  the     
,sandwich ,islands1 nearly all the      
active volcanoes of the globe  are      
situated near the limits which separate 
the great land- and  water-masses of the
 globe--that is to say1 they occur      
either on the  parts of continents not  
far removed from their coast-lines1 or  
on  islands in the ocean not very       
distant from the shores4    ,the fact of
 the general proximity of volcanoes to  
the sea1 is one which  has frequently   
been pointed out by geographers1 and may
 now be regarded  as being thoroughly   
established4 ,even the apparently       
anomalous case of  the ,thian ,shan     
volcanoes is susceptible of explanation 
if we remember  the fact1 now well      
ascertained by geological researches1   
that as  late certainly as ,pliocene    
times1 a great inland sea spread over   

the  districts where the ,caspian1 the  
,sea of ,aral1 and many other isolated  
lakes are now found4 ,upon the southern 
shore of this sea rose the  volcanoes of
 the ,thian ,shan1 some of which have   
not yet fallen into a  state of complete
 extinction4    ,but although the facts 
concerning the general proximity of     
volcanoes to  the ocean may be admitted 
to be thoroughly established1 yet       
inferences  are sometimes hastily drawn 
from these facts which the latter1 if   
fairly considered1 will not be found to 
warrant4 ,it is frequently  assumed that
 we may refer all the remarkable        
phenomena of volcanic  action to the    
penetration of sea-water to a mass of   
incandescent lava  in the earth's crust1
 and to the chemical or mechanical      
action which  would result from this    
meeting of sea-water and molten rock4   
,and this  conclusion is supposed to    
find support in the circumstance that   
many  of the gases and volatile         
substances emitted from volcanic vents  

are  such as would be produced by the   
decomposition of the various salts      
contained in sea-water4    ,this        
argument in favour of the production of 
volcanic outbursts by  the irruption of 
sea-water into subterranean reservoirs1 
involves1 as  ,mr4 ,scrope long ago     
pointed out1 a curious example of       
reasoning in a  circle4 ,it is assumed1 
on the one hand1 that the heaving       
subterranean  movements1 which give rise
 to the fissures by which steam and     
other  gases escape to the surface1 are 
the result of the passage of water  to  
heated masses in the earth's crust4     
,but1 on the other hand1 it is  supposed
 that it is the production of these     
fissures which leads to  the influx of  
water to the heated materials4 ,if it is
 the passage of  water through these    
fissures which produces the eruptions1  
it may be  fairly asked1 what is it that
 gives rise to the fissures8 ,and if1 on
  the other hand1 there exist           
subterranean forces competent to produce

  the fissures1 may they not also give  
rise to the eruptions through the       
openings which they have originated8    
,nor does the chemical argument  appear 
to rest upon any surer ground4 ,it is   
true that many of the  volatile         
substances emitted from volcanic vents  
are such as might be  produced by the   
decomposition of sea-water1 but1 upon   
the other hand1  there are not a few    
substances which cannot possibly be     
regarded as so  produced1 and1 all the  
materials may equally well be supposed  
to have  been originally imprisoned in  
the masses of subterranean lava4        
,sidenote3 ,,cause ,,of ,,proximity ,,of
 ,,volcanoes ,,to ,,sea4    ,the problem
 before us is this4 ,granting that it is
 proved that active  volcanoes are      
always in close proximity to the ocean1 
are we to explain  the fact by supposing
 that the agency of sea-water is        
necessary to  volcanic outbursts1 or by 
regarding the position of the           
coast-lines  as to some extent          

determined by the distribution of       
volcanic action  upon the surface of the
 globe8 ,the first supposition is the   
one which  perhaps most readily suggests
 itself1 but the latter1 as we shall    
hereafter show1 is one in favour of     
which not a few weighty arguments  may  
be advanced4    ,another problem which  
suggests itself in connection with the  
distribution of volcanoes is the        
following4 ,are the great depressed     
tracts which form the bottom of the     
oceans1 like the elevated tracts  which 
constitute the continents1 equally free 
from exhibitions of  volcanic energy8   
,when we remember the fact that the area
 of the ocean beds is two and           
three-quarter times as great as that of 
the continents1 it will be seen  how    
important this question of the existence
 of volcanoes at the bottom  of the     
ocean really is4    ,the fact that      
recent deep-sea soundings have shown the
 deepest parts  of the ocean to be      
everywhere covered with volcanic dbris  

is by  no means conclusive upon this    
question2 for1 as we have seen1 the     
ejections of sub-aerial volcanoes are by
 the wind and waves distributed  over   
every part of the earth's surface4      
,sidenote3 ,,submarine ,,eruptions4     
,submarine volcanic outbursts have      
occurred in many parts of the  globe1   
but it may well be doubted whether any  
such outburst has ever  commenced at the
 bottom of a deep ocean1 and has        
succeeded in building  up a volcanic    
cone reaching to the surface4 ,most1 if 
not all1 of the  recorded submarine     
outbursts have occurred in the midst of 
volcanic  districts1 and the volcanic   
cones have been built up in water of no 
great depth4 ,indeed1 when it is        
remembered that the pressure of each    
#a1jjj fathoms of water is equivalent to
 a weight of more than one ton  on every
 square inch of the ocean-bottom1 it is 
difficult to imagine  the ordinary      
explosive action of volcanic vents      
taking place at abysmal  depths4 ,if1   

however1 fissures were opened in the    
beds of the ocean1  quiet outwellings of
 lava might possibly occur4    ,the     
solution of this problem of the probable
 existence of volcanic  outbursts on the
 floor of the ocean can only be hoped   
for from the  researches of the         
geologist4 ,the small specimens of the  
ocean-beds  brought up by deep-sea      
sounding-lines1 taken at wide distances 
apart1  and including but a few inches  
from the surface1 can certainly afford  
but little information upon the         
question4 ,but the geologist has the    
opportunity of studying the sea-bottoms 
of various geological periods  which    
have been upheaved and are now exposed  
to his view4 ,it was at  one time       
supposed by geologists that in the      
so-called 'trap-rocks' we  have great   
lava-sheets which must have been piled  
upon one another1  without explosive    
action4 ,but the more accurate          
researches of recent  years have shown  
that between the layers of 'trap-rock1' 

in every part  of the globe1 traces of  
terrestrial surfaces and freshwater     
deposits  are found2 and the supposed   
proofs of the absence of explosive      
action  break down no less signally upon
 re-examination2 for the loose1         
scoriaceous materials would either be   
removed by denudation1 or  converted    
into hard and solid rocks by the        
infilling of their vesicles  and        
air-cavities with crystalline minerals4 
,it is not possible1 among  the         
representatives of former geological    
periods1 to point to any rocks  that can
 be fairly regarded as having issued    
from great submarine  fissures1 and it  
is therefore fair to conclude that no   
such great  outbursts of the volcanic   
forces take plane at the present day on 
the  deep ocean-floors4    ,in          
connection with the question of the     
relation between the position of  the   
volcanic bands of the globe and the     
areas covered by the ocean1 we  may     
mention a fact which deep-sea soundings 

appear to indicate1 namely1  that the   
deepest holes in the ocean-floor are    
situated in volcanic  areas4 ,near      
,japan1 the soundings of the ,u4,s4 ship
 ',tuscarora' showed  that at two points
 the depth exceeded #d1jjj fathoms2 and 
the deepest  sounding obtained by       
,h4,m4,s4 ',challenger1' amounting to   
#d1ege fathoms1  was taken in the voyage
 from ,new ,gruinea to ,japan1 in the   
neighbourhood  of the ,ladrone ,islands4
 ,depths nearly as great were found in  
the  soundings carried on in the        
neighbourhood of the volcanic group of  
the  ,west ,indian ,islands4 ,it must be
 remembered1 however1 that at present   
our knowledge of the depths of the      
abysmal portions of the ocean is  very  
limited4 ,a few lines of soundings1     
often taken at great distances  apart1  
are all we have to guide us to any      
conclusions concerning the  floors of   
the great oceans1 and between these     
lines are enormous areas  which still   
remain altogether unexplored4 ,it may be

 wise1 therefore1 to  suspend our       
judgment upon such questions till more  
numerous facts have  been obtained4     
,sidenote3 ,,relations ,,to             
,,mountain-,,chains4    ,another fact   
concerning the distribution of volcanoes
 which is worthy  of remark is their    
relation to the great mountain-ranges of
 the globe4    ,many of the grandest    
mountain-chains have bands of volcanoes 
lying parallel to them4 ,this is        
stinkingly exhibited by the great       
mountain-masses which lie on the western
 side of the ,american  continent4 ,the 
,rocky ,mountains and the ,andes consist
 of folded and  crumpled masses of      
altered strata which1 by the action of  
denuding  forces1 have been carved into 
series of ridges and summits4 ,at many  
points1 however1 along the sides of     
these great chains1 we find that        
fissures have been opened and lines of  
volcanoes formed1 from which  enormous  
quantities of lava have flowed and      
covered great tracts of  country4 ,at   

some parts of the chain1 however1 the   
volcanoes are of such  height and       
dimensions as to overlook and dwarf the 
mountain-ranges by  the side of which   
they lie4 ,some of the volcanoes lying  
parallel to the  great ,american axis   
appear to be quite extinct1 while others
 are in  full activity4    ,in the      
,eastern continent we find still more   
striking examples of  the parallelism   
between great mountain-chains and the   
lands along  which volcanic activity is 
exhibited4 ,stretching in a more or less
  continuous chain from east to west1   
through ,europe and ,asia1 we find  the 
mountain-masses known in different parts
 of their course as the  ,pyrenees1 the 
,alps1 the ,balkan1 the ,caucasus1 which
 form the axis  of the ,eastern         
continent4 ,these chains consist of     
numerous parallel  ridges1 and give off 
branches on either side of them4 ,they  
are  continued to the eastward by the   
,hindoo ,koosh and the ,himalaya1 with  
the four parallel ranges that cross the 

great ,central-,asian plateau4  ,now1 on
 either side of this grand axial system 
of mountains1 we find  a great parallel 
band of volcanoes4 ,the northern        
volcanic band is  constituted by the    
eruptive rocks of the ,auvergne1 the    
,eifel1 the  ,siebengebirge1 ,central   
,germany1 ,bohemia1 ,hungary1 and       
,transylvania1  few1 if any1 of the     
vents along this northern band being    
still active4  ,the remarkable volcanoes
 of the ,thian ,shan range and of       
,mantchouria may  not improbably be     
regarded as a continuation of the same  
great series4    ,the southern band of  
volcanoes1 lying parallel to the great  
mountain  axis of the ,old ,world1 also 
consists for the most part of extinct   
volcanoes1 but includes not a few vents 
which are still active4 ,in  this band  
we include the extinct volcanoes of     
,spain and ,sardinia1 the  numerous     
extinct and active vents of the ,italian
 peninsula and islands1  and those of   
the gean ,sea and ,asia ,minor4 ,we may1

 perhaps1 consider  the scattered       
volcanoes of ,arabia and the northern   
part of the ,indian  ,ocean as a        
continuation of the same series4 ,both  
of these bands may  be regarded as      
offshoots from the great mid-,atlantic  
volcanic chain1  and the condition of   
the vents1 both in the principal band   
and its  offshoots1 is such as to       
indicate that they form parts of a      
system  which is gradually sinking into 
a state of complete extinction4         
,there are some other volcanic bands    
which exhibit a similar parallelism     
with mountain chains2 but1 on the other 
hand1 there are some volcanoes  between 
which and the nearest mountain axes no  
such connection can be  traced4         
,sidenote3 ,,relation ,,to ,,areas ,,of 
,,upheaval4    ,there is yet one other  
fact concerning the mode of distribution
 of  volcanoes upon the surface of the  
globe1 to which we must allude4 ,it  was
 first established by ,mr4 ,darwin as   
one of the conclusions derived  from the

 valuable series of observations made by
 him during the voyage  of ,h4,m4,s4    
',beagle1' and relates to the position  
of active volcanoes  with respect to the
 portions of the earth's crust which are
 undergoing  upheaval or subsidence4    
,from the relative position of the      
different kinds of coral-reefs1 and  the
 fact that reef-forming corals cannot   
live at a depth of more than  twenty    
fathoms beneath the sea-level1 or above 
tide-mark1 we are led to  the conclusion
 that certain areas of the earth's      
surface are undergoing  slow elevation1 
while other parts are as gradually      
subsiding4 ,this  conclusion is         
confirmed by the occurrence of raised   
beaches1 which  are sometimes found at  
heights of hundreds1 or even thousands1 
of  feet above the sea-level1 and of    
submerged forests1 which are not        
unfrequently found beneath the waters of
 the ocean4    ,by a study of the       
evidences presented by coral-reefs1     
raised beaches1  submerged forests1 and 

other phenomena of a similar kind1 it   
can be  shown that certain wide areas of
 the land and of the ocean-floor are  at
 the present time in a state of         
subsidence1 while other equally  large  
areas are being upheaved4 ,and the      
observations of the geologist  prove    
that similar upward and downward        
movements of portions of the  earth's   
crust have been going on through all    
geological times4 ,now1  as ,mr4 ,darwin
 has so well shown in his work on       
',coral-,reefs1' if we  trace upon a map
 the areas of the earth's surface which 
are undergoing  upheaval and subsidence 
respectively1 we shall find that nearly 
all the  active volcanoes of the globe  
are situated upon rising areas1 and that
  volcanic phenomena are conspicuously  
absent from those parts of the  earth's 
crust which can be proved at the present
 day to be undergoing  depression4      
,,chapter ,,ix4    ,,volcanic ,,action  
,,at ,,different ,,periods ,,of ,,the   
,,earth',s ,,history4      ,it is only  

in comparatively recent times that the  
important doctrine of  geological       
continuity has come to be generally     
accepted1 as furnishing  us with a      
complete and satisfactory explanation of
 the mode of origin  of the features of 
our globe4 ,the great forces1 which are 
ever at  work producing modifications in
 those features1 operate so silently    
and slowly1 though withal so surely1    
that without the closest and  most      
attentive observation their effects may 
be easily overlooked2  while1 on the    
other hand1 there are so many phenomena 
upon our globe  which seem at first     
sight to bear testimony to the action of
 sudden  and catastrophic forces1 very  
different to any which appear to be at  
present at work1 that the tendency to   
account for all past changes by  these  
violent actions is a very strong one4   
,in spite of this tendency1  however1   
the real potency of the forces now at   
work upon the earth's  crust has        
gradually made its way to recognition1  

and the capability of  these forces1    
when their effects are accumulated      
through sufficiently  long periods of   
time1 to bring about the grandest       
changes1 is now  almost universally     
admitted4 ,the modern science of geology
 is based  upon the principle that the  
history of the formation and development
  of the earth's surface-features1 and  
of the organisms upon it1 has  been     
continuous during enormous periods of   
time1 and that in the study  of the     
operations taking place upon the earth  
at the present day1 we  may find the    
true key to the changes which have      
occurred during former  periods4    ,in 
no branch of geological science has the 
doctrine of continuity  had to encounter
 so much opposition and misconception as
 in that  which relates to the volcanic 
phenomena of the globe4 ,for a long time
  students of rocks utterly failed to   
recognise any relation between the      
materials which have been ejected from  
active volcanic vents and those  which  

have been formed by similar agencies at 
earlier periods of the  earth's history4
 ,and what was far worse1 the subject   
became removed  from the sphere of      
practical scientific inquiry to that of 
theological  controversy1 those who     
maintained the volcanic origin of some  
of the  older rocks being branded as the
 worst of heretics4    ,sidenote3       
,,controversy ,,concerning ,,origin ,,of
 ,,basalt4    ,with the theological     
aspects of the great controversy        
concerning the  origin of basalt and    
similar rocks--a controversy which was  
carried  on with such violence and      
acrimony during the latter half of the  
eighteenth century--we have here nothing
 to do4 ,but it may not be              
uninstructive to notice the causes of   
the strange misconceptions which  for so
 long a period stood in the way of the  
acceptance of rational  views upon the  
subject4    ,at this period but little  
had been done in studying the chemical  
characters of aqueous and igneous       

rock-masses respectively2 and while1  on
 the one hand1 the close similarity in  
chemical composition between  the       
ancient basalts and many modern lavas   
was not recognised1 the  marked         
distinction between the composition of  
such materials and most  aqueous        
sediments remained1 on the other hand1  
equally unknown4 ,nor  had anything been
 yet accomplished in the direction of   
the study of  rock-masses by the aid of 
the microscope4 ,hence there could be no
  appeal to those numerous structural   
peculiarities that at once enable  us to
 distinguish the most crystalline       
aqueous rocks from the materials  of    
igneous origin4    ,on the other hand1  
there undoubtedly exist rocks of a black
 colour  and crystalline structure1     
sometimes presenting a striking         
similarity  in general appearance to the
 basalts1 which contain fossils and are 
undoubtedly of aqueous origin4 ,thus on 
the shore near ,portrush1 in the  ,north
 of ,ireland1 and in the skerries which 

lie off that coast1 there  occur great  
rock-masses1 some of which undoubtedly  
agree with basalt in  all their         
characters1 while others are            
dark-coloured and crystalline1  and are 
frequently crowded with ,ammonites and  
other fossils4 ,we now  know that the   
explanation of these facts is as        
follows4 ,near where  the town of       
,portrush is now situated1 a volcanic   
vent was opened in  ,miocene times      
through rocks of ,lias shale4 ,from this
 igneous centre1  sheets and dykes of   
basaltic lava were given off1 and in    
consequence  of their contact with these
 masses of lava1 the ,lias shales were  
baked  and altered1 and assumed a       
crystalline character1 though the traces
 of  the fossils contained in them were 
not altogether obliterated4 ,in the     
last century the methods which had been 
devised for the discrimination  of rocks
 were so imperfect that no distinction  
was recognised between  the true basalt 
and the altered shale1 and specimens of 

the latter  containing ,ammonites found 
their way to almost every museum in     
,europe1 and were used as illustrations 
of the 'origin of basalt by  aqueous    
precipitation4'    ,another source of   
the widely-spread error which prevailed 
concerning  the origin of basalt1 was   
the failure to recognise the nature of  
the alterations which take place in the 
character of rock-masses in  consequence
 of the passage through them1 during    
enormous periods of  time1 of water     
containing carbonic acid and other      
active chemical  agents4 ,the casual    
observer does not recognise the         
resemblance which  exists between       
certain ornamental marbles and the loose
 accumulations  of shells and corals    
which form many sea-beaches2 but close  
examination  shows that the former      
consist of the same materials as the    
latter1  bound together by a crystalline
 infilling of carbonate of lime1 which  
has been deposited in all the cavities  
and interstices of the mass4 ,in  the   

same way1 as we have already seen1 the  
vesicles and interstices  of heaps of   
scori may1 by the percolation of water  
through the mass1  become so filled with
 various crystalline substances1 that   
its original  characters are entirely   
masked4    ,but the progress of chemical
 and microscopic research has           
effectually  removed these sources of   
error4 ,many rocks of aqueous origin1   
formerly  confounded with the basalts1  
have now been relegated to their proper 
places among the different classes of   
rocks2 while1 on the other  hand1 it has
 been shown that the chemical and       
physical differences  between the       
ancient basalts and the modern basic    
lavas are slight  and accidental1 and   
their resemblances are of the closest   
and most  fundamental character4        
,sidenote3 ,,volcanic ,,origin ,,of     
',,trap ,,rocks4'    ,the notion of the 
aqueous origin of basalt1 which was so  
long  maintained by the school of       
,werner1 has now been entirely          

abandoned1  and the so-called           
'trap-rocks' are at the present day     
recognised as  being as truly volcanic  
in their origin as the lavas of ,etna   
and  ,vesuvius4    ,there is1 however1 a
 vestige of this doctrine of ,werner1   
which still  maintains its ground with  
obstinate persistence4 ,many geologists 
in  ,germany who admit that volcanic    
phenomena1 similar to those which are   
going on at the present day1 must have  
occurred during the ,tertiary and  the  
later ,secondary periods1 nevertheless  
insist that among the earlier  records  
of the world's history we find no       
evidence whatever of such  volcanic     
action having taken place4 ,by the      
geologists who hold these  views it is  
asserted that while the granites and    
other plutonic rocks  were formed during
 the earlier periods of the world's     
history1 true  volcanic products are    
only known in connection with the       
sediment of the  later geological       
periods4    ,some geologists have gone  

farther even than this1 and asserted    
that  each of the great geological      
periods is characterised by the nature  
of the igneous ejections which have     
taken place in it4 ,they declare  that  
granite was formed only during the      
earliest geological periods1  and that  
at later dates the gabbros1 diabases1   
porphyries1 dolerites  and basalts1     
successively made their appearance1 and 
finally that the  modern lavas were     
poured out4    ,a little consideration  
will suffice to convince us that these  
conclusions are not based upon any good 
evidence4 ,the plutonic rocks1  as we   
have already seen1 exhibit sufficient   
proofs in their highly  crystalline     
character1 and in their cavities        
containing water1  liquefied carbonic   
acid1 and other volatile substances1    
that they must  have been formed by the 
very slow consolidation of igneous      
materials  under enormous pressure4     
,such pressures1 it is evident1 could   
only  exist at great depths beneath the 

earth's surface4 ,mr4 ,sorby and  others
 have endeavoured to calculate what was 
the actual thickness of  rock under     
which certain granites must have been   
formed1 by measuring  the amount of     
contraction in the liquids which have   
been imprisoned  in the crystals of     
these rocks4 ,the conclusions arrived at
 are of a  sufficiently startling       
character4 ,it is inferred that the     
granites  which have been thus examined 
must have consolidated at depths varying
  from #cj1jjj to #hj1jjj feet beneath  
the earth's surface4 ,it is true  that  
in arriving at these results certain    
assumptions have to be made1  and to    
these exception may be taken1 but the   
general conclusion that  granitic rocks 
could only have been formed under such  
high pressures as  exist at great depths
 beneath the surface1 appears to be one 
which is  not open to reasonable doubt4 
,if1 then1 granites and similar rocks   
were formed at the depth of some  miles1
 it is evident that they can only have  

made their appearance at  the surface by
 the removal of the vast thickness of   
overlying rocks2  and the sole agency   
which we know of that is capable of     
effecting the  removal of such enormous 
quantities of rock-materials1 is        
denudation4  ,but the agents of         
denudation--rain and frost1 rivers and  
glaciers1 and  sea-waves--though        
producing grand results1 yet work       
exceeding slowly2  and almost           
inconceivably long periods of time must 
have elapsed before  masses of rock     
several miles in thickness could have   
been removed1 and  the subjacent        
granites and other highly crystalline   
rocks have been  exposed at the surface4
    ,sidenote3 ,,ancient ,,and ,,modern 
,,volcanic ,,rocks4    ,it is an        
admitted fact that among the older      
geological formations1 we  much more    
frequently find intrusions of granitic  
rocks than in the case  of younger ones4
 ,it is equally true that among the     
sediments formed  during the most recent

 geological periods1 no true granitic   
rocks have  been detected4 ,but if1 as  
we insist is the case1 granitic rocks   
can  only be formed at a great depth    
from the surface1 the acts we have      
described are only just what we might   
expect to present themselves  under the 
circumstances4 ,the older a mass of     
granitic rock1 the greater  chance there
 is that the denuding forces operating  
upon the overlying  masses1 will have   
had an opportunity of so far removing   
the latter  as to expose the underlying 
crystalline rocks at the surface4 ,and1 
on the other hand1 the younger          
crystalline rocks are still1 for the    
most part1 buried under such enormous   
thicknesses of superincumbent  materials
 that it is hopeless for us to search   
for them4 ,nevertheless1  it does       
occasionally happen that1 where the work
 of denudation has been  exceptionally  
rapid in its action1 such crystalline   
rocks formed during  a comparatively    
recent geological period1 are exposed at

 the surface4  ,this is the case in the 
,western ,isles of ,scotland and in the 
,pyrenees1  where masses of granite and 
other highly crystalline rocks are found
  which were evidently formed during the
 ,tertiary period4    ,the granites     
which were formed in ,tertiary times    
present no essential  points of         
difference from those which had their   
origin during the  earlier periods of   
the earth's history4 ,the former1 like  
the latter1  consist of a mass of       
crystals with no imperfectly crystalline
 base or  groundmass between them2 and  
these crystals include numerous cavities
  containing liquids4    ,between the   
granites and the quartz-felsites every  
possible  gradation may be found1 so    
that it is impossible to say where the  
one  group ends and the other begins2   
indeed1 many of the rocks called        
'granite-porphyries' have about equal   
claims to be placed in either  class4   
,nor is the distinction between the     
quartz-felsites and rhyolites  any more 

strongly marked than that between the   
former class of rocks  and the granites2
 some of the more crystalline rhyolites 
of ,hungary  being quite                
undistinguishable1 in their chemical    
composition1 their  mineralogical       
constitution1 and their microscopic     
characters1 from  the quartz-felsites4  
,the more crystalline rhyolites are in  
turn found  passing by insensible       
gradations into the glassy varieties and
 finally  into obsidian4    ,sidenote3  
,,relations ,,between ,,granite ,,and   
,,pumice4    ,a piece of granite and a  
piece of pumice may at first sight      
appear to  present so many points of    
difference1 that it would seem quite    
futile  to attempt to discover any      
connection between them4 ,yet1 if we    
analyse  the two substances1 we may find
 that in ultimate chemical composition  
they are absolutely identical4 ,there is
 nothing irrational1 therefore1  in the 
conclusion that the same materials under
 different conditions  may assume either

 the characters of granite on the one   
hand1 or of  pumice on the other2 the   
former being consolidated under         
circumstances  in which the chemical and
 crystalline forces have had the freest 
play  and have used up the whole of the 
materials to form crystallised          
minerals1 while the latter has cooled   
down and solidified rapidly at  the     
surface1 in such a way that only        
incipient crystallisation has  occurred1
 and the glassy mass has been reduced to
 a frothy condition  by the escape of   
steam-bubbles from its midst ,this      
conclusion receives  the strongest      
support from the fact that examples of  
every stage of  the change1 between the 
glassy condition of pumice and the      
crystalline  condition of granite1 may  
be detected among the materials of which
 the  globe is built up4    ,there is   
still another class of facts which may  
be adduced in  support of the same      
conclusion4 ,many lavas1 as we have     
seen1 contain  crystals of much larger  

dimensions than those constituting the  
mass  of the rock1 which is then said to
 be 'porphyritic' in structure4  ,the   
porphyritically embedded crystals1 when 
carefully examined1 are  often seen to  
be broken and injured1 and to exhibit   
rounded edges1  with other indications  
of having undergone transport4 ,when    
examined  microscopically1 too1 they    
often present the cavities containing   
liquids which distinguish the crystals  
of plutonic rocks4 ,all the  facts      
connected with these porphyritic lavas  
point to the conclusion  that while the 
crystals in their groundmass have       
separated from the  liquefied materials 
near the surface1 the large embedded    
crystal1 have  been floated up from     
great depths within the earth's crust1  
where they  had been originally formed4 
,sidenote3 ,,granitic ,,representatives 
,,of ,,other ,,lavas4    ,the careful   
consideration of all the facts of the   
case leads to the  conclusion that where
 pumice1 obsidian1 and rhyolite are now 

being  ejected at the surface1 the      
materials which form these substances   
are1 at various depths in the earth's   
interior1 slowly consolidating  in the  
form of quartz-felsite1 granite-porphyry
 and granite4 ,it may  be that we can   
nowhere point to the example of a mass  
of rock which  can be traced from       
subterranean regions to the surface1 and
 is1 under  such conditions1 actually   
seen to pass from the dense and         
crystalline  condition of granite to the
 vesicular and glassy form of pumice2   
but great granitic masses often exhibit 
a more coarsely crystalline  condition  
in their interior1 and the offshoots and
 dykes which they  give off not         
infrequently assume the form of         
quartz-felsite2 while1  on the other    
hand1 the more slowly consolidated rocks
 found in the  interior of some rhyolite
 masses are not distinguishable in any  
way  from some of the true              
quartz-felsites4    ,that which is true 
of the lavas of acid composition is     

equally true  of the lavas of           
intermediate and basic character4 ,the  
andesites1  the trachytes1 the          
phonolites1 and the basalts have all    
their exact  representatives among the  
plutonic rocks1 and these have a        
perfectly  crystalline or granitic      
structure4 ,the plutonic and the        
volcanic  representatives of each of    
these groups are identical in their     
chemical  composition1 and numerous     
intermediate gradations can be found    
between  the most completely granitic   
and the most perfectly vitreous or      
glassy  types4 ,in illustration of this 
fact1 we may again refer to the series  
of microscopic sections of rocks given  
in the frontispiece4    ,another        
objection to the conclusion that the    
volcanic products of  earlier periods of
 the earth's history were identical in  
character with  those which are being   
ejected at the present day is based on  
the fact  of the supposed non-existence 
of the scoriaceous and glassy materials 

which abound in the neighbourhood of the
 active volcanic vents4 ,where1  it is  
asked1 do we find among the older rocks 
of the globe the heaps of  lapilli1     
dust1 and scori1 with the glassy and    
pumiceous rocks that now  occur so      
abundantly in all volcanic districts8   
,in reply to this objection1 we may     
point out that these accumulations  of  
loose materials are of such a nature as 
to be capable of easy  removal by       
denuding agents1 and that as they are   
formed upon the land  they will1 if not 
already washed away by the action of    
rain1 floods1  rivers1 c41 run great    
risk of having their materials          
distributed1  when the land sinks       
beneath the waters of the ocean and the 
surface  is covered by new deposits4    
,with respect to the glassy rocks it    
must  be remembered that the action of  
water1 containing carbonic acid and     
other substances1 in percolating through
 such masses has a tendency  to set up  
crystalline action1 and these glassy    

rocks easily undergo  'devitrification'2
 it would therefore be illogical for us 
to expect  glassy rock-masses to retain 
their vitreous character through long   
geological periods1 during which they   
have been subjected to the action  of   
water and acid gases4    ,but careful   
observation has shown that the          
scoriaceous and vitreous  rocks are by  
no means absent among the igneous       
materials ejected during  earlier       
periods of the earth's history4 ,their  
comparative infrequency  is easily      
accounted for when we remember1 in the  
first place1 the ease  with which such  
materials would be removed by denuding  
forces1 and in  the second place1 the   
tendency of the action of percolating   
water to  destroy their characteristic  
features1 by filling up their vesicles  
with crystalline products and by        
effecting devitrification in their      
mass4    ,sidenote3 ,,similarity ,,of   
,,ancient ,,and ,,recent ,,lavas4    ,if
 we go back to the very oldest known    

rock-masses of the globe1 those  which  
are found underlying the fossiliferous  
,cambrian strata1 we find  abundant     
evidence that volcanic action took place
 during the period  in which these      
materials were being accumulated4 ,thus1
 in the ,wrekin1  as ,mr4 ,allport has  
so well shown1 we find clear proofs that
 before  the long-distant period of the 
,cambrian1 there existed volcanoes      
which ejected scori1 lapilli1 and       
volcanic dust1 and also gave rise  to   
streams of lava exhibiting the          
characteristic structures found in      
glassy rocks4 ,in these rocks1 which    
have undergone a curious alteration  or 
devitrification1 we still find all those
 peculiar structures--the  sphrulitic1  
the perlitic1 and the banded--so common 
in the rhyolites  of ,hungary1 with     
which rocks the ,wrekin lavas1 in their 
chemical  composition1 precisely agree4 
,prof4 ,bonney1 too1 has shown that the 
rocks of ,charnwood ,forest1 which are  
also probably of pre-,cambrian age1     

contain great quantities of altered     
volcanic agglomerates1 tuffs1 and       
ashes4 ,i have found the sphrulitic1    
perlitic1 and banded structures         
exhibited by ,british lavas of the      
,cambrian1 ,silurian1 ,devonian and     
,carboniferous periods1 as well as in   
those of ,tertiary age2 and in          
connection with these different lavas we
 find vast accumulations1  sometimes    
thousands of feet in thickness1 of      
volcanic agglomerates and  tuffs which  
have undergone great alteration4    ,all
 these facts point to one               
conclusion--namely1 that during all past
  geological periods1 materials similar 
to those which are now being  extruded  
from volcanic vents were poured out on  
the earth's surface  by analogous       
agencies4 ,if we could trace the        
lava-streams of the  present day down to
 the great subterranean reservoirs from 
which their  materials have been        
derived1 we should doubtless find that  
at gradually  increasing depths1 where  

the pressure would be greater and the   
escape  of heat from the mass slower1   
the rocky materials would by degrees    
assume more and more crystalline        
characters4 ,we should thus find        
obsidian or rhyolite insensibly passing 
into quartz-felsite and finally  into   
granite2 trachyte passing into          
orthoclase-porphyry and syenite2  and   
basalt passing into dolerite1           
augite-porphyry1 and gabbro4    ,on the 
other hand1 if we could replace the     
great masses of stratified  rocks which 
must once have overlain the granites1   
syenites1 diorites1  and gabbros1 we    
should find that1 as we approached the  
original  surface1 these igneous        
materials would gradually lose their    
crystalline  characters1 and when they  
were poured out at the surface would    
take the  forms of rhyolite1 trachyte1  
andesite1 and basalt--all of which might
  occasionally assume the glassy forms  
known as obsidian or tachylyte4         
,sidenote3 ,,altered ,,forms ,,of       

,,ancient ,,lavas4    ,but while we     
insist on the essential points of       
similarity between  the lavas poured out
 upon the surface of the earth during   
earlier  geological periods and those   
which are being extruded at the present 
day1 we must not forget that by the     
action of percolating water and  acid   
gases1 the mineral constitution1 the    
structure1 and sometimes  even the      
chemical composition of these ancient   
lavas may undergo  a vast amount of     
change4 ,in not a few cases these       
changes in the  characters of a lava may
 be carried so far that the altered rock
 bears  but little resemblance to the   
lava from which it was formed1 and it   
may  be found desirable to give it a new
 name4 ,among the rocks of aqueous      
origin we find similar differences in   
the materials deposited at  different   
geological periods4 ,clay1 shale and    
clay-slate have the same  composition1  
and the two latter are evidently only   
altered forms of the  first mentioned1  

yet so great is the difference in their 
characters  that it is not only         
allowable1 but desirable1 to give them  
distinctive  names4    ,in the same way1
 among the deposits of the earlier      
geological periods  we find rocks which 
were doubtless originally basalts1 but  
in which  great alterations have been   
produced by the percolation of water    
through the mass4 ,the original rock has
 consisted of crystals of  felspar1     
augite1 olivine1 and magnetite          
distributed through a glassy  base4 ,but
 the chemical action of water and       
carbonic acid may have  affected all the
 ingredients of the rock4 ,the outward  
form of the  felspar crystals may be    
retained while their substance is       
changed to  kaolinite1 various zeolites1
 and other minerals2 the olivine maybe  
altered to serpentine and other         
analogous minerals2 the magnetite       
changed to hydrous peroxide of iron2 the
 augite may be changed to  uralite or   
hornblende2 and the surrounding glassy  

mass more or  less devitrified and      
decomposed4 ,the hard1 dense1 and black 
rock  known as basalt has under these   
circumstances become a much softer1     
earthy-looking mass of a reddish-brown  
tint1 and its difference from  basalt is
 so marked that geologists have agreed  
to call it by another  name1 that of    
'melaphyre4' ,even in their ultimate    
chemical compositions  the 'melaphyres' 
differ to some extent from the basalts1 
for some of  the materials of the latter
 may have been removed in solution1 and 
water1 oxygen1 and carbonic acid have   
been introduced to combine with  the    
remaining ingredients4    ,but if we    
carefully study1 by the aid of the      
microscope1 a large series  of basalts  
and melaphyres1 we shall find that many 
rocks of the former  class show the     
first incipient traces of those changes 
which would  reduce them to the latter  
class4 ,indeed1 it is quite easy to form
 a  perfect series from quite unaltered 
basalts to the most completely  changed 

melaphyres4 ,hence we are justified in  
concluding that all the  melaphyres were
 originally basalts1 just as we infer   
that all oaks were  once acorns4    ,now
 changes1 similar to those which we have
 seen to take place in  the case of     
basaltic lavas1 are exhibited by the    
lavas of every  other class1 which have 
been exposed to the influence of the    
same  agencies1--namely1 the passage of 
water and acid gases4 ,but inasmuch as  
the minerals composing the basic lavas  
are for the most part much more  easily 
affected by such agencies than are the  
minerals of acid lavas1  the ancient    
basic rocks are usually found in a much 
more highly altered  condition than are 
the acid rocks of equivalent age4       
,sidenote3 ,,names ,,given ,,to         
,,altered ,,lavas4    ,we thus see that 
each of the classes of modern lavas has 
its  representative in earlier          
geological periods1 in the form of rocks
  which have evidently been derived from
 these lavas1 through alterations       

effected by the agency of water and     
acid-gases that have permeated  their   
mass4 ,thus1 while the basalts are      
represented among the ancient           
geological formation by the melaphyres1 
the andesites are represented  by the   
porphyrites1 and the trachytes and      
rhyolites by different  varieties of    
felstones4 ,and1 as we can form perfect 
series illustrating  the gradual change 
from basalt to melaphyre1 so we can     
arrange other  series demonstrating the 
passage of andesites into porphyrites1  
and of  trachytes and rhyolites into    
felsites4    ,it must be remembered1    
however1 that these changes do not take 
place  in anything like determinate     
periods of time4 ,occasionally we may   
find lavas of ancient date which have   
undergone surprisingly little           
alteration1 and in other cases there    
occur lavas belonging to a              
comparatively recent period which       
exhibit very marked signs of change4    
,the alteration of the lavas and other  

igneous rocks does not1 however1  stop  
with the production of the melaphyres1  
porphyrites1 and felstones4  ,by the    
further action of the water and carbonic
 acid of the atmosphere1  the basic     
lavas are reduced to the soft earthy    
mass known as 'wacke1'  and the         
intermediate and acid lavas to the      
similar material known as  'claystone4' 
,as the passage of water and carbonic   
acid gas through  these rock-masses goes
 on1 they are eventually resolved into  
two  portions1 one of which is insoluble
 in water and the other is soluble4     
,the insoluble portion consists         
principally of quartz1 the crystals  of 
which are almost unattacked by water and
 carbonic acid1 and the  hydrated       
silicate of alumina4 ,all the sands and 
clays1 which together  make up more than
 nine-tenths of the stratified rocks of 
the globe1  are doubtless derived1      
either directly or indirectly1 from     
these  insoluble materials separated    
during the decomposition of volcanic and

  plutonic rocks4 ,the soluble          
materials1 which consist of the         
carbonates1  sulphates and chlorides of 
lime1 magnesia1 soda1 potash1 and iron1 
give rise to the formation of the       
limestones1 gypsum1 rock-salt1          
ironstones1 and other stratified masses 
of the earth's crust4 ,we thus  see how 
the igneous materials of the globe1 by  
their decomposition1  famish the        
materials for the stratified            
rock-masses4 ,the relations of  the     
different plutonic and volcanic rocks to
 one another and to the  materials which
 are derived from them are illustrated  
in the following  table4    ,sidenote3  
,,relations ,,of ,,altered ,,to         
,,unaltered ,,lavas4                    
,unaltered   ,altered   ,decomposed     
,plutonic ,rocks                lavas   
lavas      ,rocks      ,granite         
,quartz-felsite        ,rhyolite and    
7'quartz-porphyry'7   ,obsidian         
,felstone                               
,syenite  ,orthoclase-porphyry          

,trachyte                  ,claystones  
,diorite  ,hornblende-porphyry          
,andesite       ,porphyrite             
,miascite ,liebnerite porphyry          
,phonolite          8         --        
,gabbro   ,augite-porphyry and   ,basalt
         ,melaphyre    ,wacke           
,dolerite                 ,some         
petrographers1 indeed1 have maintained  
the principle that rocks  belonging to  
widely separated geological periods1    
even when they  exhibit no essential    
points of difference1 should            
nevertheless be  called by distinct     
names4 ,but such a system of            
classification is  calculated rather to 
hinder than to advance the cause of     
science4 ,if  the palontologist were to 
adopt the same principle and give       
distinct  names to the same fossil1 when
 it was found to occur in two different 
geological formations1 we can easily    
understand what confusion would  be     
occasioned1 and how the comparison of   
the fauna and flora of the  different   

formations would be thereby rendered    
impossible4 ,but the  naturalist1 in his
 diagnosis of a species1 wisely confines
 himself  to the structure and          
affinities of the organism before him2  
and in  the same way the petrographer1  
in giving a name to a rock1 ought  to be
 guided only by his studies of its      
chemical composition1 its  mineralogical
 constitution1 and its structure1       
putting altogether  out of view its     
geographical distribution and geological
 age4 ,only  by strict attention to this
 principle can we hope to arrive at such
  comparisons of the rocks of different 
areas and different periods1 as  may    
serve as the basis for safe inductions4 
,before leaving this question of the    
relation which exists between the       
igneous rocks of different ages1 it may 
be well to notice several facts  that   
have been relied upon1 as proving that  
the several geological  periods are     
distinguished by characteristic igneous 
products4    ,it has frequently been    

asserted that the acid igneous rocks are
 present  in much greater quantities in 
connection with the older geological    
formations than axe the basic2 while1 on
 the other hand1 the basic  igneous     
rocks are said to have been extruded in 
greater abundance in  the more recent   
geological periods4 ,but in considering 
this question it  must not be forgotten 
that1 as a general rule1 the basic rocks
 undergo  decomposition and             
disintegration far more rapidly than do 
the acid  rocks4 ,in consequence of this
 circumstance the chance of our finding 
their recognisable representatives among
 the older formations1 is much  less in 
the case of the former class of rocks   
than in the latter4 ,as a  matter of    
fact1 however1 we do find great masses  
of gabbro1 diabase1  and melaphyre      
associated even with the oldest         
geological formations1  while trachytes 
and rhyolites abound in many volcanic   
districts where  active vents exist at  
the present day4 ,upon a general review 

of the  subject1 it may well be doubted 
whether the supposed preponderance of   
acid igneous materials in the earlier   
periods of the earth's history1  and of 
basic igneous materials during the later
 periods1 rests on any  substantial     
basis of observation4    ,sidenote3     
,,augitic ,,and ,,hornblendic ,,rocks4  
,another difference which has frequently
 been relied upon1 as  distinguishing   
the older igneous rocks from those of   
more recent date1  is the supposed fact 
that the former are characterised by the
 presence  of hornblende1 the latter by 
the presence of augite4 ,it may be      
admitted  that this distinction is a    
real one1 but its significance and value
 are  greatly diminished when we        
remember the relations which exist      
between  the two minerals in question4  
,hornblende and augite are interesting  
examples of a dimorphous substance2 in  
chemical composition they are           
identical1 or rather they are liable to 
variation between the same  limits1 but 

in their crystalline forms and optical  
characters they  differ from one        
another4 ,it has been proved that       
hornblende is the  stable1 and augite   
the unstable condition of the substance 
in question4  ,if hornblende be fused   
and allowed to cool1 it crystallises in 
the form  of augite4 ,on the other hand1
 augite-crystals in rocks of ancient    
date  are found undergoing gradual      
change and passing into hornblende4 ,the
  mineral uralite has the outward form  
of augite1 but the cleavage and  optical
 properties of hornblende2 and there are
 not wanting many facts  pointing to the
 conclusion that rocks which now contain
 hornblende were  originally augitic    
masses1 in which the unstable mineral in
 their  midst has been gradually        
converted into the stable one4    ,there
 are1 however1 two minerals which up to 
the present time have  been found in    
association only with the older and     
newer rock-masses  respectively4 ,these 
are muscovite1 or the white form of     

mica1 which  occurs in so many granites1
 but has not yet been discovered in any 
modern representative of that rock2 and 
leucite1 which is not yet known  in     
rocks of older date than the ,tertiary4 
,when we remember that muscovite would  
appear to be a product of  deep-seated  
igneous action1 and is only found in    
rock-masses that have  been formed under
 such conditions1 we shall be the less  
surprised at  its non-occurrence in     
rocks of recent date1 especially if we  
bear in  mind the fact that very few of 
the younger granitic rocks have as yet  
been exposed at the surface by          
denudation4    ,with respect to leucite1
 on the other hand1 it must be          
remembered that  it is a very unstable  
mineral which appears to be easily      
changed into  felspar4 ,it is by no     
means improbable1 therefore1 that some  
ancient  igneous rocks which now contain
 felspar were originally leucitic rocks4
    ,to the view that the action of     
volcanic forces upon the globe during   

past geological times was similar in    
kind to that which we now observe  going
 on around us1 still another objection  
has been raised4 ,it has  been asserted 
that some of the deposits of igneous    
rock associated  with the older         
geological formations are of such a     
nature that they  could not possibly    
have been accumulated around volcanic   
vents of the  kind which we see in      
operation around us4    ,sidenote3      
,,volcanic ,,origin ,,of ,,ancient      
,,igneous ,,rocks4    ,mr4 ,mallet has  
declared that the igneous products of   
the ,palozoic  period differ            
fundamentally in character from those   
materials formed  by volcanic action    
during the later ,secondary and the     
,tertiary  periods4 ,upon what          
observations these generalisations are  
based he  has given us no information1  
and the enormous mass of facts which    
have been collected in recent years     
concerning the structure of the  lavas  
and fragmental volcanic deposits of the 

pre-,cambrian1 ,cambrian1  ,silurian1   
,devonian and ,carboniferous periods1   
all point to a directly  opposite       
conclusion4 ,the more carefully we carry
 on our investigations  concerning these
 ancient lavas1 by the aid of chemical  
analysis and  microscopic study1 the    
more are we convinced of the essential  
identity  of the ancient and modern     
volcanic rocks1 both in their           
composition  and their minute structure4
 ,of great masses of dust produced by   
crushing1 such as ,mr4 ,mallet has      
supposed to have been formed during  the
 earlier geological periods1 there is   
not the smallest evidence2  but we      
everywhere find proofs1 when the rocks  
are minutely examined1  of the vesicular
 structure so characteristic of         
materials produced by  explosive        
volcanic action4    ,it has frequently  
been asserted that in the great         
districts covered by  basaltic lavas    
which we find in the ,rocky ,mountains  
of ,north ,america1  in the ,deccan of  

,india1 in ,abyssinia1 and even in the  
,western ,isles of  ,scotland1 we have  
proofs of the occurrence1 during earlier
 geological  periods1 of volcanic action
 very different in character from that  
which at present takes place on our     
globe4 ,it has been asserted that  the  
phenomena observed in these districts   
can only be accounted for by  supposing 
that great fissures have opened in their
 midst1 from which  lavas have issued in
 enormous floods unaccompanied by the   
ordinary  explosive phenomena of        
volcanoes4    ,it must be remembered1   
however1 that none of the districts in  
question  have been subjected to careful
 and systematic examination with a view 
to the discovery of the vents from which
 these masses of lava have  issued1 with
 the exception of that which occurs in  
our own islands4 ,in  this case1 in     
which superficial observers have spoken 
of the district  as being covered with  
horizontal lava-sheets piled upon one   
another to  the depth of #c1jjj feet1   

careful study of the rock-masses has    
shown  that the accumulations of basalt 
really consist of a great number of     
lava-currents which have issued at      
successive epochs covering enormous     
periods of time4 ,during the intervals  
between the emission of these           
successive lava-currents the surfaces of
 the older ones have been  decomposed1  
and formed soils upon which forests have
 grown up2 they  have been eroded by    
streams1 the valleys so formed being    
filled with  gravels2 and lakes have    
been originated on their surfaces in    
which  various accumulations have taken 
place4    ,sidenote3 ,,truly-,,volcanic 
,,origin ,,of ,,lava ,,plateaux4    ,it 
has been demonstrated1 moreover1 that   
the basal-wrecks of no less  than five  
volcanic mountains1 each of which must  
have rivalled ,etna in  its proportions1
 existed within this area1 and the      
connection of the  lava-currents1 which 
have deluged the surrounding tracts1    
with these  great volcanoes has been    

clearly proved4 ,it is probable that    
when  more careful and systematic       
researches are carried on in the other  
districts1 in which widely-spread sheets
 of basaltic rocks exist1  similar      
volcanic vents will be discovered4 ,it  
must also be remembered  that if such a 
country as ,iceland were subjected to   
long-continued  denudation1 the mountain
 peaks and cones of loose materials     
would be  worn away1 the whole island   
being thus reduced to a series of       
plateaux  composed of lava-sheets1 the  
connection of which with the crystalline
  materials filling the great volcanic  
vents1 a superficial observer  might    
altogether fail to recognise4    ,but   
even where we cannot trace the former   
existence of great volcanic  mountains1 
like those which once rose in the       
,hebrides1 it would  nevertheless be    
very rash to conclude that the vast     
plateaux of  lava-rock must have been   
formed as gigantic floods unaccompanied 
by  ordinary volcanic action4 ,mr4      

,darwin has pointed out that in crossing
  districts covered by lava1 he was     
frequently only able to determine  the  
limits of the different currents of     
which it was made up1 by an  examination
 of the age of the trees and the nature 
of the vegetation  which had sprung up  
on them4 ,and everyone who has travelled
 much in  volcanic districts can confirm
 this observation2 what appears at first
  sight to be a great continuous sheet  
of lava proves upon more careful        
observation to be composed of a great   
number of distinctly different          
lava-currents1 which have succeeded one 
another at longer or shorter  intervals4
    ,we must remember1 too1 how various 
in kind are the volcanic  manifestations
 which present themselves under         
different circumstances4  ,sometimes the
 amount of explosive action at a        
volcanic vent is very  great1 and only  
fragmental ejections take place1        
composed of the frothy  scum of the lava
 produced by the escape of gases and    

vapours from its  midst4 ,but in other  
cases the amount of explosive action may
 be small1  and great volumes of igneous
 materials may issue as lava-streams4   
,in  such cases1 only small scori-cones 
would be formed around the vents1  and  
one half of such cones is commonly swept
 away by the efflux of the              
lava-currents1 while the remainder may  
be easily removed by denuding  action or
 be buried under the lava-currents      
issuing from other vents  in the        
neighbourhood4 ,thus it may easily come 
to pass that what a  superficial        
observer takes for an enormous mass of  
basaltic lava poured  out from a great  
fissure at a single effort1 may prove   
upon careful  observation to be made up 
of innumerable lava-currents1 each of   
which  is of moderate dimensions2 and it
 may further be found that these        
lava-currents1 instead of being the     
product of a single paroxysmal  effort  
from one great fissure1 have been       
accumulated by numerous small  outbursts

 taking place at wide intervals1 from a 
great number of minor  orifices4        
,sidenote3 ,,shifting ,,of ,,volcanic   
,,action ,,in ,,different ,,areas4      
,having then considered the arguments   
which have been adduced in support  of  
the view that the volcanic phenomena of 
former geological periods  differ from  
those which are still occurring upon the
 globe1 we may  proceed to state the    
general conclusions which have been     
drawn from the  study of the volcanic   
rocks of the different geological       
periods4    ,from a survey of the       
volcanic rocks of different ages1 we are
 led to  the interesting and important  
conclusion that the scene of volcanic   
action has been continually shifting to 
fresh areas at different  periods of the
 earth's history4 ,we find repeated     
proofs that the  volcanic energy has    
made its appearance at a certain part of
 the  earth's crust1 has gradually      
increased in intensity to a maximum1 and
  then as slowly declined4 ,but as these

 manifestations have died away  at one  
part of the earth's surface1 they have  
gradually made their  appearance at     
another4 ,in every district which has   
been examined1 we  find abundant proofs 
that volcanic energy has been developed 
at certain  periods1 has disappeared    
during longer or shorter periods1 and   
then  reappeared in the same area4 ,and 
on the other hand1 we find that there   
is no past geological period in which we
 have not abundant evidence  that       
volcanic outbursts took place at some   
portion of the earth's  surface4    ,to 
take the case of our own islands for    
example4 ,we know that during  the      
pre-,cambrian periods volcanic outbursts
 occurred1 traces of which  are found   
both in ,north and ,south ,wales1 in the
 ,wrekin ,chain in  ,shropshire1 in     
,charnwood ,forest1 and in parts of     
,scotland and ,ireland4    ,in          
,cambro-,silurian times we have abundant
 proofs1 both in ,north ,wales  and the 
,lake district1 that volcanic action on 

the very grandest  scale was taking     
place during the ,arenig and the older  
portion of  the ,llandeilo periods1 and 
again during the deposition of the ,bala
  or ,caradoc beds4 ,the lavas1 tuffs1  
and volcanic agglomerates ejected       
during these two periods have built up  
masses of rock many thousands of  feet  
in thickness4 ,snowdon and ,cader ,idris
 among the ,welsh mountains1  and some  
of the higher summits of the ,lake      
district1 have been carved  by          
denudation from the vast piles of       
volcanic materials ejected during  these
 periods4    ,in ,devonian or           
,old-,red-,sandstone times1 volcanic    
activity was renewed  with fresh        
violence upon that part of the earth's  
surface now occupied  by the ,british   
,islands4 ,along the line which now     
forms the ,grampians  there rose a      
series of volcanoes of the very grandest
 dimensions4 ,ben  ,nevis1 and many     
others among the higher ,scotch         
mountains1 have been  carved by         

denudation from the hard masses of      
granite1 quartz-felsite1  and other     
plutonic rocks which formed the central 
cores of these  ancient volcanic piles4 
,the remains of the great lava-sheets1  
and of  the masses of volcanic          
agglomerate ejected from these grand    
,devonian  volcanoes1 make up           
hill-ranges of no mean altitude1 like   
the ,sidlaws1  the ,ochils1 and the     
,pentlands4    ,sidenote3 ,,ancient     
,,british ,,volcanoes4    ,the volcanic 
action of the ,devonian period was      
prolonged into  ,carboniferous times1   
but was then evidently diminishing      
gradually in  violence4 ,instead of     
great central volcanoes1 such as existed
 in the  earlier period1 we find        
innumerable small vents which threw out 
tuffs1  agglomerates and lavas1 and were
 scattered over the districts lying     
around the bases of the now extinct     
,devonian volcanoes4 ,in the central    
valley of ,scotland and in many parts of
 ,england1 we find abundant  proofs of  

the existence of these small and        
scattered volcanic vents  during        
,carboniferous times4 ,the well-known   
hill of ,arthur's ,seat1 which          
overlooks the city of ,edinburgh1 and   
many castle-crowned crags of the  ,forth
 and ,clyde valleys1 are the worn and   
denuded relics of these small           
volcanoes4 ,there are some indications  
which point to the conclusion  that the 
volcanic action of the ,newer ,palozoic 
epoch had not entirely  died out in     
,permian times1 but the evidence upon   
this point is not  altogether clear and 
satisfactory4    ,during nearly the     
whole of the ,secondary or ,mesozoic    
periods the  volcanic forces remained   
dormant in the area of the ,british     
,isles4  ,some small volcanic outbursts1
 however1 appear to have occurred in    
,triassic times in ,devonshire4 ,but in 
other areas1 such as the ,tyrol1        
,south-eastern ,europe and ,western     
,america1 the ,triassic1 ,jurassic1 and 
,cretaceous periods were marked by grand

 manifestations of volcanic  activity4  
,the volcanic forces which had during   
the long ,mesozoic periods deserted  our
 part of the earth's surface1 appear to 
have returned to it in  full rigour in  
the ,tertiary epoch4 ,in the            
,newer-,palozoic periods  the direction 
of the great volcanic band which        
traversed our islands  appears to have  
been from north-east to south-west2 but 
in ,tertiary  times a new set of        
fissures were opened running from north 
to south4  ,there is evidence that      
during the ,eocene or ,nummulitic       
period1 the  first indications of the   
subterranean forces having gathered     
strength  below the district were       
afforded by the issue of calcareous and 
siliceous springs1 and soon fissures    
were opened which emitted scori1  tuffs1
 and lavas4 ,the intensity of the       
volcanic action gradually  increased    
till it attained its maximum in the     
,miocene period1 when  a great chain of 
volcanic mountains stretched north and  

south along  the line of the ,inner     
,hebrides1 the north-east of ,ireland1  
and the  sea which separates ,great     
,britain from ,ireland4 ,the            
basal-wrecks of a  number of these      
volcanoes can be traced in the islands  
of ,skye1 ,mull1  ,rum1 and parts of the
 adjoining mainland4 ,we have already   
seen that  along this great band of     
volcanic action1 which traverses the    
,atlantic  ,ocean from north to south1 a
 number of active vents still exist1    
though  their energy is now far less    
intense than was the case in former     
times4  ,the only vestiges of the action
 of these now declining volcanic forces1
  at present found in our islands1 are  
the hot springs of ,bath and a few      
other warm and mineral springs2 but in  
connection with this subject it  must be
 remembered that our country            
occasionally participates in great      
earthquake-vibrations1 like that which  
destroyed ,lisbon in the year  #agei4   
,sidenote3 ,,ancient ,,volcanoes ,,in   

,,other ,,districts4    ,if we were to  
study any other part of the earth's     
surface1 we should  arrive at precisely 
the same conclusion as those to which we
 have  been conducted by our examination
 of the ,british ,islands--namely1  that
 during past geological times the       
subterranean forces had made  themselves
 felt in the area1 had gradually        
attained a maximum1 and then  as        
gradually declined1 passing through all 
those varied cycles which we  have      
described in a former chapter4 ,and we  
should also find that these  periods of 
volcanic activity alternated with other 
periods of complete  quiescence which   
were of longer or shorter duration4 ,but
 on comparing  two different districts1 
we should discover that what was a      
period of  volcanic activity in the one 
was a period of repose in the other1 and
  vice vers4    ,from these facts       
geologists have been led to the         
conclusion which we  have already       
enunciated--namely1 that the            

subterranean forces are in a  state of  
continual flux over the surface of the  
globe4 ,at one point of  the earth's    
crust these forces gradually gather such
 energy as to rend  asunder the         
superincumbent rock-masses and make     
themselves manifest  at the surface in  
the series of phenomena characteristic  
of volcanic  action4 ,but after a longer
 or shorter interval of time--an        
interval  which must probably be        
measured by millions of years--the      
volcanic  forces die out in that area to
 make their appearance in another4      
,hence1 although we may not be able to  
prove the fact by any  mathematical     
demonstration1 a strong presumption is  
raised in favour  of the view that the  
subterranean energy in the earth's crust
 is a  constant quantity1 and that the  
only variations which take place are in 
the locality of its manifestation4      
,upon this question whether the amount  
of this subterranean energy  within the 
earth's crust is at the present time    

increasing1 stationary1  or declining1  
we are not altogether destitute of      
evidence4 ,there are  some              
considerations connected with certain   
astronomical hypotheses1 to  which we   
shall hereafter have to refer1 that     
might lead us to entertain  the view    
that the subterranean activity was once 
far greater than it  is at present1 and 
that during the long periods of the     
earth's past  history it has been slowly
 and gradually declining4 ,and those who
  examine the vast masses of igneous    
materials which have been poured  out   
from volcanic vents during the earlier  
periods of the earth's  history may be  
inclined1 at first sight1 to point to   
them as affording  conclusive proof of  
this gradual decline4    ,sidenote3     
,,supposed ,,decline ,,of ,,volcanic    
,,action4    ,but a more careful study  
of the rocks in question will probably  
cause  a geologist to pause before      
jumping to such a conclusion4 ,if we    
look  at the vast masses of volcanic    

materials erupted in ,miocene times in  
our own island and in ,ireland1 for     
example1 we might be led to imagine     
that we have the indications of a       
veritable ',reign of ,fire1' and that   
the evidence points to a condition of   
things very different indeed  from that 
which prevails at the present day4 ,but 
in arriving at such  a conclusion we    
should be neglecting a most important   
consideration1  the disregard of which  
has been the fertile parent of many     
geological  errors4 ,many independent   
lines of evidence all point to the      
inference  that these volcanic ejections
 are not the result of one violent      
effort1  but are the product of numerous
 small outbreaks which have been        
scattered over enormous periods of time4
    ,when we examine with due care the  
lavas1 tuffs1 and other volcanic        
ejections which constitute such         
mountain-masses as those of the         
,hebrides1 of the ,auvergne1 and of     
,hungary1 we find clear proofs  that the

 ancient ,miocene volcanoes of these    
districts were clothed  with luxuriant  
forests1 through which wild animals     
roamed in the  greatest abundance4 ,the 
intervals between the ejections of      
successive  lava-streams were often so  
great1 that soils were formed on the    
mountain-slope1 and streams cut deep    
ravines and valleys in them4    ,the    
island of ,java is situated near the    
very heart of what is at the  present   
day the most active volcanic centre on  
the face of the globe1  yet vegetable   
and animal life flourish luxuriantly    
there1 and the  island is one of the    
richest and most fertile spots upon the 
face of  the globe4 ,not all the terrors
 of occasional volcanic outbreaks will  
ever drive the ,neapolitan vine-dressers
 from the fertile slopes of  ,vesuvius1 
for its periods of repose are long1 and 
its eruptions are of  short duration4   
,these considerations lead the geologist
 to conclude that the evidence  afforded
 by the ancient volcanic rocks is clear 

and positive in support  of the view    
that the manifestations of the          
subterranean forces in the  past agree  
precisely in their nature and in their  
products with those  taking place around
 us at the present time4 ,on the        
question of great  secular changes      
having occurred in the amount of        
volcanic energy in  past geological     
periods1 the evidence must be pronounced
 negative1 or  at the best doubtful4    
,but even if the geologist confesses    
himself unable to establish the  fact of
 any decline in the subterranean        
energies during the vast  periods of    
which he takes cognisance1 it must be   
remembered that such  decline may really
 be going on2 for vast as was the       
duration of the  geological epochs1 they
 probably constitute but a fraction of  
those far  grander periods which are    
required by the speculations of the     
physical  astronomer4          ,,chapter
 ,x4    ,,the ,,part ,,played ,,by      
,,volcanoes ,,in ,,the ,,economy ,,of   

,,nature4      ,the first impression    
which is produced upon the mind1 when   
the  phenomena of volcanic action are   
studied1 is that here we have           
exhibitions of destructive violence the 
effects of which must be  entirely      
mischievous and disastrous to the living
 beings occupying the  earth's surface4 
,a little consideration will convince   
us1 however1 that  the grand and        
terrible character of the displays of   
volcanic energy  have given rise to     
exaggerated notions concerning their    
destructive  effects4 ,the fact that    
districts situated over the most        
powerful  volcanic foci1 like ,java and 
,japan1 are luxuriant in their          
productions1  and thickly inhabited1 may
 well lead us to pause ere we condemn   
volcanic action as productive only of   
mischief to the living beings  on the   
earth's surface4 ,the actual slopes of  
,vesuvius and ,etna1 and  many other    
active volcanoes1 are abundantly clothed
 with vineyards and  forests and are    

thickly studded with populous villages4 
,as a matter of fact1 the actual amount 
of damage to life and property  which is
 effected by volcanic eruptions is      
small4 ,usually1 the  inhabitants of the
 district have sufficient warning to    
enable them  to escape with their lives 
and to carry away their most valuable   
possessions4 ,and though fertile tracts 
are covered by loose dust and  ashes1 or
 by lava- and mud-currents1 yet the     
sterility thus produced  is generally of
 short duration1 for by their           
decomposition volcanic  materials give  
rise to the formation of the richest and
 most productive  soils4                
,earthquakes1 as we have already seen1  
are far more destructive in  their      
effects than are volcanoes4 ,houses and 
villages1 nay even entire  cities1 are1 
by vibrations of portions of the earth's
 crust1 reduced to  heaps of ruins1 and 
famines and pestilences too frequently  
follow1 as  the consequence of the      
disorganisation of our social systems by

 these  terrible catastrophes4    ,it   
may well be doubted1 however1 whether   
the annual average of  destruction to   
life and property caused by all kinds of
 subterranean  action1 exceeds that     
produced either by floods or by         
hurricanes4 ,yet  we know that the      
circulation of water and air over our   
globe are  beneficial and necessary     
operations1 and that the mischief       
occasionally  wrought by the moving     
bodies of water and air is quite        
insignificant  compared with the good   
which they effect4    ,in the same way1 
we shall be able to show that the       
subterranean  energies are necessary to 
the continued existence of our globe as 
a place fitted for the habitation of    
living beings1 and that the  mischievous
 and destructive effects of these       
energies bear but a small  and          
insignificant proportion to the         
beneficial results with which they  must
 be credited4    ,sidenote3 ,,levelling 
,,action ,,of ,,denuding ,,forces4      

,we have had frequent occasion in the   
preceding pages to refer to the         
work--slow but sure1 silent but         
effective--wrought by the action of  the
 denuding forces ever operating upon the
 surface of our globe4 ,the  waters     
condensing from the atmosphere and      
falling upon the land in  the form of   
rain1 snow1 or hail1 are charged with   
small quantities of  dissolved gases1   
and these waters penetrating among the  
rock-masses  of which the earth's crust 
is composed1 give rise to various       
chemical actions of which we have       
already noticed such remarkable         
illustrations in studying the ancient   
volcanic products of our globe4  ,by    
this action the hardest and most solid  
rock-masses are reduced  to a state of  
complete disintegration1 certain of     
their ingredients  undergoing           
decomposition1 and the cementing        
materials which hold  their particles   
together being removed in a state of    
solution4 ,in the  higher regions of the

 atmosphere this work of                
rock-disintegration  proceeds with the  
greatest rapidity2 for there the        
chemical action is  reinforced by the   
powerful mechanical action of freezing  
water4 ,on  high mountain-peaks the work
 of breaking up rock-masses goes on at  
the  most rapid rate1 and every craggy  
pinnacle is swathed by the heaps  of    
fragments which have fallen from it4    
,the ,alpine traveller justly  dreads   
the continual fusillade of falling      
rock-fragments which is  kept up by the 
ever-active power of the frost in these 
higher regions  of the atmosphere2 and  
fears lest the vibrations of his        
footsteps  should loosen1 from their    
position of precarious rest1 the rapidly
  accumulating piles of detritus4 ,no   
mountain-peak attains to any very  great
 elevation above the earth's surface1   
for the higher we rise in  the          
atmosphere the greater is the range of  
temperature and the more  destructive   
are the effects of the atmospheric      

water4 ,the moon1 which  is a much      
smaller planet than our earth1 has      
mountains of far greater  elevation2 but
 the moon possesses neither an          
atmosphere nor moisture on  its surface1
 to produce those levelling effects     
which we see everywhere  going on around
 us upon the earth4    ,the             
disintegrated materials1 produced by    
chemical and mechanical  actions of the 
atmospheric waters upon rock-masses1 are
 by floods1  rivers1 and glaciers1      
gradually transported from higher to    
lower  levels2 and sooner or later every
 fragment1 when it has once been        
separated from a mountain-top1 must     
reach the ocean1 where these  materials 
are accumulated and arranged to form new
 rocks4    ,over every part of the      
earth's surface these three grand       
operations of  the disintegration of old
 rock-masses1 the transport of the      
materials  so produced to lower levels1 
and the accumulation of these materials 
to form new rocks1 is continually going 

on4 ,it is by the varied action  of     
these denuding agents upon rocks of     
unequal hardness1 occupying  different  
positions in relation to one another1   
that all the external  features of      
hills1 and plains1 and mountains owe    
their origin4    ,it is a fact1 which is
 capable of mathematical demonstration1 
that by  the action of these denuding   
forces the surface of all the lands of  
the  globe is being gradually but surely
 lowered2 and this takes place at  such 
a rate that in a few millions of years  
the whole of the existing  continents   
must be washed away and their materials 
distributed over the  beds of the       
oceans4    ,sidenote3 ,,necessity ,,for 
,,compensating ,,agencies4    ,it is    
evident that there exists some agency by
 which this levelling  action of the    
denuding forces of the globe is         
compensated2 and a little  consideration
 will show that such compensating agency
 is found in the  subterranean forces   
ever at work within the earth's crust4  

,the effects  of these subterranean     
forces which most powerfully arrest our 
attention  are volcanic outbursts and   
earthquake shocks1 but a careful study  
of  the subject proves that these are by
 no means the most important of the     
results of the action of such forces4   
,exact observation has proved that      
almost every part of the earth's surface
 is either rising or falling1  and the  
striking and destructive phenomena of   
volcanoes and earthquakes  probably bear
 only the same relation to those grand  
and useful  actions of the subterranean 
forces1 which floods do to the system of
  circulating waters1 and hurricanes to 
the system of moving air-currents4      
,if we ride in a well-appointed carriage
 with good springs1 upon  a railway     
which is in excellent order1 the        
movement is almost  imperceptible to us2
 and the rate of speed may be increased 
indefinitely1 without making itself     
apparent to our senses4 ,the  smallest  
impediment to the evenness of the       

movement--such as that  produced by a   
small object placed upon the rails--at  
once makes itself  felt by a violent jar
 and vibration4 ,how perfectly          
insensible we may  be of the grandest   
and most rapid movements is taught us by
 the facts  demonstrated by the         
astronomer4 ,by the earth's daily       
rotation1 we are  borne along at a rate 
which in some places amounts to over    
#a1jjj miles  an hour2 and by its annual
 revolution we are every hour           
transported  through a distance of      
#gj1jjj miles2 yet concerning the fact  
and  direction of these movements we are
 wholly unconscious4    ,in the case    
both of the railway train and of our    
planet1 we can only  establish the      
reality of the movement1 and its        
direction and rate1 by  means of        
observations upon external objects1     
which appear to us to  have a movement  
in the opposite direction4 ,in the same 
way we can only  establish the fact of  
the movement of portions of the earth's 

crust  by noticing the changing         
positions of parts of the earth's       
surface in  relation to the constant    
level of the ocean4 ,when this is done  
we find  abundant proof that while some 
parts of the earth's crust are rising1  
others are as undoubtedly undergoing    
depression4    ,sidenote3 ,,potency ,,of
 ,,the ,,subterranean ,,forces4    ,we  
shall be able to form some idea of the  
vastness of the effects  produced by the
 subterranean forces1 by a very simple  
consideration4  ,it is certain that     
during the enormous periods of time of  
which the  records have been discovered 
by the geologist1 there have always been
  continents and oceans upon the earth's
 surface1 just as at present1  and it is
 almost equally certain that the        
proportions of the earth's  surface     
occupied by land and water respectively1
 have not varied very  widely from those
 which now prevail4 ,but1 at the same   
time1 it is an  equally well-established
 bet that the denuding forces ever at   

work  upon the earth's surface would    
have been competent to the removal  of  
existing continents many times over1 in 
the vast periods covered  by geological 
records4 ,hence we are driven to        
conclude that the  subterranean         
movements have in past times entirely   
compensated for the  waste produced by  
the denuding forces ever at work upon   
our globe4 ,but  this is not all4 ,the  
subterranean forces not only produce    
upheaval2  in a great many cases the    
evidences of subsidence are as clear and
  conclusive as are those of upheaval in
 others4 ,hence we are driven to        
conclude that the forces producing      
upheaval of portions of the earth's     
crust are sufficient1 not only to       
balance those producing subsidence1  but
 also to compensate for the destructive 
action of denuding agents  upon the     
land-masses of the globe4    ,it is only
 by a careful and attentive study and   
calculation of the  effects produced by 
the denuding agents at work all around  

us1 aided  by an examination of the     
enormous thicknesses of strata formed by
 the  action of such causes during past 
geological times1 that we are able  to  
form any idea of the reality and        
vastness of the agents of change  which 
are ever operating to modify the earth's
 external features4 ,when  we have      
clearly realised the grand effects      
produced on the surface  of the globe by
 these external forces1 through the     
action of its  investing atmosphere and 
circulating waters1 then1 and only then1
  shall we be in a position to estimate 
the far greater effects resulting  from 
the internal forces1 of which the most  
striking1 but not the most  important1  
results are seen in the production of   
volcanic eruptions and                  
earthquake-shocks4    ,another series of
 facts which serve to convince the      
geologist of the  reality and potency of
 the forces ever at work within the     
earth's  crust1 and the way in which    
these have operated during past         

geological  periods1 is found in the    
disturbed condition of many of the      
stratified  rock-masses of which it is  
composed4 ,such stratified rock-masses1 
it is  clear1 must have been originally 
deposited in a position of approximate  
horizontality2 but they are now often   
found in inclined and even  vertical    
positions2 they are seen to be bent1    
crumpled1 puckered1 and  folded in the  
most remarkable manner1 and have not    
unfrequently been  broken across by     
dislocations--'faults'--which have      
sometimes displaced  masses1 originally 
in contact1 to the extent of thousands  
of feet4  ,the slate-rocks of the globe1
 moreover1 bear witness to the fact that
  strata have been subjected to the     
action of lateral compression of        
enormous violence and vast duration2    
while in the metamorphic rocks  we see  
the effects of still more extreme       
mechanical strains1 which  have been in 
part transformed into chemical action4  
,no one who has  not studied the        

crushed1 crumpled1 fractured1 and       
altered condition  of many of the       
sedimentary rocks of the globe1 can form
 the faintest  idea of the enormous     
effects of the internal forces which    
have been in  operation within the      
earth's crust during earlier geological 
periods4  ,and it is only by such       
studies as these that we at last learn  
to regard  the earthquake and volcanic  
phenomena of our globe1 not as the      
grandest  and most important effects of 
these forces1 but as their secondary    
and accidental accompaniments4          
',volcanoes1' it has been said1 'are    
the safety-valves of the globe2' and    
when we come to realise the real  extent
 and nature of the internal forces      
ceaselessly working in the  earth's     
crust we shall scarcely be disposed to  
regard the simile as an  overstrained   
one4    ,sidenote3 ,,relation ,,to      
,,continental ,,movements4    ,the first
 geologist who attempted to show the    
exact relations existing  between those 

subterranean forces which cause the     
movements of  continental masses of     
land1 and those more startling displays 
of energy  which are witnessed in       
volcanic outbursts1 was the late ,mr4   
,poulett  ,scrope4 ,at a somewhat later 
date ,mr4 ,darwin1 in his remarkable    
paper  ',on the ,connexion of certain   
,volcanic ,phenomena in ,south ,america1
 and  on the ,formation of              
,mountain-chains and ,volcanoes as the  
effect of  ,continental ,elevations1'   
threw much new and important light upon 
the  question4    ,while1 on the one    
hand1 we are led by recent geological   
investigations  to reject the notions   
which were formerly accepted1 by which  
mountain-ranges were supposed to be     
suddenly and violently upheaved by      
volcanic forces1 we are1 on the other   
hand1 driven to conclude that  without  
the action of these subterranean forces1
 the irregularities  which are exhibited
 on the earth's surface could not have  
had any  existence4    ,it is true that 

the actual forms of the mountain-ranges 
are due  directly to the action of      
denuding forces1 which have sculptured  
out from the rude rocky masses all the  
varied outlines of peaks and  crags1 of 
ravines and valleys4 ,but it is none the
 less true that  the determining causes 
which have directed and controlled all  
this  earth-sculpture1 are found in the 
relative positions of hard and soft     
masses of rock2 but these rock-masses   
have acquired their hardness and        
consistency1 and have assumed their     
present positions1 in obedience  to the 
action of subterranean forces4 ,hence we
 see that though the  formation of      
mountain-ranges is proximately due to   
the denuding  forces1 which have        
sculptured the earth's surface1 the     
primary cause  for the existence of such
 mountain-chains must be sought for in  
the  fact that subterranean forces have 
been at work1 folding1 crumpling1  and  
hardening the soft sediments1 and       
placing them in such positions  that1 by

 the action of denudation1 the more     
indurated portions are left  standing as
 mountain-masses above the general      
surface4    ,the old notion that        
mountain-chains are due to a vertical   
upthrust  from below1 finds but little  
support when we come to study with due  
care the positions of the rock-masses   
composing the earth's crust4 ,on  the   
contrary1 we find that mountain-ranges  
are usually carved out of  the crushed  
and crumpled edges of strata which have 
along certain lines  been influenced by 
great mechanical strains1 and subjected 
to more or  less induration and chemical
 alteration4 ,when we compare these     
folded  and contorted portions of the   
strata with those parts of the same beds
  which are not so affected1 we find the
 effects produced in the former  are not
 such as would result from an upthrust  
from below1 but from  movements by which
 a tangential strain would be brought   
about4 ,if we  imagine certain lines of 
weakness to exist in the solid crust of 

the  earth1 then any movements in the   
portions of the crust between these     
lines of weakness would cause crushing  
and crumpling of the strata  along the  
latter4    ,sidenote3 ,,formation ,,of  
,,mountain-,,chains4    ,recent         
investigations of ,dana and other       
authors have thrown much new  light upon
 the question of the mode of formation  
of mountain-chains1  and the relation   
between the movements by which they are 
produced and  the sudden and violent    
manifestations of force witnessed in    
volcanic  outbursts4 ,we cannot1        
perhaps1 better illustrate this subject 
than by  giving a sketch of the series  
of operations to which the great ,alpine
  chains owe their origin4    ,there are
 good grounds for believing that the    
great mountain-axis of  ,southern       
,europe1 with its continuation in ,asia1
 had no existence  during the earlier   
geological periods4 ,indeed1 it has been
 proved that  all the higher among the  
existing mountain-chains of the globe   

have  been almost entirely formed in    
,tertiary times4 ,the reason of this    
remarkable fact is not far to seek4 ,so 
rapid is the work of denudation  in the 
higher regions of the atmosphere1 that  
the elevated crags and  pinnacles are   
being broken up by the action of        
moisture and frost at  an exceedingly   
rapid rate4 ,this fact is attested by   
the existence  of those enormous masses 
of angular rock-fragments which are     
found  lodged on every vantage-ground   
among the mountain-summits1 as well as  
by the continually descending materials 
which are borne by glaciers  and        
mountain-torrents to the valleys below4 
,where such a rate of  disintegration as
 this is maintained1 no elevated        
mountain-crests  could exist through    
long geological periods4 ,it is true we 
find in all  parts of the globe relics  
of many mountain-chains which were      
formed  before the ,tertiary period2 but
 these have by long-continued denudation
  been worn down to 'mere stumps4' ,of  

such worn-down and degraded             
mountain-ranges we have examples in the 
,scandinavian chains1 and some  of the  
low mountain-regions of ,central ,europe
 and ,north ,america4    ,let us now    
proceed to illustrate this subject by   
briefly sketching the  history of that  
series of operations by which the great 
mountain-chains  of the ,alpine system  
have been formed4    ,the first stage of
 that grand series of operations appears
 from recent  geological researches to  
have consisted in the opening of a      
number  of fissures running along a line
 near to that at which1 in a long       
subsequent period1 the elevation of the 
mountain-masses took place4  ,this      
betrayal of the existence of a line of  
weakness in this part of  the earth's   
crust occurred in the ,permian period1  
and from that time  onward a series of  
wonderful movements and changes have    
been going  forward1 which have resulted
 in the production of the ,alpine chains
 as  we now see them4    ,sidenote3     

,,volcanic ,,fissures ,,of ,,permian    
,,period4    ,from the great fissures   
opened in ,permian times along this line
 of  weakness1 great quantities of lava1
 scori1 and tuff were poured out1  and  
these accumulated to form great volcanic
 mountains1 which we can  now only study
 at a few isolated spots1 as in the     
,tyrol1 ,carinthia1  and about ,lake    
,lugano4 ,everywhere else1 these        
,permian volcanic rocks  appear to be   
deeply buried under the later-formed    
sediments1 from which  the ,alpine      
chains have been carved4 ,few and       
imperfect1 however1 as are  the         
exposures of these ancient rhyolite and 
quartz-andesite lavas and  agglomerates 
formed at the close of the ,palozoic    
epoch1 their greatly  denuded relics    
form masses which are in places more    
than #i1jjj feet in  thickness4 ,from   
this fact we are able to form some      
slight idea of the  scale upon which the
 volcanic outbursts in question must    
have taken  place during ,permian times4

    ,the second stage in the series of  
operations by which the ,alpine chains  
have been formed1 consisted in a general
 sinking of the surface along  that line
 of weakness in the earth's crust1 the  
existence of which had  been betrayed by
 the formation of fissures and the      
eruption of volcanic  rocks4 ,we have   
already had occasion to remark how      
frequently such  subsidences follow upon
 the extrusion of volcanic masses at any
 part  of the earth's surface2 and we   
have referred these downward movements  
in part to the removal of support from  
below the portion of the crust          
affected1 and in part to the weight of  
the materials piled upon its  surface by
 the volcanic forces4    ,the volcanic  
energy which had been manifested with   
such violence  during the ,permian      
period1 does not appear to have died out
 altogether  during the succeeding      
,triassic period4 ,a number of smaller  
volcanic  vents were opened from time to
 time1 and from these1 lavas1 tuffs1 and

  agglomerates1 chiefly of basic        
composition1 were poured out4 ,the      
relics  of these old ,triassic volcanoes
 are found at many points along the     
,alpine chain1 but it is evident that   
the igneous forces were gradually       
becoming exhausted during this period1  
and before the close of it they  had    
fallen into a state of complete         
extinction4    ,but the great subsidence
 which had commenced in the ,triassic   
period1  along what was to become the   
future line of the ,alpine chain1 was   
continued almost without interruption   
during the ,rhtic1 the ,jurassic1  the  
,tithonian1 the ,neocomian1 the         
,cretaceous and the ,nummulitic         
periods4 ,with respect to the strata    
formed during all these periods1  it is 
found that their thiknesses1 which away 
from the ,alpine axis  may be measured  
by hundreds of feet1 is along that axis 
increased  to thousands of feet4 ,the   
united thickness of sediments           
accumulated  along this great line of   

subsidence between the ,permian and     
,nummulitic  periods probably exceeds   
#fj1jjj feet1 or ten miles4 ,the        
subsidence  appears to have been very   
slow and gradual1 but almost            
uninterrupted1  and the deposition of   
sediments seems to have kept pace with  
the  sinking of the sea-bottom1 a fact  
which is proved by the circumstance     
that nearly the whole of these sediments
 were such as must have been            
accumulated in comparatively shallow    
water4    ,sidenote3 ,,formation ,,of   
,,alpine ,,geosynclinal4    ,by the     
means we have described there was thus  
formed a 'geosynclinal1'  as geologists 
have called it1 that is1 a trough-like  
hollow filled  with masses of abnormally
 thickened sediments1 which had been    
piled  one upon another during the long 
periods of time in which almost         
uninterrupted subsidence was going on   
along the ,alpine line of  weakness in  
the earth's crust4 ,in this way was     
brought together that  enormous         

accumulation of materials from which the
 hard masses of the  ,alpine chains were
 subsequently elaborated1 and out of    
which the  mountain-peaks were          
eventually carved by denudation4    ,the
 third stage in this grand work of      
mountain-making commenced in the        
,oligocene period4 ,it consisted of a   
series of movements affecting the  parts
 of the earth's crust on either side of 
the line of weakness  which had first   
exhibited itself in ,permian times4 ,by 
these movements  a series of tangential 
strains were produced1 which resulted in
 the  violent crushing1 folding1 and    
crumpling of the sedimentary materials  
composing the geosynclinal4    ,one     
effect of this action was the violent   
flexure and frequent fracture  of these 
stratified masses1 which are now found  
in the ,alpine regions  assuming the    
most abnormal and unexpected positions  
and relations to  one another4          
,sometimes the strata are found tortured
 and twisted into  the most complicated 

folds and puckerings2 at others they are
 seen to  be completely inverted1 so    
that the older beds are found lying upon
 the  newer2 and in others1 again1 great
 masses of strata have been traversed   
by numerous fractures or faults1 the    
rocks on either side of which are       
displaced to the extent of thousands of 
feet4    ,another effect of the great   
lateral thrusts by which the thick      
sedimentary masses of the geosynclinal  
were being so violently  disturbed1 was 
the production of a great amount of     
induration and  chemical change in these
 rocks4 ,masses of soft clay1 of the age
 of  that upon which ,london is built1  
were by violent pressure reduced to  the
 condition of roofing-slate1 similar to 
that of ,north ,wales4 ,one  of the most
 important discoveries of modern times  
is that which has  resulted in the      
recognition of the fact of the mutual   
convertibility  of different kinds of   
energy4 ,we now know that mechanical    
force  may be transformed into          

heat-force or chemical force2 and of    
such  transformations we find abundant  
illustrations in the crushed and        
crumpled rock-masses of the ,alpine     
chains4    ,under the influence of these
 several kinds of force1 not only was   
extreme consolidation and induration    
produced among the rock-masses1  but    
chemical affinity and crystalline action
 had the fullest play  among the        
materials of which they were composed4  
,in many cases we find  the originally  
soft muds1 sands1 and shell-banks       
converted into the  most highly         
crystalline rocks1 which retain their   
primary chemical  composition1 but have 
entirely lost all their other original  
features4    ,sidenote3 ,,formation ,,of
 ,,alpine ,,geanticlinal4    ,to the    
mass of folded1 crumpled1 and altered   
strata1 formed from a  geosynclinal by  
lateral pressure1 geologists have given 
the name  of a 'geanticlinal4' ,the     
formation of the ,alpine geanticlinal   
was  due to movements which commenced in

 the ,oligocene period1 attained  their 
maximum in the ,miocene1 and appear to  
have declined and almost  altogether    
died out in the ,pliocene period4       
,the movements which resulted in the    
crushing and crumpling of the  thickened
 mass of sediments along the ,alpine    
line of weakness1 also  gave rise to the
 formation of a series of fissures from 
which volcanic  action took place4      
,these fissures were not1 however1      
formed along the  original line of      
weakness1 for this had been strengthened
 and repaired  by the deposition of     
ten-miles' thickness of sediments upon  
it1 but  along new fissures opened in   
directions parallel to the original     
lines  of weakness1 and in areas where a
 much less considerable amount of       
deposition had taken place since        
,permian times4    ,we have abundant    
evidence that1 just at the period when  
those great  movements were commencing  
which resulted in the formation of the  
great  ,alpine and ,himalayan           

geanticlinal1 earth-fissures were being 
opened  upon either side of the latter  
from which volcanic outbursts took      
place4 ,at the period when the most     
violent mountain-forming movements      
occurred1 these fissures were in their  
most active condition1 and at  this time
 two great volcanic belts stretched east
 and west1 on either  side of1 and      
parallel to1 the great ,alpine chain4   
,the ,northern volcanic  band was formed
 by the numerous vents1 now all extinct1
 in ,auvergne1  ,central ,germany1      
,bohemia1 and ,hungary1 and was probably
 continued in  the volcanoes of the     
,thian ,shan and ,mantchouria4 ,the     
,southern volcanic  band was formed by  
the numerous vents of the ,iberian and  
,italian  peninsulas1 and the islands of
 the ,mediterranean1 and were continued 
to the eastward by those of ,asia       
,minor1 ,arabia1 and the ,north ,indian 
,ocean4 ,as the earth-movements which   
produced the geanticlinal died  away1   
the volcanic energy along these parallel

 volcanic bands died  away at the same  
time4 ,in studying the geology of       
,central and ,southern  ,europe1 no fact
 comes out more strikingly than that of 
the synchronism  between the            
earth-movements by which the            
geanticlinal of the ,alps was  formed1  
and the volcanic manifestations which   
were exhibited along  lines of fissure  
parallel to that geanticlinal4 ,the     
earth-movements  and the volcanic       
outbursts both commenced in the         
,oligocene period1  gradually attained  
their maximum in the ,miocene1 and as   
slowly declined  in the ,pliocene4      
,sidenote3 ,,sculpturing ,,of ,,alps    
,,by ,,denudation4    ,the fourth stage 
in the great work of mountain-building  
in the case  of the ,alps consisted in  
the operation of the denuding forces1   
the  disintegrating action of rain and  
frost1 the transporting action  of      
rivers and glaciers1 by which the       
,alpine peaks were gradually  sculptured
 out of the indurated and altered masses

 constituting the  geanticlinal4 ,the   
action of this fourth stage went on to a
 great  extent side by side with that of
 the third stage4 ,so soon as the       
earth-movements had brought the         
submerged sedimentary masses of the     
geosynclinal under the action of the    
surface tides and currents of the       
ocean1 marine denudation would commence2
 and1 as the work of elevation  went on1
 the rock-masses would gradually be     
brought within the reach  of those more 
silently-working but far more effective 
agents which  are ever operating in the 
higher regions of the atmosphere4 ,it is
  impossible to say what would have been
 the height of the ,alpine chain  if the
 work of denudation had not to a great  
extent kept pace with  that of          
elevation4 ,only the harder and more    
crystalline masses have  for the most   
part escaped destruction1 and stand up  
in high craggy  summits2 while flanking 
hills1 like the well-known ,rigi1 are   
,been to  be composed of conglomerates  

thousands of feet in thickness1 composed
  of their disintegrated materials4 ,it 
is a remarkable fact1 as showing  how   
enormous was the work of elevation      
daring the formation of the             
geanticlinal1 that some of the youngest 
and least consolidated rocks of  the    
,nummulitic period are still found at a 
height of #aa1jjj feet in the  ,alps1   
and of #af1jjj feet in the ,himalaya4   
,from what has been said1 it will be    
seen that mountain-chains may be        
regarded as cicatrised wounds in the    
earth's solid crust4 ,a line of         
weakness first betrays itself at a      
certain part of the earth's surface  by 
fissures1 from which volcanic outbursts 
take place2 and thus the  position of   
the future mountain-chain is determined4
 ,next1 subsidence  during many millions
 of years permits of the accumulation of
 the raw  materials out of which the    
mountain-range is to be formed2         
subsequent  earth-movements cause these 
raw materials to be elaborated into the 

hardest and most crystalline            
rock-masses1 and place them in elevated 
and favourable positions2 and lastly1   
denudation sculptures from these        
hardened rock-masses all the varied     
mountain forms4 ,thus the work of       
mountain-making is not1 as was formerly 
supposed by geologists1 the  result of a
 simple upheaving force1 but is the     
outcome of a long and  complicated      
series of operations4    ,sidenote3     
,,origin ,,of ,,other                   
,,mountain-,,chains4    ,the careful    
study of other mountain-chains1         
especially those of the  ,american      
continent1 has shown that the series of 
actions which we  have described as     
occurring in the ,alps1 took place in   
the same order  in the formation of all 
mountain-masses4 ,it is doubtful whether
 the  line of weakness is always        
betrayed in the first instance by the   
formation along its course of volcanic  
fissures4 ,but in all cases we  have    
evidence of the production of a         

geosynclinal1 which is afterwards1  by  
lateral pressure1 converted into a      
geanticlinal1 and from this the         
mountain-chains have been carved by     
denudation4 ,professor ,dana has  shown 
that the geosynclinal of the            
,appalachian chain was made up of       
sediments attaining a thickness of      
#dj1jjj feet1 or eight miles2 while     
,mr4 ,clarence ,king has shown that a   
part of the geosynclinal of the  ,rocky 
,mountains was built up of no less than 
#fj1jjj feet1 or twelve  miles of       
strata4    ,it has thus been established
 that a very remarkable relation exists 
between the forces by which continental 
masses of land are raised  and          
depressed1 and mountain-ranges have been
 developed along lines  of weakness     
separating such moving continental      
masses1 and those  more sudden and      
striking manifestations of energy which 
give rise to  volcanic phenomena4 ,it is
 in this relation between the widespread
  subterranean energies and the local   

development of the same forces  at      
volcanic vents1 that we must in all     
probability seek for the  explanation of
 those interesting peculiarities of the 
distribution  of volcanoes upon the face
 of the globe which we have described   
in a former chapter4 ,the parallelism of
 volcanic bands to great                
mountain-chains is thus easily accounted
 for2 and in the same way  we may       
probably explain the position of most   
volcanoes with regard  to coast-lines4  
,we have already pointed out the        
objections to the  commonly-received    
view that volcanoes depend for their    
supplies of  water on the proximity of  
the ocean4 ,this proximity of the ocean 
to  volcanic vents we are thus inclined 
to regard1 not as the cause1 but as  the
 effect of the subterranean action4 ,the
 positions of both volcanoes  and       
coast-lines are determined by the limits
 of those great areas of  the earth's   
crust which are subjected to slow       
vertical movements1 often  in opposite  

directions4    ,terrible and striking1  
then1 as are the phenomena connected    
with  volcanic action1 such sudden and  
violent manifestations of the           
subterranean energy must not be regarded
 as the only1 or indeed the  chief1     
effects which they produce4 ,the        
internal forces continually  at work    
within the earth's crust perform a      
series of most important  functions in  
connection with the economy of the      
globe1 and were the  action of these    
forces to die out1 our planet would soon
 cease to be  fit for the habitation of 
living beings4    ,there is no fact     
which the geological student is more    
constantly  called upon to bear in mind 
than that of the potency of seemingly   
insignificant causes which continue in  
constant operation through long  periods
 of time4 ,indeed these small and almost
 unnoticed agencies at  work upon the   
earth's crust are often found1 in the   
long ran1 to  produce far grander       
effects than those of which the action  

is much  more striking and obvious4 ,it 
is to the silent and imperceptible      
action of atmospheric moisture and frost
 that the disintegration of  the solid  
rock-masses must be mainly ascribed2 and
 the noisy cataract  and ocean-billow   
produce effects which are quite         
insignificant  compared with those which
 must be ascribed to the slight and     
almost  unnoticed forces4 ,great masses 
of limestone are built up of the remains
  of microscopic organisms1 while the   
larger and higher life-forms  contribute
 but little to the great work of        
rock-building4    ,sidenote3 ,,effects  
,,of ,,slow ,,continental ,,movements4  
,in the same way it is to the almost    
unnoticed action of the  subterranean   
forces in raising some vast areas of the
 earth's crust1  in depressing others1  
and in bringing about the development of
  mountain-chains between them1 that we 
must ascribe a far more important  part 
in the economy of our globe than to the 
more conspicuous but less  constant     

action of volcanoes4    ,a few simple   
considerations will serve to convince   
us1 not only of the  beneficial effects 
of the action of the subterranean       
energies within  the earth's crust1 but 
of the absolute necessity of the        
continued  operation of those energies  
to the perpetuation of that set of      
conditions by which our planet is fitted
 to be the habitation of living  beings4
    ,we have already referred to the    
prodigious effects which are constantly 
being produced around us by the action  
of the external forces at work  upon the
 globe4 ,the source of these external   
forces is found in the  movements and   
changes which are ever going on within  
the aqueous and  atmospheric media in   
which the globe is enveloped4 ,the      
circulation of  the air1 influencing the
 circulation of the waters in the shape 
of  clouds1 rain1 snow1 rivers1         
glaciers1 and oceans1 causes the        
breaking  up of even the hardest        
rock-masses1 and the continual removal  

of their  disintegrated fragments from  
higher to lower levels4 ,this work goes 
on  with more or less regularity over   
every part of the land raised above  the
 level of the ocean1 but the rate of    
destruction in the higher  regions of   
the atmosphere is far more rapid than at
 lower levels4 ,hence  the circulating  
air and water of the globe are found to 
be continually  acting as levellers of  
the land-masses of the earth4    ,it is 
by no means a difficult task to         
calculate the approximate rate  at which
 the various continents and islands are 
being levelled down1  and such          
calculations prove that in a very few   
millions of years the  existing forces  
operating upon the earth's surface would
 reduce the  whole of the land-masses to
 the level of the ocean4    ,but a      
little consideration will convince us   
that the circulation of  the air and    
waters of the globe are themselves      
dependent upon the  existence of those  
irregularities of the land-surfaces     

which they are  constantly tending to   
destroy4 ,without elevated mountain     
ridges the  regular condensation of     
moisture1 and its collection and        
distribution  in streams and rivers over
 every part of the land surfaces1 could 
not take place4 ,under these            
circumstances the unchecked evaporation 
of the oceanic waters would probably go 
on1 till the proportion  of water-vapour
 increased to such an extent in the     
atmosphere as  effectually to destroy   
those nicely-balanced conditions upon   
which the  continued existence of both  
vegetable and animal life depend4       
,but the repeated upward and downward   
movements which have been shown  to be  
going on in the great land-masses of the
 globe1 giving rise  in turns to those  
lateral thrusts and tangential strains  
to which  mountain-chains owe their     
formation1 afford a perfect compensation
  to the action of the external forces  
ever operating upon the earth's         
surface4    ,if1 however1 the           

uncompensated effect of the external    
forces acting on  the earth's crust is  
calculated to bring about the           
destruction of those  conditions upon   
which the existence of life depends1 the
 uncompensated  effect of the internal  
forces acting on the earth's crust are  
fraught  with at least equal dangers to 
those necessary conditions4             
,sidenote3 ,,contrast ,,between ,,the   
,,earth ,,and ,,moon4    ,in our nearest
 neighbour among the planets--the       
moon--the telescope has  revealed to us 
the existence of a globe1 in which the  
internal forces  have not been checked  
and controlled by the operation of any  
external  agencies--for the moon appears
 to be destitute of both atmosphere and 
water4    ,under these circumstances we 
find its surface1 as we might expect1 to
  be composed of rocks which appear to  
be entirely of igneous origin2  the     
mountain-masses1 unworn by rain or      
frost1 river or glacier1 being  of most 
prodigious dimensions as compared with  

those of our own globe1  while no       
features at all resembling valleys1 or  
plains1 or alluvial  flats are anywhere 
to be discerned upon the lunar surface4 
,but by the admirable balancing of the  
external and internal forces  on our own
 globe1 the conditions necessary to     
animal and vegetable  existence are     
almost constantly maintained1 and those 
interruptions  of such conditions1      
produced by hurricanes and floods1 by   
volcanic  outbursts and earthquakes1 may
 safely be regarded as the insignificant
  accidents of what is1 on the whole1 a 
very perfectly working piece of         
machinery4    ,the ancients loved to    
liken the earth to a living being--the  
macrocosm  of which man was the puny    
representative or microcosm2 and when we
  study the well-adapted interplay of   
the forces at work upon the  earth's    
crust1 both from within and without1 the
 analogy seems a  scarcely strained one4
 ,in the macrocosm and the microcosm    
alike1 slight  interferences with the   

regular functions occasionally take     
place1 and  both of them exhibit the    
traces of a past evolution and the germs
 of an  eventual decay4                 
,,chapter ,,xi4    ,,what ,,volcanoes   
,,teach ,,us ,,concerning ,,the ,,nature
 ,,of ,,the ,,earth',s ,,interior4      
,in entering upon any speculations or   
enquiries concerning the nature of  the 
interior of our globe1 it is necessary  
before all things that we  should       
clearly realise in our minds how small  
and almost infinitesimal  is that part  
of the earth's mass which can be        
subjected to direct  examination4 ,the  
distance from the surface to the centre 
of our globe  is nearly #d1jjj miles1   
but the deepest mines do not penetrate  
to much  more than half a mile from the 
surface1 and the deepest borings fall   
far short of a mile in depth4           
,sometimes1 it is true1 the geologist   
finds means for drawing inferences as to
 the nature of the rocks at  depths of  
ten or fifteen miles below the surface2 

but the last-named  depth must be       
regarded as the utmost limit of that    
portion of our  globe which can be made 
the object of direct observation and    
study4  ,this thin exterior film of the 
earth's mass1 which the geologist is    
able to investigate1 we call the 'crust 
of the globe'2 but it must be           
remembered that in using this term1 it  
is not intended to imply that  the outer
 part of our globe differs in any       
essential respect from the  interior4   
,the term 'crust of the globe' is       
employed by geologists as  a convenient 
way of referring to that portion of the 
earth which is  accessible to their     
observation4    ,but if we are unable to
 make direct investigations concerning  
the  nature of the internal portions of 
the globe1 there are nevertheless a     
number of facts from which we may draw  
important inferences upon the  subject4 
,these facts and the inferences based   
upon them we shall now  proceed to      
consider4    ,first in importance among 

these we may mention the results which  
have  been obtained by weighing our     
globe4 ,various methods have been       
devised  for accomplishing this         
important object1 and the conclusions   
arrived  at by different methods agree  
so closely with one another1 that there 
is no room for doubt as to the          
substantial accuracy of those results4  
,it may be taken as proved beyond the   
possibility of controversy that  our    
globe is equal in weight to five and a  
half globes of the same size  composed  
of water1 or1 in other words1 that the  
average density of the  materials       
composing the globe is five and a half  
times as great as that  of water4       
,now the density of the materials which 
compose the crust of the globe  is very 
much less than this1 varying from about 
two-and-one-third to  three times that  
of water4 ,hence we are compelled to    
conclude that the  interior portions of 
the globe are of far greater density    
than the  exterior portions2 that1 as a 

matter of fact1 the mass of the globe is
  composed of materials having twice the
 density of the rocks exposed at  the   
surface4    ,sidenote3 ,,density ,,of   
,,earth',s ,,interior4    ,it has been  
sometimes argued that as all materials  
under intense  pressure appear to yield 
to an appreciable extent1 and to allow  
their  particles to be packed into a    
smaller compass1 we may find in this    
fact  an explanation of the great       
density of the internal parts of the    
globe4  ,it has in fact been suggested  
that under the enormous pressure which  
must be exerted by masses of rock       
several thousand feet in thickness1  the
 materials of which our earth is        
composed may be compelled to pack       
themselves into less than one-half the  
compass which they occupy at the        
surface4 ,but the ascription of such    
almost unlimited compressibility to     
solid substances can be supported       
neither by experiment nor analogy4      
,various considerations point to the    

probability that solid bodies yield  to 
pressure up to a certain limit and no   
farther1 and that when this  limit is   
reached an increase in pressure is no   
longer attended with a  reduction in    
bulk4    ,if then we are compelled to   
reject the idea of the unlimited        
compressibility of solid substances1 we 
must conclude that the interior         
portions of our globe are composed of   
materials of a different kind  from     
those which occur in its crust4 ,and    
this conclusion1 as we shall  presently 
see1 is borne out by a number of        
independent facts4    ,the study of the 
materials ejected from volcanic vents   
proves that even  at very moderate      
depths there exist substances differing 
greatly in  density1 as well as in      
chemical composition4 ,the lightest     
lavas have a  specific gravity of #bc1  
the heaviest of over #c4 ,and that      
materials of  even greater density are  
sometimes brought by volcanic action    
from the  earth's interior1 we have now 

the clearest proofs4    ,sidenote3      
,,relation ,,between ,,earth ,,and      
,,other ,,planets4    ,but in           
considering a question of this kind1 it 
will be well to remember  that analogy  
may furnish us with hints upon the      
subject which may prove  to be by no    
means unimportant4 ,there is no question
 upon which modern  science has wrought 
out a more complete revolution in our   
ideas1 than  that of the relation of our
 earth to the other bodies of the       
universe4  ,we know1 as the result of   
recent research1 that our globe is one  
of  a great family of bodies1 moving    
through space in similar paths and  in  
obedience to the same laws4 ,a hundred  
years ago the primary and  secondary    
planets of the solar system could be    
almost numbered upon  the fingers2 now  
we recognise the fact that they exist in
 countless  millions1 presenting every  
variety of bulk from masses #a1djj times
  as large as our earth down to the     
merest planetary dust4 ,between the     

orbits of ,mars and ,jupiter1 more than 
#bjj small planets have been  recognised
 as occurring1 and every year additions 
are made to the  number of these        
asteroids4 ,comets have now been        
identified with streams  of such        
planetary bodies1 of minute size1 moving
 in regular orbits  through our system4 
,the magnificent showers of             
'shooting-stars' have  been proved to be
 caused by the passage of the earth     
through such  bands of travelling       
bodies1 and 'the zodiacal light' finds  
its most  probable explanation in the   
supposition that the sun is surrounded  
by  a great mass of such minute planets4
 ,every increase in the power of  the   
telescope reveals to us the existence of
 new secondary planets  or moons1       
revolving about the primaries2 and the  
wonderful system  of the ,saturnian     
rings is now explained by the proved    
existence of  great streams of such     
secondary planets circling around it4   
,the solar  system was formerly         

conceived of as a vast solitude through 
which a  few gigantic bodies moved at   
awful distances from one another4 ,now  
we  know that the supposed empty void is
 traversed by countless myriads of      
bodies of the most varied dimensions1   
all moving in certain definite  paths1  
in obedience to the same laws1 ever     
acting and reacting upon  each other1   
and occasionally coming into collision4 
,there are not wanting further facts to 
prove that the other planets are  like  
our own in many of their phenomena and  
surroundings4 ,in some of  them         
atmospheric phenomena have been         
detected1 such as the formation of      
clouds and the deposition of snow1 so   
that the external forces at work  on our
 globe act upon them also4 ,and that    
internal forces1 like those  we have    
been considering in the case of our     
earth1 are at work in our  neighbours1  
is proved by the great solar storms and 
the condition of  the moon's surface4   
,but the results of spectrum-analysis in

 recent years have furnished new  facts 
in proof of the close relationship of   
our earth to the numerous  similar      
bodies by which it is surrounded4 ,so   
far as observation has yet  gone we have
 reason for believing that not only the 
members of the  solar system1 but the   
more distant bodies of the universe1 are
 all  composed of the same elementary   
substances as those which enter into    
the composition of our globe4    ,the   
most satisfactory information concerning
 the composition and nature  of other   
planetary bodies is derived from the    
study of those small  planets which     
occasionally come into collision with   
our globe1 and  which have their own    
proper motion in space thereby arrested4
 ,these  meteorites1 as such falling    
planetary bodies are called1 have justly
  attracted great attention1 and their  
fragments are treasured as the  most    
valuable objects in our museums4        
,sidenote3 ,,composition ,,of           
,,meteorites4    ,the first fact        

concerning these meteorites1 which it is
 necessary  to notice1 is that they are 
composed of the same chemical elements  
as occur in the earth's crust4 ,no      
element has yet been found in any       
meteorite which was not previously known
 as existing in the earth1 and  of the  
sixty-five or seventy known terrestrial 
elements no less than  twenty-two have  
already been detected in meteorites4    
,there are1 however1 a dozen elements   
which occur in overwhelming  proportions
 in the earth's crust4 ,we shall        
probably not be going too  far in saying
 that these twelve elements--namely1    
oxygen1 silicon1  aluminium1 calcium1   
magnesium1 sodium1 potassium1 iron1     
carbon1  hydrogen1 sulphur1 and         
chlorine--make up amongst them not less 
than #iii  out of #a1jjj parts of the   
earth's crust1 and that all the other   
fifty  or sixty elements are #hj        
comparatively rare that they do not     
constitute  when taken altogether more  
than one part in #a1jjj of the rocks of 

the  globe4 ,now all of these twelve    
common terrestrial elements occur in    
meteorites1 and the fact that the rarer 
terrestrial elements have not  as yet   
been found in them will not surprise    
anyone1 who remembers how  small is the 
bulk of all the specimens of these      
meteorites existing in  our museums4    
,we have hitherto insisted on the points
 of resemblance in the chemical         
composition of meteorites and that of   
the rocks of the globe1 but we  shall   
now have to indicate some very important
 points in which they  differ4    ,while
 in the rocks composing the earth's     
crust oxygen forms one-half of  their   
mass1 and silicon another quarter1 we   
find that in the meteorites  these      
elements1 though present1 play a much   
less important part4 ,the  most abundant
 element in the meteorites is iron2 and 
nickel1 chromium1  cobalt1 manganese1   
sulphur1 and phosphorus1 are much more  
abundant in  these extra-terrestrial    
bodies than they are in the earth's     

crust4    ,we have already referred to  
the remarkable fact that in our earth's 
crust nearly all the other elementary   
substances are found combined  in the   
first instance with oxygen1 and that    
most rocks consist of the  oxide of     
silicon combined with the oxides of     
various metals4 ,but this  is by no     
means the case with the meteorites4 ,in 
them we find metals  like iron1 nickel1 
cobalt1 c41 in their uncombined         
condition1 and  forming alloys with one 
another4 ,the same and other metals also
 occur  in combination with carbon1     
phosphorus1 chlorine1 and sulphur1 and  
some of the substances thus formed are  
quite unknown among terrestrial  rocks4 
,compounds of the oxide of silicon with 
the oxides of the metals  such as form  
the mass of the crust of the globe do   
occur in meteorites1  but they play a   
much less important part than in the    
case of the  terrestrial rocks4         
,among the substances found in          
meteorites are several which do not     

exist  among the terrestrial            
rocks--some1 indeed1 which it seems     
impossible  to conceive of as being     
formed and preserved under terrestrial  
conditions4 ,among these we may mention 
the phosphide of iron and nickel        
7,schreibersite71 the sulphide of       
chromium and iron 7,daubrelite71 the    
protosulphide of iron 7,troilite71 the  
sulphide of calcium 7,oldhamite71  the  
protochloride of iron 7,lawrencite71 and
 a peculiar form of  crystallised       
silica1 called by ,professor ,maskelyne 
',asmanite4'    ,sidenote3 ,,different  
,,kinds ,,of ,,meteorites4    ,there are
 other phenomena exhibited by meteorites
 which indicate that  they must have    
been formed under conditions very       
different to those  which prevail upon  
the earth's surface4 ,thus we find that 
fused iron  and molten slag-like        
materials have remained entangled with  
each other1  and have not separated as  
they would do if a great body like the  
earth  were near to exercise the varying

 force of gravity upon the two  classes 
of substances4 ,again1 meteorites are   
found to have absorbed  many times their
 bulk of hydrogen gas1 and to exhibit   
peculiarities in  their microscopic     
structure which can probably be only    
accounted for  when we remember that    
they were formed in the interplanetary  
spaces1  far away from any great        
attracting body4    ,but in recent years
 a number of very important facts have  
been  discovered which may well lead us 
to devote a closer attention to the     
composition and structure of meteorites4
 ,it has been shown1 on the  one hand1  
that some meteorites contain substances 
precisely similar  to those which are   
sometimes brought from the earth's      
interior during  volcanic outbursts2    
and1 on the other hand1 there have been 
detected1  among some of the ejections  
of volcanoes1 bodies which so closely   
resemble meteorites that they were long 
mistaken for them4 ,both kinds  of      
observation seem to point to the        

conclusion that the earth's  interior is
 composed of similar materials to those 
which we find in the  small planets     
called meteorites4    ,m4 ,daubre has   
proposed a very convenient              
classification for  meteorites1 dividing
 them into the following four groups3-- 
,i4 ,holosiderites2 consisting almost   
entirely of metallic iron1 or of  iron  
alloyed with nickel1 stony matter being 
absent2 but sulphides1  phosphides1 and 
carbides of several metals are often    
diffused through  the mass4 ,the        
polished surfaces of these meteoric     
irons1 when etched  with acid1 often    
exhibit a remarkable crystalline        
structure4    ,,ii4 ,syssiderites2 in   
which a network of metallic iron        
encloses a  number of granular masses of
 stony materials4    ,,iii4             
,sporadosiderites2 which consist of a   
mass of stony materials1  through which 
particles of metallic iron are          
disseminated4    ,,iv4 ,asiderites2     
containing no metallic iron1 but        

consisting entirely  of stony materials4
    ,there are1 besides the meteorites  
belonging to these principal groups1  a 
few of peculiar and exceptional         
composition1 which we need not notice   
further for our present purpose4        
,from the above classification it will  
be seen that most meteorites  consist of
 a mixture in varying proportions of    
metallic and stony  materials4          
,sometimes the metallic constituents are
 present in greater  proportions than   
the stony1 at other times the stony     
materials  predominate1 while           
occasionally one or other of these      
elements may be  wholly wanting4    ,the
 stony portions of meteorites1 upon     
careful examination1 prove to be  built 
up of certain minerals1 agreeing in     
their chemical composition  and their   
crystalline forms with those which occur
 in the rocks of the  earth's crust4    
,among the ordinary terrestrial minerals
 occurring in  the stony portions of    
meteorites1 we may especially mention   

olivine1  enstatite1 augite1 anorthite1 
chromite1 magnetite1 and pyrrhotite4    
,sidenote3 ,,meteorites ,,and           
,,ultra-,,basic ,,rocks4    ,the        
minerals which occur in meteorites are  
in every case such as are  found in the 
more basic volcanic rocks--quartz1 and  
the acid felspars1  with the other      
minerals which occur in acid rocks1     
being entirely  absent in the           
'extra-terrestrial' rocks4    ,now1     
besides the three great classes of lavas
 which we have described  as being      
ejected from volcanic vents1 there are  
some rarer materials  occasionally      
brought from the earth's interior by the
 same agency1  that present a most      
wonderful resemblance to the stony      
portions of  meteorites4 ,these         
materials we may call 'ultra-basic      
rocks4' ,their  specific gravity is very
 high1 usually exceeding #c1 and they   
contain  a very low percentage of       
silica2 on the other hand1 the          
proportion of  iron and magnesia is     

often much greater than in ordinary     
terrestrial  rocks4 ,but the most       
remarkable fact about these ultra-basic 
rocks is1  that they are almost entirely
 composed of the minerals which occur in
  meteorites2 namely1 olivine1          
enstatite1 augite1 anorthite1 magnetite1
  and chromite4    ,the ultra-basic     
rocks often occur under very peculiar   
conditions4  ,sometimes they are found  
forming ordinary volcanic protrusions   
through the sedimentary rocks4 ,the     
rocks named pikrites1 lherzolites1      
dunites1 c41 are examples of such       
igneous protrusions composed of  these  
ultra-basic materials1 and probably all 
the true serpentines are  rocks of the  
same class which have absorbed water and
 undergone great  alteration4 ,the      
ultra-basic rocks sometimes contain     
platinum and other  metals in the free  
or uncombined state4 ,but not           
unfrequently we find  among the ordinary
 ejections of volcanoes1 nodules and    
fragments of  such ultra-basic          

materials1 which have clearly been      
carried up with the  other lavas from   
great depths in the earth's crust4 ,thus
 in ,auvergne1  the ,eifel1 ,bohemia1   
,styria1 and many other volcanic        
districts1 the  basaltic lavas and tuffs
 are found to contain nodules composed  
of  the minerals which are so highly    
characteristic of meteorites4 ,such     
nodules1 too1 often form the centres of 
the volcanic bombs which are  thrown out
 of craters during eruptions4    ,we    
thus see that materials identical in    
composition and character with  the     
stony portions of meteorites1 exist     
within the earth's interior1  and are   
thrown out on its surface by volcanic   
action4 ,a still more  interesting      
discovery has been made in recent years2
 namely1 that  materials similar to the 
metallic portion of meteorites1 and     
consisting  of nickeliferous iron1 also 
occur in deep-seated portions of the    
earth's crust1 and are brought to the   
surface during periods of igneous       

activity4    ,in the year #ahgj1        
,professor ,nordenskild made a most     
important  discovery at ,ovifak1 on the 
south side of the ,island of ,disko1 off
  the ,greenland coast4 ,on the shore of
 the island a number of blocks of  iron 
were seen1 and the chemical examination 
of these proved that1  like ordinary    
metallic meteorites1 they consisted of  
iron alloyed with  nickel and cobalt4   
,sidenote3 ,,iron-,,masses ,,of         
,,ovifak4    ,now1 when the facts       
concerning the masses of native iron of 
,ovifak were  made known1 the first and 
most natural explanation which presented
  itself to every mind was1 that these  
were a number of meteorites which  at   
some past period had fallen upon the    
earth's surface4      ,metallic iron4   
,opaque crystals of magnetite 7black    
oxide of iron74      ,transparent       
crystals of felspar1 augite1 and        
olivine4    ,illustration3 ,fig4        
#hg4--,section of basalt from ,ovifak1  
,greenland1 with  particles of metallic 

iron diffused through its mass4    ,but 
a further examination of the locality   
revealed a number of facts  which1 as   
,professor ,steenstrup pointed out1 it  
is very difficult  to reconcile with the
 theory that the ,ovifak masses of iron 
are of  meteoric origin4 ,the district  
of ,western ,greenland1 where these     
masses  were discovered1 has been the   
scene of volcanic outbursts on the      
grandest scale during the ,miocene      
period4 ,in close proximity to the      
great iron masses1 there are seen a     
number of basaltic dykes2 and1 when     
these dykes are carefully examined1 the 
basaltic rock of which they are         
composed is seen to be full of particles
 of metallic iron4 ,in fig4 #hg1  we    
have a drawing made from a section of   
the ,ovifak basalts magnified  four or  
five diameters4 ,the rock-mass is seen  
to be composed of black1  opaque        
magnetite1 and transparent crystals of  
augite1 labradorite1  olivine1 c42      
while1 through the whole1 particles of  

metallic iron are  found entangled among
 the different crystals in the most     
remarkable  manner4    ,it has been     
suggested that this singular rock might 
have been formed by  a meteorite        
falling1 in ,miocene times1 into a      
lava-stream in a state  of              
incandescence4 ,but the relation of the 
metallic particles to the  stony        
materials is such as to lend no support 
whatever to this rather  strained       
hypothesis4    ,a careful study of all  
the facts of the case by ,lawrence      
,smith1  ,daubre1 and others well       
acquainted with the phenomena exhibited 
by  meteorites1 has led to the          
conclusion that the large iron-masses of
  ,ovifak1 as well as the particles of  
metallic iron diffused through  the     
surrounding basalts1 are all of         
terrestrial origin1 and have been       
brought by volcanic action from the     
earth's interior4 ,it is probable  that1
 just as we find in many basaltic lavas 
nodules of ultra-basic  materials       

similar to the stony parts of           
meteorites1 so in these basalts  of     
,ovifak we have masses of iron alloyed  
with nickel1 similar to the  metallic   
portions of meteorites4 ,both the stony 
and metallic enclosures  in the basalt  
are in all probability derived from     
deeper portions of  the earth's crust4  
,by the weathering away of the basalt of
 ,ovifak1 the  larger masses of metallic
 iron have been left exposed upon the   
shore  where they were found4    ,there 
are a number of other facts which seem  
to support this startling  conclusion4  
,thus it has been shown by ,professor   
,andrews that certain  basalts in our   
own islands contain particles of        
metallic iron of  microscopic           
dimensions1 and it is not improbable    
that some of the  masses of             
nickeliferous iron found in various     
parts of the earth's  surface1 which    
have hitherto been regarded as          
meteorites1 are1 like  those of ,ovifak1
 of terrestrial origin4    ,sidenote3   

,,materials ,,filling                   
,,metallic-,,veins4    ,another piece of
 evidence pointing in the same          
direction1 is derived  from those great 
fissures communicating with the interior
 of our globe  which become filled with 
metallic minerals1 and are known to us  
as  mineral-veins4 ,in these            
mineral-veins the native metals1 their  
alloys1  and combinations of these with 
sulphur1 chlorine1 phosphorus1 c41 are  
frequently present4 ,but oxides of the  
metals1 except as products of           
subsequent alteration1 occur far less   
frequently than in the earth's  crust   
generally4 ,hence we are led to conclude
 that the substances which  in the outer
 part of the earth's crust always exist 
in combination  with oxygen1 are at     
greater depths in a free and uncombined 
condition4    ,nor is it a circumstance 
altogether unworthy of attention that   
the  researches of ,mr4 ,norman ,lockyer
 and other astronomers1 based on the    
known facts of the relative densities of

 the several members of the  solar      
system1 and the ascertained relations of
 the different solar  envelopes1 have   
led to conclusions closely in accord    
with those arrived  at by geologists4   
,these researches appear to warrant the 
hypothesis  that the interior of our    
globe consists of metallic substances   
uncombined with oxygen1 and that among  
these metallic substances iron  plays an
 important part4 ,our globe1 as we know1
 is a great magnet1  and the remarkable 
phenomena of terrestrial magnetism may  
also not  improbably find their         
explanation in the fact that metallic   
iron forms  #hj large a portion of the  
earth's interior4    ,the interesting   
facts which we have been considering may
 be made  clearer by the accompanying   
diagram 7fig4 #hh74 ,the materials      
ejected  from volcanic vents 7lavas7 are
 in almost all cases compounds of       
silicon and the various metals with     
oxygen4 ,in the lighter or acid  lavas  
oxygen constitutes one-half of their    

weight1 and the proportion  of metals of
 the iron-group is very small4 ,as we   
pass to the heavier  intermediate and   
basic lavas1 we find the proportion of  
oxygen  diminishing1 and the metals of  
the alkaline earths 7magnesium and      
calcium7 with the metals of the         
iron-group increasing1 in quantity4 ,in 
the small and interesting group of the  
ultra-basic lavas the proportion  of    
oxygen is comparatively small1 and the  
proportion of magnesium and  iron very  
high4 ,so much for the terrestrial      
rocks4    ,illustration3 ,fig4          
#hh4--;,diagram illustrating the        
relation between the  ,terrestrial and  
the ,extra-,terrestrial ,rock4          
,sidenote3 ,,terrestrial ,,and          
,,extra-,,terrestrial ,,rocks4    ,now  
let us turn our attention to the        
extra-terrestrial rocks or those  found 
in meteorites4 ,the ,asiderites are     
quite identical in composition  with the
 ultra-basic lavas of our globe1 but in 
the ,sporadosiderites  and the          

,syssiderites we find the proportion of 
oxygen rapidly  diminishing1 and that of
 metallic iron increasing4 ,finally1 in 
the  ,holosiderites the oxygen entirely 
disappears1 and the whole mass  becomes 
metallic4    ,from the ,holosiderites at
 one end of the chain to the add lavas  
at the other1 we find there is a        
complete and continuous series2  the    
rocks of terrestrial origin overlapping1
 in their least  oxydized               
representatives1 the most highly        
oxydized representatives  of the        
extra-terrestrial rocks4 ,but the       
discovery at ,ovifak of  the            
iron-masses1 and the basalts with iron  
disseminated1 has  afforded another very
 important link1 placing the terrestrial
 and  extra-terrestrial rocks in closer 
relations with one another4    ,all     
these facts appear to point to the      
conclusion that the earth's  interior   
consists of metallic substances either  
quite uncombined  or simply alloyed with
 one another1 and among these iron is   

very  conspicuous by its abundance4 ,the
 outer crust1 which is probably of no   
great thickness1 contains an enormous   
proportion of oxygen and silicon        
combined with the materials which       
constitute the interior portions of  our
 globe4 ,it may be1 as has been         
suggested by astronomers1 that our      
earth consisted at one time of a solid  
metallic mass surrounded by a  vaporous 
envelope of metalloids1 and that the    
whole of the latter1 with  the exception
 of the constituents of the atmosphere  
and ocean1 have  gradually entered into 
combination with the metals of the      
nucleus to  form the existing crust of  
the globe4 ,but of this period the      
geologist  can take no cognisance4 ,the 
records which he studies evidently      
commenced at a long subsequent period1  
when the conditions prevailing  at the  
earth's surface differed but little1 if 
at all1 from those which  exist at the  
present day4 ,equally little has the    
geologist to do with  speculations      

concerning a far distant future when1 as
 some philosophers  have suggested1 the 
work of combination of the waters and   
atmosphere of  the earth's surface with 
the metallic substances of its interior 
shall  be completed1 and our globe1     
entirely deprived of its fluid          
envelopes1  reduced to the condition in 
which we find our satellite1 the moon4  
99       99       99       99       99  
,sidenote3 ,,physical ,,condition ,,of  
,,earth',s ,,interior4    ,there is     
another class of enquiries concerning   
the earth's interior to  which the      
attention of both geologists and        
astronomers has long been               
directed--that1 namely1 which deals with
 the problem of the physical  condition 
of the interior of our globe4    ,the   
fact that masses of molten materials are
 seen at many points of the  earth's    
surface to issue from figures in the    
crust of our globe1 seems  at first     
sight to find a simple explanation if we
 suppose our planet  to consist of a    

fluid central mass surrounded by a solid
 crust4 ,hence  we find that among those
 who first thought upon this subject1   
this  hypothesis of a liquid centre and 
a solid crust was almost universally    
accepted4 ,this hypothesis was supposed 
to find further support in the  fact    
that1 as we penetrate into the earth's  
crust by mines or boring  operations1   
the temperature is found to continually 
increase4 ,it was  imagined1 too1 that  
this condition of our planet would best 
agree with  the requirements of the     
nebular hypothesis of ,laplace1 which   
explains  the formations and movements  
of the bodies of the solar system by the
  cooling down of a nebulous mass4      
,but a more careful and critical        
examination of the question has led     
many geologists and astronomers to      
reject the hypothesis that the earth    
consists of a great fluid mass          
surrounded by a comparatively thin shell
  of solid materials4    ,volcanic      
outbursts and earthquake tremors1 though

 so terrible and  destructive to man and
 his works1 are but slight and          
inconsiderable  disturbances in a globe 
of such vast dimensions as that on which
 we  live4 ,the condition of the crust  
of the globe is1 in spite of volcanic   
and earthquake manifestations1 one of   
general stability2 and this  general    
stability has certainly been maintained 
during the vast periods  covered by the 
geological record4 ,such a state of     
things seems quite  irreconcilable with 
the supposition that1 at no great depth 
from the  surface1 the whole mass of the
 globe is in a liquid condition4 ,if1 on
  the other hand1 it be supposed that   
the solid crust of the globe is  several
 hundreds of miles in thickness1 it is  
difficult to understand  how the local  
centres of volcanic activity could be   
supplied from such  deep-seated sources4
    ,there are other facts which seem   
equally irreconcilable with the         
hypothesis of a fluid centre and a thin 
solid crust in our globe4 ,if  all      

igneous products were derived from one  
central reservoir1 we might  fairly     
expect to find a much greater uniformity
 of character among  those products than
 really exists4 ,but in some cases1     
materials of  totally different         
composition are ejected at the same time
 from closely  adjoining volcanic       
districts4 ,thus in ,hungary and        
,bohemia1 as we have  seen1 lavas of    
totally different character were being  
extruded during  the ,miocene period4   
,in the island of ,hawaii1 as ,professor
 ,dana has  pointed out1 igneous        
ejections have taken place at a crater  
#ad1jjj feet  above the sea-level1 while
 a closely adjoining open vent at a     
level  #aj1jjj feet lower exhibited no  
kind of sympathy with the disturbance4  
,whatever may be the cause of volcanic  
action1 it seems clear that it  does not
 originate in a universal mass of       
liquefied material situated  at no great
 depth from the earth's surface4    ,the
 conclusions arrived at by astronomers  

and physicists is one quite  in accord  
with those which geologists have reached
 by totally different  methods4 ,it is  
now very generally admitted that if the 
earth were not  a rigid mass1 its       
behaviour under the attract live        
influences of the  surrounding members  
of the solar system would be very       
different to what  is found to be the   
case4    ,sidenote3 ,,arguments         
,,against ,,liquid ,,interior4    ,that 
the earth is in a solid condition to a  
great depth from the  surface1 and      
possibly quite to the centre1 is a      
conclusion concerning  which there can  
be little doubt2 and in the next chapter
 we shall  endeavour to show that such a
 condition of thirds is by no means     
incompatible with those manifestations  
of internal energy1 the  phenomena of   
which we are considering in this work4  
,the question1  therefore1 of the       
complete solidity of our globe1 or of   
its consisting  of a solid and a liquid 
portion1 is one of speculative interest 

only1  and is in no way involved in our 
investigations concerning the nature    
and origin of volcanic activity4 ,we may
 conclude this chapter by  enumerating  
the several hypotheses which have at    
different times been  maintained        
concerning the nature of the interior of
 our globe4    ,first4 ,it has been     
suggested that the earth consists of a  
fluid or  semi-fluid nucleus surrounded 
and enclosed in a solid shell4 ,some    
have maintained this shell to be of such
 insignificant thickness1 as  compared  
with the bulk of the interior liquid    
mass1 that portions of  the latter are  
able to reach the earth's surface       
through movements  and fractures of the 
outer shell1 and that in this manner    
volcanic  manifestations originate4     
,others1 impressed with the general     
stability  and rigidity of the globe as 
a whole1 have maintained that the outer 
solid shell must have a very            
considerable thickness1 amounting       
probably to not less than several       

hundreds of miles4 ,but through a  shell
 of such thickness it is difficult to   
conceive of the liquid  masses of the   
interior finding their way to the       
surface1 and those who  have held this  
view are driven to suggest some other   
means by which  local developments of   
volcanic action might be brought about4 
,secondly4 ,some physicists have        
asserted that a globe of liquid  matter 
radiating its heat into space1 would    
tend to solidify both at  the surface   
and the centre1 at the same time4 ,the  
consequence of this  action would be the
 production of a sphere with a solid    
external shell  and a solid central     
nucleus1 but with an interposed layer in
 a fluid  or semi-fluid condition4 ,it  
has been pointed out that if we suppose 
the solidification to have gone so far1 
as to have caused the partial  union of 
the interior nucleus and the external   
shell1 we may conceive a  condition of  
things in which the stability and       
rigidity is sufficient  to satisfy both 

geologists and astronomers1 but that in 
still  unsolidified pockets or          
reservoirs1 filled with liquefied rock1 
between  the nucleus and the shell1 we  
should have a competent cause for the   
production of the volcanic phenomena of 
the globe4 ,in this hypothesis1         
however1 it is assumed that the cooling 
at the centre and the surface  of the   
globe would go on at such rates that the
 reservoirs of liquid  material would be
 left at a moderate depth from the      
surface1 so that  easy communication    
could be opened between them and        
volcanic vents4    ,sidenote3 ,,review  
,,of ,,the ,,several ,,hypotheses4      
,thirdly4 ,it has been maintained that  
the earth may have become  perfectly    
solid from the centre to the surface4   
,those who hold this  view endeavour to 
account for the phenomena of volcanoes  
in one of two  ways4 ,it may be1 they   
say1 that the deep-seated rock-masses1  
though  actually solid1 are in a state  
of potential liquidity2 that though     

reduced to a solid state by the intense 
pressure of the superincumbent  masses1 
yet such is the condition of unstable   
equilibrium in the whole  mass1 that the
 comparatively slight movements and     
changes taking place  at the earth's    
surface suffice to bring about the      
liquefaction of  portions of its crust  
and consequent manifestations of        
volcanic energy4  ,but ,it may be1 as   
other supporters of the doctrine of the 
earth's  complete solidity have         
maintained1 that the phenomena of       
volcanoes  have no direct connection    
with a supposed incandescent condition  
of  our planet at all1 and that there   
are chemical and mechanical forces  at  
work within our globe which are quite   
competent to produce at the  surface all
 those remarkable phenomena which we    
identify with volcanic  action4    ,from
 this summary of the speculative views  
which have been entertained  upon the   
subject of the physical condition of the
 earth's interior1  it will be clear    

that at present we have not sufficient  
evidence for  arriving at anything like 
a definite solution of the problem4 ,the
  conditions of temperature and pressure
 which exist in the interior of  a globe
 of such vast dimensions as our earth1  
are so far removed from  those which we 
can imitate in our experimental         
enquiries1 and it is so  unsafe to push 
the application of laws arrived at by   
the latter to the  extreme limits       
required by the former1 that we shall do
 well to pause  before attempting to    
dogmatise on such a difficult question4 
,in the next chapter we shall endeavour 
to grapple with a somewhat more  hopeful
 task1 to point out how far observation 
and experiment have  enabled us to offer
 a reasonable explanation of the        
wonderful series of  phenomena which are
 displayed during outbursts of volcanic 
activity4          ,,chapter ,,xii4     
,,the ,,attempts ,,which ,,have ,,been  
,,made ,,to ,,explain ,,the ,,causes    
,,of ,,volcanic  ,,action4      ,every  

completed scientific investigation must 
consist of four series  of operations4  
,in the first of these an attempt is    
made to collect the  whole of the facts 
bearing on the question1 by means of    
observation  and experiment2 the latter 
being only observation under conditions 
determined by ourselves4 ,in the second 
stage of the enquiry1 the  attention is 
directed to classifying and grouping the
 isolated facts1  so as to determine    
their bearings upon one another1 and the
 general  conclusions to which they     
appear to point4 ,in the third stage1 it
 is  sought to frame an hypothesis which
 shall embrace all the observed  facts1 
and shall be in harmony with the general
 conclusions derived  from them4 ,in the
 fourth stage1 this hypothesis is put to
 the most  rigid test2 comparing the    
results which must follow1 if it be     
true1  with the phenomena actually      
observed1 and rejecting or amending our 
hypothesis accordingly4 ,every great    
scientific theory has thus been         

established by these four               
processes--observation1 generalisation1 
hypothesis1 and verification4    ,the   
enquiry concerning the nature and causes
 of volcanic action is far  from being a
 completed one4 ,it is true that many   
hypotheses upon the  subject have been  
framed1 but in too many instances these 
have not been  based on accurate        
observations and careful                
generalisations1 and can be  regarded as
 little better than mere guesses4       
,indeed1 the state of the  enquiry at   
the present time would seem to be as    
follows4 ,although much  remains to be  
done in the direction both of           
observation and experiment1  the main   
facts of the case have been established 
upon irrefragable  evidence4 ,the       
classification and comparison of these  
facts have led to  the recognition of   
certain laws1 which seem to embrace all 
the known  facts4 ,to account for these 
facts and their demonstrated relations  
to  one another1 certain tentative      

hypotheses have been suggested2 but in  
no case can it be truly said that these 
latter have so far stood the  test of   
exact enquiry as to deserve to rank as  
demonstrated truths4 ,a  complete and   
consistent theory of volcanic action    
still remains to be  discovered4        
,sidenote3 ,,value ,,and ,,limits ,,of  
,,hypotheses4    ,in accordance with the
 plan which we have sketched out for    
ourselves  at the commencement of this  
work1 we shall aim at following what has
  been the order of investigation and   
discovery in our study of volcanic      
action2 and in this concluding chapter  
we shall indicate the different         
hypotheses by which it has been proposed
 to account for the varied  phenomena1  
which we have discussed in the preceding
 pages1 and their  remarkable relations 
to one another4 ,we shall endeavour1 in 
passing1  to indicate how far these     
several hypotheses appear to be         
probable1  as satisfying a larger or    
smaller number of those conditions of   

the  problem which have been established
 by observation1 experiment1 and        
careful reasoning2 but we shall at the  
same time carefully avoid such  advocacy
 of any particular views as would tend  
to a prejudgment of  the question4      
,hypothesis is1 as we have seen1 one of 
the legitimate  and necessary operations
 in scientific investigation4 ,it only  
becomes  a dangerous and treacherous    
weapon when it is made to precede rather
  than to follow observation and        
experiment1 or when being regarded  with
 paternal indulgence1 an attempt is made
 to shield it from the  relentless logic
 of facts4 ,good and bad hypotheses must
 be allowed to  'grow together till the 
harvest2' such as are unable to         
accommodate  themselves to the          
surrounding conditions imposed by       
newly-discovered  facts and             
freshly-established laws will assuredly 
perish2 and in this  'struggle for      
existence' the true hypothesis will in  
the end survive1  while the false ones  

perish4    ,it may well happen1 however1
 that among the hypotheses which have up
 to  the present time been framed1 none 
will be found to entirely satisfy  all  
the conditions of the problem4 ,new     
discoveries in physics and  chemistry   
have suggested fresh explanations of    
volcanic phenomena in  the past1 and may
 continue to do so in the future2 and   
the true theory  of volcanic action1    
when it is at last discovered1 may      
combine many of  the principles which   
now seem to be peculiar to different    
hypotheses4    ,let us1 in the first    
place1 enquire what are the facts which 
must be  accounted for in any theory of 
volcanic action4 ,we have already been  
led to the conclusion that the phenomena
 exhibited by volcanoes were  entirely  
produced by the escape of imprisoned    
water and other gases  from masses of   
incandescent and fluid rock4 ,our       
subsequent examination  of the problem  
confirmed the conclusion that in all    
cases of volcanic  outburst we have     

molten rock-materials from which water  
and other  gases issue with greater or  
less violence4 ,the two great facts to  
be accounted for1 then1 in any attempted
 explanation of volcanic  phenomena1 are
 the existence of this high temperature 
at certain points  within the earth's   
crust1 and the presence of great        
quantities of water  and gas1 imprisoned
 in the rocks4 ,we shall perhaps        
simplify the enquiry  if we examine     
these two questions separately1 and1 in 
the first place1  review those          
hypotheses which have been suggested to 
account for high  temperatures in the   
subterranean regions1 and1 in the second
 place1  examine those which seek to    
explain the presence of large quantities
 of  imprisoned water and gases4        
,sidenote3 ,,increase ,,of ,,temperature
 ,,with ,,depth4    ,that a high        
temperature exists in the earth's crust 
at some depth from  the surface is a act
 which does not admit of any doubt4     
,every shaft  sunk for mining           

operations1 and every deep boring made  
for the purpose  of obtaining water1    
proves that a more or less regular      
increase of  temperature takes place as 
we penetrate downwards4 ,the average    
rate  of this increase of temperature   
has been estimated to be about #a       
,fahrenheit for every #ej or #fj feet of
 depth4    ,now if it be assumed that   
this regular increase of temperature    
continues to great depths1 a simple     
calculation proves that at a depth  of  
#i1jjj feet a temperature of #bab       
,fahrenheit will be found--one          
sufficient to boil water at the earth's 
surface--while at a depth of #bh  miles 
the temperature will be high enough to  
melt cast-iron1 and at #cd  miles to    
fuse platinum4    ,so marked is this    
steady increase of temperature as we go 
downwards1  that it has been seriously  
proposed to make very deep borings in   
order  to obtain supplies of warm water 
for heating our towns4 ,arago and       
,walferdin suggested this method for    

warming the ,jardin des ,plantes at     
,paris2 and now that such important     
improvements have been devised in       
carrying borings to enormous depths1 the
 time may not be far distant  when we   
shall draw extensively upon these       
supplies of subterranean  heat4 ,at the 
present time the city of ,buda-,pesth is
 extensively  supplied with hot-water   
from an underground source4 ,should our 
coal-supply ever fail it may be well to 
remember that we have these             
inexhaustible supplies of heat          
everywhere beneath our feet4    ,but    
although we may conclude that at the    
moderate depths we have  indicated such 
high temperatures exist1 it would not be
 safe to  infer1 as some have done1 that
 at a distance of only #dj or #ej miles 
from the surface the materials composing
 our globe are in a state  of actual    
fusion4 ,both theory and experiment     
indicate that under  increased pressure 
the fusing point of solid bodies is     
raised2 and  just as in a ,papin's      

digester we may have water retained by  
high  pressure in a liquid condition at 
a temperature far above #bab ,f41  so in
 the interior of the earth1 masses of   
rock may exist in a solid  state1 at a  
temperature far above that at which they
 would fuse at  the earth's surface4 ,we
 may speak of such rock-masses1 retained
 in a  solid condition by intense       
pressure1 at a temperature far above    
their  fusing point at the earth's      
surface1 as being in a 'potentially     
liquid  condition4' ,upon any relief of 
pressure such masses would at once      
assume the liquid state1 just as the    
superheated water in a ,papin's         
digester immediately flashes into steam 
upon the fracture of the strong  vessel 
by which it is confined4 ,we have       
already seen how the action  at volcanic
 vents often appears to indicate just   
such a manifestation  of elastic forces1
 as would be exhibited by the relief of 
superheated  masses from a state of     
confinement by pressure4    ,in         

reasoning upon questions of this kind1  
however1 we must always be  upon our    
guard against giving undue extension to 
principles and laws  which seem to be   
clearly established by experiment at the
 earth's  surface4 ,it is well to       
remember how exceedingly limited is our 
command  of extreme pressures and high  
temperatures1 when compared with those  
which may exist within a body of the    
dimensions of our globe4    ,sidenote3  
,,effect ,,of ,,pressure ,,on           
,,fusion-,,point4    ,if we were to     
imagine a set of intelligent creatures1 
who were able to  command only a range  
of temperatures from #ej to #bjj ,f41   
engaged upon  an investigation of the   
properties of water1 we shall easily    
understand  how unsafe it may be to     
extend generalisations far beyond the   
limits  covered by actual experiment4   
,such beings1 from their observation of 
the regular changes of volume of water  
at all the temperatures they  could     
command1 might infer that at still      

higher and lower temperatures  the same 
rates of expansion and contraction would
 be maintained4 ,yet1  as we well know1 
such an inference would be quite wide of
 the truth2  for a little above #bjj ,f4
 water suddenly expands to #a1gjj times 
its  volume1 and not far below #ej ,f4  
the contraction is suddenly changed  for
 expansion4    ,it has been argued by   
the late ,mr4 ,david ,forbes and others 
that1  inasmuch as experiment has shown 
that--though the fusing points of       
solids are raised by pressure1 yet that 
this rise of the fusing  points goes on 
in a diminishing ratio as compared with 
the pressures  applied--a limit will    
probably be reached at which the most   
intense  pressure will not be sufficient
 to retain substances at a high         
temperature in their solid state4 ,the  
fact that gases cannot be  retained in a
 liquid condition by the most intense   
pressure at a  temperature above their  
critical point1 may seem by analogy to  
favour  the same conclusion4 ,hence1    

,david ,forbes1 ,dana1 and other        
authors1 have  argued in favour of the  
existence of a great liquid nucleus in  
our  globe covered by a comparatively   
thin1 solid crust4 ,and if we accept    
the supposed proofs of a constant       
increase of temperature from the        
surface to the centre of the globe1 such
 a conclusion appears to be at  least as
 well founded as that which regards the 
central masses of the  earth as         
maintained in a solid condition by      
intense pressure4    ,a little          
consideration will1 however1 convince us
 that the facts which  have been relied 
upon as proving the intensely heated    
condition of the  central masses of our 
globe1 are by no means so conclusive as 
has been  supposed4    ,the earth's     
form1 which mathematicians have shown to
 be exactly that  which would be        
acquired by a globe composed of yielding
 materials  rotating on its axis at the 
rate which our planet does1 has often   
been adduced as proving that the latter 

was not always in a rigid and           
unyielding condition4 ,in the same way1 
all the remarkable facts and  relations 
of the bodies of the solar system1 which
 have been shown by  astronomers to lend
 such support to the nebular hypothesis1
 have been  thought1 at the same time1  
to favour the view that our earth is    
still  in a condition of uncompleted    
solidification4    ,but it is quite     
admissible to accept the nebular        
hypothesis and the  view that our globe 
attained its present form while still in
 a state  of fluidity1 and at the same  
time to maintain that our earth has long
  since reached its condition of        
complete solidification4 ,and there are 
not a few facts which appear to lend    
support to such a conclusion4           
,sidenote3 ,,supposed ,,proofs ,,of     
,,liquid ,,nucleus4    ,if the rapid    
rate of increase in temperature which   
has been  demonstrated to occur at so   
many parts of the earth's surface be    
maintained to the centre1 then1 as      

argued by ,david ,forbes and ,dana1 it  
is difficult to conceive of our earth as
 being in any other condition  than that
 of a liquid mass covered by a          
comparatively thin crust4 ,the          
objection to this view1 both upon       
geological and astronomical grounds1  we
 have pointed out in the previous       
chapter4    ,before accepting as a      
demonstrated conclusion this notion of a
 constant  increase of temperature from 
the surface to the centre of our globe1 
it  may be well to re-examine the facts 
which are relied upon as proving it4    
,that there is a general increase of    
temperature so far as we are able  to go
 downwards in the earth's crust1 there  
can1 as we have seen1  be no doubt      
whatever4 ,yet it may be well to bear in
 mind how very  limited is the range of 
our observation on the subject4 ,the    
deepest  mines extend to little more    
than half-a-mile from the surface1 and  
the  deepest borings to little more than
 three-quarters of a mile1 while the    

distance from the earth's surface to its
 centre is nearly #d1jjj miles4  ,we may
 well pause before we extend            
conclusions1 derived from such very     
limited observations1 to such enormous  
depths4    ,but when we examine         
critically these observations           
themselves1 we  shall find equal grounds
 for caution in generalising from them4 
,there  is the greatest and most        
startling divergence in the results of  
the  observations which have been made  
at different points at the earth's      
surface4 ,even when every allowance is  
made for errors of observation1  these  
discrepancies still remain4 ,in some    
places the increase of  temperature as  
we go downwards is so rapid that it     
amounts to #a  ,fahrenheit for every #bj
 feet in depth1 while in other cases1 in
 order  to obtain the same increase in  
temperature of #a ,fahrenheit1 we have  
to  descend as much as #ajj feet4       
,now if1 as is so often assumed1 this   
increase of temperature as we  go       

downwards be due to our approach to     
incandescent masses forming  the        
interior portions of the globe1 it is   
difficult to understand  why greater    
uniformity is not exhibited in the rate 
of increase in  different areas4 ,no    
difference in the conducting powers of  
the various  rock-materials is          
sufficient to account for the fact that 
in some  places the rate of increase in 
temperature in going downwards is no    
less than five times as great as it is  
in others4    ,sidenote3 ,,variations   
,,in ,,underground ,,temperatures4      
,again1 there are some remarkable facts 
concerning the variation in  the rate of
 increase in temperature with depth     
which seem equally  irreconcilable with 
the theory that the heat in question is 
directly  derived from a great1 central1
 incandescent mass4 ,m4 ,walferdin1 by a
  series of careful observations in two 
shafts at ,creuzot1 proved that  down to
 the depth of #a1hjj feet the increase  
of temperature amounted to  #a          

,fahrenheit for every #ee feet of       
descent1 but below the depth named1  the
 rate of increase was as much as #a     
,fahrenheit for every #dd feet4 ,on  the
 other hand1 in the great boring of     
,grenelle at ,paris1 the increase  in   
temperature down to the depth of #gdj   
feet amounted to #a ,fahrenheit  for    
every #ej feet of descent1 but from #gdj
 feet down to #a1fjj feet1  the rate of 
increase diminished to #a for #ge feet  
of descent4 ,the  same remarkable fact  
was strikingly shown in the case of the 
deepest  boring in the world--that of   
,sperenberg1 near ,berlin1 which        
attained  the great depth of #d1jeb     
feet4 ,in this case1 the rate of        
increase in  temperature for the first  
#a1ijj feet1 was #a ,fahrenheit for     
every #ee  feet of descent1 and for the 
next #b1jjj1 it diminished to #a        
,fahrenheit  for every #fb feet of      
descent4 ,in the deep well of           
,buda-,pesth there was  actually found a
 decline in temperature below the depth 

of #c1jjj feet4    ,perhaps the most    
interesting fact in connection with this
 question  which has been discovered of 
late years1 is that in districts which  
have recently been the seat of volcanic 
agencies1 the rate of increase  in      
temperature1 as we go downwards in the  
earth's crust1 is abnormally  high4     
,thus at ,monte ,massi in ,tuscany1 the 
temperature was found to  increase at   
the rate of #a ,fahrenheit for every #bd
 feet of descent4  ,in ,hungary several 
deep wells and borings have been made1  
which prove  that a very rapid increase 
of temperature occurs4 ,the deep boring 
at  ,buda-,pesth penetrates to a depth  
of #c1afj feet1 and a temperature of    
#agh ,fahrenheit has been observed near 
the bottom4 ,the rate of increase  of   
temperature in this boring was about #a 
for every #bc feet of  descent4 ,in the 
mines opened in the great ,comstock     
lode1 in the western  territories of the
 ,united ,states1 an abnormally high    
temperature has  been met with amounting

 in some cases to #aeg ,fahrenheit4     
,although  this is the richest          
mineral-vein in the world1 having       
yielded since  #ahei1 when it was first 
discovered1 #fj1jjj1jjjl4 worth of gold 
and  silver1 this rapid increase in     
temperature in going downwards threatens
  in the end to entirely baffle the     
enterprise of the miner4 ,the rate  of  
increase in temperature in the case of  
the ,comstock mines has been  estimated 
at #a ,fahrenheit for every #df feet of 
descent1 between #a1jjj  and #b1jjj feet
 from the surface1 but as much as #a    
,fahrenheit for every  #be feet1 at     
depths below #b1jjj feet4    ,the facts 
which we have stated1 with others of a  
similar kind1 have  led geologists to   
look with grave feelings of doubt upon  
the old  hypothesis which regarded the  
increase of temperature found in making 
excavations into the earth's crust as a 
proof that we are approaching a  great  
incandescent nucleus4 ,they have thus   
been led to enquire whether  there are  

any conceivable sources of high         
temperatures at moderate                
depths--temperatures which would be     
quite competent to produce locally  all 
the phenomena of volcanic action4       
,there are not wanting other facts which
 seem to point to the same  conclusion3 
namely1 that volcanic action is not due 
to the existence  of a universal        
reservoir of incandescent material      
occupying the central  portion of our   
globe1 but to the local development of  
high temperatures  at moderate depths   
from the surface4    ,sidenote3 ,,depths
 ,,at ,,which ,,earthquakes ,,originate4
    ,the close connection between the   
phenomena of volcanoes and earthquakes  
cannot be doubted4 ,it is true that some
 of those vibrations or tremors  of the 
earth's crust1 to which we apply the    
name of earthquakes1  occur in areas    
which are not now the seat of volcanic  
action2 and it  is equally true that the
 stratified rock-masses of our globe1   
far  away from any volcanic centres1    

exhibit proofs of violent movement  and 
fracture1 in the production of which1   
concussions giving rise  to earthquake  
vibrations1 could scarcely fail to have 
occurred4 ,but  it is none the less     
certain that earthquakes as a rule take 
place  in those areas which are the     
seats of volcanic action1 and that      
great earthquake-shocks precede and     
accompany volcanic outbursts4           
,sometimes1 too1 it has been noticed    
that the manifestation of  activity at a
 volcanic centre is marked by the sudden
 decline of the  earthquake-tremors of  
the district around1 as though a        
safety-valve had  been opened at that   
part of the earth's surface4    ,mr4    
,mallet has shown that by the careful   
study of the effects  produced at the   
surface by earthquake-vibrations1 we may
 determine  with considerable accuracy  
the point at which the shock or         
concussion  occurred which gave rise to 
the vibration4 ,now it is a most        
remarkable  fact that such calculations 

have led to the conclusion that1 so far 
as is at present known1 earthquake      
shocks never originate at greater       
depths than thirty miles from the       
surface1 and that in some cases  the    
focus from which the waves of elastic   
compression producing an  earthquake    
proceed is only at the depth of seven or
 eight miles4  ,as we have already seen1
 there can be no doubt that in the great
  majority of instances the forces      
originating earthquake-vibrations and   
volcanic outbursts are the same1 and    
independent lines of reasoning  have    
conducted us to the conclusion that     
these forces operate at very  moderate  
distances from the earth's surface4     
,under these circumstances1 geologists  
have been led to enquire  whether there 
are any means by which we can conceive  
of such an  amount of heat1 as would be 
competent to produce volcanic outbursts1
  being locally developed at certain    
points within the earth's crust4        
,recent discoveries in physical science 

which have shown the close  relation to 
one another of different kinds of force1
 and their mutual  convertibility1 have 
at least suggested the possibility of   
the  existence of causes by which such  
high temperatures within certain        
portions of the earth's crust may be    
originated4    ,sidenote3 ,,davy',s     
,,chemical ,,theory4    ,when1 at the   
commencement of the present century1    
,sir ,humphry ,davy  discovered the     
remarkable metals of the alkalies and   
alkaline earths1  and at the same time  
demonstrated the striking phenomena     
which are  exhibited if these metals be 
permitted to unite with oxygen1 he at   
once perceived that if such metals      
existed in an uncombined condition      
within the earth's crust1 the access of 
water and air to the mass might  give   
rise to the development of such an      
amount of heat1 as would be  competent  
to produce volcanic phenomena at the    
surface4 ,it is true that  at a later   
date ,davy recognised the chemical      

theory of volcanoes as  being beset with
 considerable difficulties1 and was     
disposed to abandon  it altogether4 ,it 
was argued1 with considerable show of   
reason1 that if  the heat at volcanic   
centres were produced by the access of  
water to  metallic substances1 great    
quantities of hydrogen would necessarily
 be  evolved1 and this gas ought to be  
found in prodigious quantities among    
the emanations of volcanoes4 ,the fact  
that such enormous quantities of        
hydrogen gas are not emitted from       
volcanic vents has been held by many    
authors to be fatal to the chemical     
theory of volcanoes4    ,but the later  
researches of ,graham and others have   
made known facts  which go far towards  
supplying an answer to the objections   
raised  against the chemical theory of  
volcanoes4 ,various solids and liquids  
have been shown to possess the power of 
absorbing many times their  volume of   
certain gases4 ,among the gases thus    
absorbed in large  quantities by solids 

and liquids1 hydrogen is very           
conspicuous4 ,in  some cases gases are  
absorbed by metals or other solids in a 
state of  fusion1 and yielded up again  
by them as they cool4    ,it is a very  
remarkable circumstance that some       
meteorites are found  to have absorbed  
large quantities of hydrogen gas1 and   
this is given  off when they are heated 
in vacuo4 ,thus it has been demonstrated
 that  certain meteorites have contained
 as much as forty seven times their  own
 volume of hydrogen gas4    ,we have    
already pointed out that there are      
reasons for believing the  internal     
portions of our globe to be composed of 
materials similar to  those found in    
meteorites4 ,if such be the case1 the   
access of water  to these metallic      
substances may result in the formation  
of oxides1  attended with a great local 
development of heat1 the hydrogen which 
is liberated being at once absorbed by  
the surrounding metallic  substances4   
,that this oxidation of the metallic    

substances in the  interior of our globe
 by the access of water and air from the
 surface  is continually going on1 can  
scarcely be doubted4 ,we may even look  
forward to a far-distant period when the
 whole of the liquid and  gaseous       
envelopes of the globe shall have been  
absorbed into its  substance1 and our   
earth thereby reduced to the condition  
in which we  now find the moon to be4   
,there is a second method by which high 
temperatures might be locally  developed
 within the earth's crust1 which has    
been suggested by ,vose1  ,mallet1 and  
other authors4    ,we have good grounds 
for believing that the temperature of   
our globe  is continually diminishing by
 its radiation of heat into space4 ,this
  cooling of our globe is attended by   
contraction1 which results in  movements
 of portions of its crust4 ,it may at   
first sight appear that  such movements 
would be so small and insignificant as  
to be quite  unworthy of notice4 ,but if
 we take into account the vast size of  

our  earth it will be seen that the     
movements of such enormous masses may be
  attended with the most wonderful      
results4    ,it has been shown that if a
 part of the earth's crust fifty miles  
in  thickness were to have its          
temperature raised #bjj ,fahrenheit1 its
  surface would be raised to the extent 
of #a1jjj or #a1ejj feet ,le ,conte  has
 pointed out that if we conceive the    
conduction of heat to take  place at    
slightly different rates along different
 radii of our globe1  we should at once 
be able to account for the existing     
inequalities of  the earth's surface1   
and for all those continental movements 
which can  be shown to have taken place 
in past geological periods4             
,sidenote3 ,,dynamical ,,theories4      
,but if we admit1 as we have good       
grounds for doing1 that the loss of     
heat from the external portions of our  
globe goes on more rapidly than  in the 
case of the central masses1 we have     
thereby introduced another  powerful    

agent for the production of high        
temperatures within the  earth's crust4 
,the external shell of the globe will   
tend to contract  upon the central mass1
 and in so doing a series of tangential 
strains  will result which will be      
capable of folding and crumpling the    
rocks  along any lines of weakness4     
,that such crushing and crumpling has   
during all geological periods taken     
place along lines of weakness  in the   
earth's crust1 is proved1 as we have    
seen1 by the phenomena  presented by    
mountain-ranges4 ,now these crushings1  
crumplings1 and  other violent movements
 of great rock-masses must result in the
  development of a vast amount of heat1 
just as the forcing down of a  break    
upon a moving wheel produces heat4 ,this
 conclusion is strikingly  confirmed by 
the well-known geological fact that     
nearly all rocks which  have undergone  
great movement and contortion are found 
to present  evidence of having been     
subjected to such chemical and          

crystalline  actions1 as would result   
from the development of a high          
temperature  within their mass4         
,sidenote3 ,,recapitulation ,,of        
,,several ,,theories4    ,let us sum up 
briefly the various methods which have  
been suggested to  account for the high 
temperatures within certain parts of the
 earth's  crust by which volcanic       
phenomena are produced4    ,our globe   
may be conceived of as an incandescent  
liquid mass surrounded  by a cooler1    
solid shell4 ,if we regard this liquid  
interior mass as  supplying directly the
 various volcanic vents of the earth1 it
 must be  conceded that the outer shell 
is of comparatively slight thickness4   
,but astronomers are almost universally 
agreed that such a thin outer  shell and
 inner liquid mass are quite            
incompatible with that rigidity  which  
our planet exhibits under the           
attractions of its neighbours4          
,geologists are almost equally unanimous
 in regarding this hypothesis  of a     

liquid nucleus and thin1 solid shell as 
contradicted by the  stability of the   
conditions which have been maintained   
during such  long past periods1 and     
which exist at the present day4 ,the    
extent and  character of volcanic action
 do not indicate a condition of general 
instability in our earth1 but one of    
stability subject to small and  local   
interferences ,the grandest volcanic    
disturbances appear small and           
insignificant1 if we take into account  
the vast dimensions of the globe  upon  
which they are displayed4    ,if1 on the
 other hand1 we consider the outer solid
 shell to be of  great thickness1 we are
 met by the difficulty of accounting for
 the  upheaval of liquid matter through 
such vast thicknesses of a solid  shell4
 ,the differences in character of lavas 
extruded from closely  adjoining        
volcanic districts seem equally         
difficult of explanation on  any theory 
of a central1 fluid nucleus and a solid1
 outer shell4 ,nor is  the distribution 

of heat within the earth's crust so     
uniform as might  be anticipated1 if the
 source of that heat be a great central 
mass of  highly heated materials4       
,under these circumstances1 geologists  
and physicists have enquired  whether   
any other conditions can be imagined as 
existing in the earth's  interior1 which
 would better account for the observed  
phenomena than  does the hypothesis of a
 liquid nucleus and a solid outer shell4
 ,two  such alternative hypotheses have 
been suggested4    ,mr4 ,hopkins1       
adopting the theory that the earth has  
solidified both at  the centre and its  
outer surface1 endeavoured to explain   
the occurrence  of volcanoes and        
earthquakes by supposing that cavities  
of liquid  material have been left      
between the solid nucleus and the solid 
shell1  and these cavities full of      
liquid material constitute the sources  
from  which the existing volcanoes of   
the globe draw their supplies4 ,but     
this hypothesis is found to be beset    

with many difficulties when we  attempt 
to apply it to the explanation of the   
phenomena of volcanic  action4 ,it      
entirely fails1 among other things1 to  
account for the  remarkable fact that   
during past geological periods the scene
 of  volcanic action has been           
continually shifting over the surface of
 the  earth1 so that there is probably  
no considerable area of our globe  which
 has not at one time or other been      
invaded by the volcanic forces4    ,by  
some other theorists1 who have felt the 
full force of this last  objection1 an  
attempt has been made to explain the    
phenomena of  volcanoes by supposing    
that the globe is solid from its surface
 to its  centre1 but that the internal  
portions of the globe are at such a high
  temperature that they are only        
retained in a solid condition by the    
enormous pressure to which they are     
subjected4 ,the central masses of  the  
globe are thus regarded as being in an  
actually solid1 but in a  potentially   

liquid condition1 and any local relief  
of pressure is at  once followed by the 
conversion of solid to liquefied        
materials1 in the  district where the   
relief takes place1 resulting in the    
manifestation  of volcanic phenomena at 
the spot4 ,it may be granted that this  
hypothesis better accords with the known
 facts of ,vulcanology than any  of     
those which we have previously          
described1 but it is impossible to  shut
 our eyes to the fact that not a few    
serious difficulties still  remain4     
,thus it is based upon the assumption   
that the law of the  elevation of the   
point of fusion by pressure is true at  
temperatures  and pressures almost      
infinitely above those at which we are  
able to  conduct observations2 but      
neither experiment nor analogy warrant  
this  conclusion1 for the former shows  
that the elevation of the point of      
fusion by pressure goes on in a         
continually diminishing ratio1 and the  
latter famishes us with the example of  

volatile liquids which1 above  their    
critical points1 obstinately remain in a
 gaseous condition under  the highest   
pressures4 ,nor is it easy upon this    
hypothesis to account  for the very     
irregular distribution of temperatures  
within the earth's  crust1 as           
demonstrated by observations in mines1  
wells1 and borings4  ,the hypothesis    
further requires the assumption that1 at
 such very  moderate depths as are      
required for the reservoirs of          
volcanoes1 the  effects of pressure and 
temperature on the condition of         
rock-materials  are so nicely balanced  
that the smallest changes at the surface
 lead to  a disturbance of the          
equilibrium4    ,sidenote3              
,,difficulties ,,not ,,yet ,,explained4 
,it is the weight of these several      
objections that has led geologists  in  
recent years to regard with greater     
favour those hypotheses which  seek to  
account for the production of high      
temperatures within parts of  the       

earth's crust1 without having recourse  
to a supposed incandescent  nucleus4 ,if
 it can be shown that there are any     
chemical or mechanical  forces at work  
within the crust of the globe which are 
capable of  producing local elevations  
of temperature1 then we may conceive of 
a  condition of things existing in the  
earth's interior which is free  from the
 objections raised by the astronomer on 
the score of the  earth's proved        
rigidity1 and by the geologist on the   
ground of its  general stability1 and   
which at the same time seems to         
harmonise better  with the observed     
facts of the distribution of temperature
 within the  earth's crust4 ,how far the
 existence of such chemical and         
mechanical  agencies capable of         
producing high temperatures within the  
crust of the  globe have been           
substantiated1 we have already          
endeavoured to point out4    ,it must be
 admitted1 then1 that the questions of  
the nature of the  earth's interior and 

the cause of the high temperatures which
 produce  volcanic phenomena1 are still 
open ones4 ,we have not yet got beyond  
the  stage of endeavouring to account   
for the facts observed by means of      
tentative hypotheses4 ,some of these1 as
 we have seen1 agree with the  facts1 so
 far as they are at present known1 much 
better than others2  but the decision   
between them or the rejection of the    
whole of them in  favour of some new    
hypothesis1 must depend on the results  
of future  observation and enquiry4     
,it may be well1 before leaving this    
subject1 to remark that they are  all   
equally reconcilable with the nebular   
theory of ,kant and ,laplace4  ,granting
 that the matter composing our globe has
 passed successively  through the       
gaseous and liquid conditions1 it is    
open to us to imagine  the earth as now 
composed of a liquid nucleus with either
 a thick or  a thin solid shell2 of a   
solid nucleus and a solid shell with    
more or  less liquid matter between     

them2 or1 lastly1 to conceive of it as  
having become perfectly solid from the  
centre to the surface4    ,sidenote3    
,,cause ,,of ,,the ,,presence ,,of      
,,water ,,in ,,lavas4    ,but it is not 
upon the existence of a high temperature
 within certain  parts of the earth's   
crust that the production of volcanic   
activity  alone depends4 ,the presence  
of water and other liquid and gaseous   
substances in a state of the most       
intimate admixture with the fused       
rock-masses1 is1 as we have seen1 the   
main cause of the violent  displays of  
energy exhibited at volcanic centres4   
,and ,we shall now  proceed to notice   
the hypotheses which have been suggested
 to account  for the presence of these  
liquid and gaseous bodies in the midst  
of the  masses of incandescent materials
 poured out from volcanic vents4        
,there is an explanation of this        
presence of water and various gases in  
the masses of molten rock-materials     
within the earth's crust which at  once 

suggests itself1 and which was formerly 
very generally accepted4  ,volcanoes1 as
 we have seen1 are usually situated near
 coast-lines1 and  if we imagine        
fissures to be produced by which        
sea-water finds access  to masses of    
incandescent rock-materials1 then we can
 regard volcanic  outbursts as resulting
 from this meeting of water with        
rock-masses in a  highly healed         
condition4 ,this supposition has been   
thought to receive  much support from   
the fact that many of the gases evolved 
from volcanic  vents are such as would  
be produced by the decomposition of     
substances  present in sea-water4       
,but it frequently happens that an      
explanation which at first sight        
appears to be very simple and obvious1  
turns out on more critical  examination 
to be quite the reverse1 and this is the
 case with the  supposed origination of 
volcanic outbursts by the access of     
sea-water  to incandescent rock-material
 by means of earth-fissures4 ,it is     

difficult to understand how1 by such    
means1 that wonderfully intimate  union 
between the liquefied rock and the      
water1 evolved in such  quantities      
during volcanic outbursts1 could be     
brought about2 and  moreover1 we can    
scarcely regard the production of       
fissures in the  earth's crust as being 
at the same time both the cause and the 
effect  of this influx of water to the  
deep-seated rock-masses at a high       
temperature4    ,sidenote3 ,,absorption 
,,of ,,gases ,,by ,,liquids ,,and       
,,solids4    ,during recent years the   
attention of both geologists and        
physicists  has been directed to a      
remarkable property exhibited by many   
liquids  and solids1 as supplying a     
possible explanation of the phenomena of
  volcanic action4 ,the property to     
which we refer is that whereby some     
liquid and solid substances are able to 
absorb many times their volume  of      
certain gases--which gases under        
different conditions may be given  off  

again from the liquids or solids4 ,this 
power of absorption is a  very          
remarkable one2 it is not attended with 
chemical combination1 but  the amount of
 condensation which gases must undergo  
within the solid or  liquid substances  
is sometimes enormous4 ,water may be    
made to absorb  more than #a1jjj times  
its volume of ammonia1 and more than    
#ejj times  its volume of hydrochloric  
acid4 ,alcohol may absorb more than #cjj
  times its volume of sulphurous acid4  
,charcoal may absorb #ajj times its     
volume of ammonia1 #he times its volume 
of hydrochloric acid1 #fe times  its    
volume of sulphuretted hydrogen1 #ee    
times its volume of sulphurous  acid1   
and #ce times its volume of carbonic    
acid4 ,platinum-black absorbs  many     
times its volume of oxygen and other    
gases4    ,this power of absorption of  
gases varies in different solids and    
liquids according to the conditions to  
which they are subjected4 ,dr4  ,henry  
showed it to be a general law in liquids

 that1 as the pressure is  augmented1   
the weight of the gas absorbed is       
proportionately increased4    ,sometimes
 this absorption of gases takes place   
only at high  temperatures4 ,thus silver
 in a state of fusion is able to absorb 
#bb  times its volume of oxygen gas4    
,when the metal is allowed to cool this 
gas is given off1 and if the cooling    
takes place suddenly a crust is  formed 
on the surface1 and the phenomenon known
 as the 'spitting of  silver' is        
exhibited4 ,sometimes during this       
operation miniature cones  and          
lava-streams are formed on the surface  
of the cooling mass1 which  present a   
striking resemblance to those formed on 
a grand scale upon  the surface of the  
globe4 ,similar phenomena are exhibited 
by several  other metals and by the     
oxide of lead4    ,the researches of    
,troost and others have shown that      
molten iron and  steel possess the      
property of absorbing considerable      
quantities of  oxygen1 hydrogen1        

carbonic acid1 and carbonic oxide1 and  
that these  gases are given off in the  
operation known as 'seething1' when     
either  the pressure or the temperature 
is diminished4    ,hochstetter has shown
 that in the process of extracting      
sulphur from  the residues obtained     
during the manufacture of soda1 some    
very  interesting phenomena are         
manifested4 ,the molten sulphur is      
exposed  to a temperature of #bfb       
,fahrenheit1 and a pressure of two or   
three  atmospheres1 in the presence of  
steam2 under these circumstances it  is 
found that the sulphur absorbs a        
considerable quantity of water1  which  
is given off again with great violence  
from the mass as it  undergoes          
solidification4 ,the hardened crust     
which forms on the surface  of the      
molten sulphur is agitated and fissured1
 miniature cones and  lava-streams being
 formed upon it1 which have a striking  
resemblance to  the grander phenomena of
 the same kind exhibited upon the crust 

of the  globe4    ,the observations     
which we have described prove           
conclusively that many  liquids and     
solids in a molten condition have the   
power of absorbing  many times their    
volume of certain gases1 and that this  
action is aided  by heat and pressure4  
,that the molten materials which issue  
from volcanic vents have  absorbed      
enormous quantities of steam and other  
gases1 we have the  most undisputable   
evidence4 ,the volume of such gases     
given off  during volcanic outbursts1   
and while the lava-streams are flowing  
and consolidating1 is enormous1 and can 
only be accounted for by  supposing that
 the masses of fluid rock have absorbed 
many times their  volume of the gases4  
,but we have another not less convincing
 proof  of the same fact in the         
circumstance that volcanic materials    
which  have consolidated under great    
pressure--such as granites1 gabbros1    
porphyries1 c4--exhibit in their        
crystals innumerable cavities           

containing similar gases in a liquefied 
state4    ,it is to the violent escape  
of these gases from the molten          
rock-masses1  as the pressure upon them 
is relieved1 that nearly all the active 
phenomena of volcanoes must be referred2
 and it was the recognition of  this bet
 by ,spallanzani1 while he was watching 
the phenomena displayed  in the crater  
of ,stromboli1 which laid the           
foundations of the science  of          
,vulcanology4    ,sidenote3 ,,source    
,,of ,,the ,,absorbed ,,gases4    ,but  
here another question presents itself to
 the investigator of the  phenomena of  
volcanoes3 it is this4 ,at what period  
did the molten  rock-masses issuing from
 vents absorb those gaseous materials   
which  are given off so violently from  
their midst during eruptions8 ,two      
different answers to this question have 
been suggested4 ,it may be that  the    
original materials of which our globe   
was composed consisted of  metallic     
substances in a state of fusion which   

had absorbed many gases1  and that1 in  
the fluid masses below the solid crust1 
vast quantities of  vapour and gas are  
stored up1 which are being gradually    
added to the  atmosphere during volcanic
 outbursts4 ,the fact that meteorites1  
which1  as we have seen1 in all         
probability closely resemble the        
materials  forming the earth's interior1
 sometimes yield many times their volume
  of hydrogen and other gases1 may be   
thought to lend some support to  this   
idea4 ,if it be the correct one1 we must
 regard our globe as  gradually parting 
with its pent-up stores of energy1 in   
those absorbed  gases and vapours held  
in bondage by the solid and fluid       
materials of  its interior4    ,but     
there is another hypothesis which is1 to
 say the least1 equally  probable4      
,water containing various gases in      
solution is continually  finding its way
 downwards by infiltration into the     
earth's crust4  ,much of this water1    
after passing through pervious beds1    

reaches  some impervious stratum and is 
returned to the surface in the form  of 
springs4 ,but that some of this         
percolating water penetrates to         
enormous depths is shown by the fact    
that the deepest mines and borings      
encounter vast underground supplies of  
water4 ,when we remember that  nearly   
three-fourths of the earth's surface is 
covered by the waters  of the ocean1 and
 that the average depth of these oceanic
 waters is  more than #aj1jjj feet1 we  
may easily understand how great a       
portion of  the earth's crust must be   
penetrated by infiltrating waters which 
can  find no outlet in springs4 ,the    
penetration of the waters of the ocean  
into the earth's crust will be aided1   
too1 by the enormous pressure  amounting
 to not less than several tons to the   
square-inch upon the  greater part of   
the ocean-floor4 ,it might be thought   
that this downward  penetration of water
 would be counteracted by the upward    
current of  steam that would be produced

 as these subterranean waters reach the 
hotter portions of the earth's crust4   
,but the experiments of ,daubre  have   
conclusively shown that the penetration 
of water through rocks  takes place in  
opposition to the powerful pressure of  
steam in the  contrary direction4       
,hence1 we may assume that certain      
quantities of  water1 containing various
 gases and solids in solution1 are      
continually  finding their way by       
capillary infiltration from the surface 
to  the deeply seated portions of the   
earth's crust1 there to undergo         
absorption by the incandescent          
rock-masses and to produce oxidation of 
some of their materials4    ,sidenote3  
,,position ,,of ,,the ,,isogeotherms4   
,the deep-sea soundings of the          
',challenger' have shown that the floor 
of  the ocean is constantly maintained  
at a temperature but little above  that 
of the freezing point of water4 ,this   
low temperature is probably  produced by
 the absorption of heat from the earth's

 crust by the waters  of the ocean1     
which distribute it by means of         
convection currents on  the grandest    
scale4 ,hence1 the isogeotherms1 or     
lines indicating the  depths at which   
the same mean temperature is found      
within the earth's  crust1 are probably 
depressed beneath the great             
ocean-floors1 and rise  towards the     
land-masses4 ,it is to this             
circumstance1 combined with  that of the
 enormous pressure of water on the      
ocean-beds1 that we must  probably      
ascribe the general absence of volcanoes
 in the deep seas and  their            
distribution near coast-lines4    ,we   
have thus briefly reviewed the chief    
hypotheses which have been  suggested in
 order to account for the two great     
factors in all volcanic                 
phenomena--namely1 the presence of      
highly heated rock-masses within  the   
earth's crust1 and the existence of     
various vapours and gases in a  state of
 most intimate mechanical1 but not      

chemical1 union with these  incandescent
 materials4 ,it must be admitted that we
 do not at present  appear to have the  
means for framing a complete and        
consistent theory  of volcanic action1  
but we may hopefully look forward to the
 time when  further observation and     
experiment shall have removed many of   
the  existing difficulties which beset  
the question1 and when by the light  of 
such future researches untenable        
hypotheses shall be eliminated and  the 
just ones improved and established4     
,but if we are constrained to admit that
 a study of the observed  phenomena and 
established laws of volcanic action have
 not as yet  enabled us to frame any    
complete and satisfactory theory on the 
subject1 we cannot lose sight of the    
fact that all modern speculation  upon  
this question appears to be tending in  
one definite direction4 ,it  is every   
day becoming more and more clear that   
our earth is bound by  ties of the      
closest resemblance to the other members

 of that family of  worlds to which it  
belongs1 and that the materials entering
 into their  constitution1 and the      
forces operating in all are the same4   
,we have had occasion in a previous     
chapter to point out that there  are the
 strongest grounds for believing the    
interior of our globe to  consist of    
similar materials to those found in the 
small planetary  bodies known as        
meteorites4 ,that the comets are merely 
aggregations  of such meteorites1 and   
that the planets differ from them only  
in  their greater dimensions1 may be    
regarded as among the demonstrated      
conclusions of the astronomer4 ,the     
materials found most abundantly in      
meteorites and in the interior of our   
globe are precisely the same as  those  
which are proved to exist in an         
incandescent state in our sun4  ,hence  
we are led to conclude that the whole of
 the bodies of the solar  system are    
composed of the same chemical elements4 
,sidenote3 ,,eruptive ,,action ,,in     

,,the ,,sun4    ,that the forces        
operating in each of these distant      
bodies present  striking points of      
analogy is equally clear4 ,the sun is of
 far greater  dimensions than our earth1
 and is still in great part1 if not     
entirely1  in a gaseous condition4 ,the 
great movements in the outer envelopes  
of  the sun exhibited in the 'sun-spots'
 and 'solar prominences1' recall  to the
 mind the phenomena of volcanic activity
 upon our globe4 ,but  the vast energy  
still existing in the intensely heated  
mass of the  sun1 and the wonderful     
mobility of its gaseous materials1 give 
rise to  appearances beside which all   
terrestrial outbursts seem to sink into 
utter insignificance4 ,vast cavities of 
such dimensions that many globes  of the
 size of our earth might be swallowed up
 in them are formed  in the solar       
envelopes in the course of a few days or
 hours4 ,within  these cavities or      
sun-spots incandescent vapours are      
observed1 rushing  upwards and downwards

 with almost inconceivable velocity4    
,the drawings made by ,secchi1 and      
reproduced in figs4 #hi and #ij1 will   
give some idea of the appearances       
presented by these great holes in the   
solar envelopes4    ,illustration3 ,fig4
 #hi4--;,a group of ,sun-spots4 7,after 
,secchi47    ,in fig4 #hi a group of    
sun-spots is represented and1 in their  
circular  outlines and tendency to a    
linear arrangement1 they can scarcely   
fail  to remind anyone familiar with    
volcanic phenomena of terrestrial       
craters1 though their dimensions are so 
much greater4    ,in fig4 #ij the       
sun-spot represented shows the presence 
of large  floating masses of            
incandescent materials rushing upwards  
and downwards  within the yawning gulf4 
,sidenote3 ,,phenomena ,,of             
,,sun-,,spots4    ,illustration3 ,fig4  
#ij4--;,a ,sun-spot1 showing the great  
masses of  incandescent vapour rising or
 falling within it4 7,after ,secchi47   
,illustration3 ,fig4 #ia4--,the edge of 

a ,sun-spot1 showing a portion of  the  
prominent masses of incandescent gas    
7,a71 which detached itself at  ,e and  
floated into the midst of the cavity4   
,from fig4 #ia1 taken from a drawing by 
,mr4 ,norman ,lockyer1 we may           
understand the movements of these great 
protuberances of incandescent  gas which
 are seen on the sides of the sun-spots4
    ,the so-called solar prominences    
present even more striking resemblances 
to the volcanic outbursts of our globe4 
,two drawings made by ,mr4 ,norman      
,lockyer will serve to give some idea   
of the vast dimensions of these solar   
prominences1 and of the rapid  changes  
which take place in their form4         
,illustration3 ,fig4 #ib4--;,drawing of 
a ,solar prominence1 made by ,mr4       
,norman ,lockyer on ,march #ad1 #ahfi1  
at #aa ,h4 #e ,m4 ,a4,m4    ,the masses 
of incandescent gas were estimated as   
being no less than  #bg1jjj feet in     
height1 yet in ten minutes they had     
totally changed  their form and         

appearance1 as shown in fig4 #ic4       
,even still more striking are the       
changes recorded by ,professor ,young1  
of ,new-,haven1 in a solar prominence1  
which he observed on ,september #g1     
#ahga4    ,illustration3 ,fig4          
#ic4--,the same object1 as seen at #aa  
,h4 #ae ,m4 on the  same day4           
,sidenote3 ,,solar ,,prominences4       
,that astronomer described a mass of    
incandescent gas rising from  the       
surface of the sun to the height of     
#ed1jjj miles4 ,in less than            
twenty-five minutes he saw the whole    
mass torn to shreds and blown  upwards1 
some of the fragments being in ten      
minutes hurled to the  height of        
#bjj1jjj miles above the sun's surface4 
,the masses of  incandescent gas thus   
hurled upwards were of enormous         
dimensions1 the  smallest being         
estimated as having a greater area than 
the whole of the  ,british ,islands1 and
 the force with which they were urged   
upwards was  so great that they acquired

 a velocity of #aff miles per second4   
,the  accompanying woodcut shows the    
successive appearances presented by this
  grand eruptive outburst on the surface
 of the sun4    ,illustration3 ,fig4    
#id4--;,drawings of a ,solar prominence 
at four  different periods on ,sept4 #g1
 #ahga4 7,after ,young47    ,sidenote3  
,,extinct ,,volcanoes ,,of ,,the ,,moon4
    ,the moon1 which is of far smaller  
size than our earth1 exhibits on  its   
surface sufficiently striking evidences 
of the action of volcanic  forces4      
,indeed the dimensions of the craters   
and fissures which cover  the whole     
visible lunar surface are such that we  
cannot but infer  volcanic activity to  
have been far more violent on the moon  
than it  is at the present day upon the 
earth4 ,this greater violence of the    
volcanic forces on the moon is perhaps  
accounted for by the fact that  the     
force of gravity on the surface of the  
moon is only one-sixth of  that at the  
surface of the earth2 and thus the      

eruptive energy will  have a much less  
smaller resistance to overcome in       
bursting asunder the  solid crust and   
accumulated heaps of ejected materials  
on its surface4  ,but the volcanic      
action on the moon appears now to have  
wholly ceased1  and the absence of both 
water and atmosphere in our satellite   
suggests  that this extinction of       
volcanic energy may have been caused by 
the  complete absorption of its gaseous 
envelope4 ,the appearance presented  by 
a portion of the moon's surface is shown
 in fig4 #ie4    ,the sun and the moon  
appear to exhibit two widely separated  
extremes  in the condition assumed      
during the cooling down from a state  of
 incandescence of great globes of       
vaporised materials4 ,the  several      
planets1 our own among the number1      
probably exhibit various  intermediate  
stages of consolidation4                
,illustration3 ,fig4 #ie4--;,a group of 
,lunar craters 7,maurolycus1  ,barocius1
 etc471 the largest being more than #fj 

miles in diameter4    ,sidenote3        
,,eruptive ,,action ,,in ,,the ,,sun1   
,,earth ,,and ,,moon4    ,our earth is1 
as we have seen1 closely allied to the  
other bodies of  the solar system in its
 movements1 its relations1 and its      
composition2  and a true theory of      
terrestrial vulcanicity1 when it is     
discovered1  may be expected not only to
 afford an explanation of the phenomena 
displayed on our own globe1 but to      
account for those displays of  internal 
energy which have been manifested in    
other members of the same  great family 
of worlds4          ,,index4      ,the  
subjects illustrated in the engravings  
are indicated by italics1  the names of 
authors are in ,capitals4      ,,abich1 
cited1 #abb    -- researches of1 #d     
,absorption of gases by liquids and     
solids1 #ced1 #cee    ,acid lavas1 #dh  
olian ,islands4 ,see ,lipari ,islands   
olus1 origin of myth1 #ce    ,africa1   
volcanoes of1 #bbg    -- ,south1        
diamonds of1 #adg    ,agates1 formation 

of1 #aej    ,allport1 ,mr41 cited1 #bei 
,alps1 formation of1 #bib    ,altered   
lavas1 names given to1 #bfa    ,america1
 volcanoes of1 #bbg    ,amygdaloids1    
formation of1 #adj1 #ada    ,andesites1 
#ej1 #ei    ,andesite-volcanoes1 #abf   
,andrews1 ,professor1 cited1 #cba       
,anne ,boleyn and ,etna1 #c             
,armstrong1 ,sir ,w41 hydro-electric    
machine1 #bi    ,arthur's ,seat1 #bge   
,artificial stone1 #ee    ,asia1        
volcanoes of1 #bbg    ,asiderites1 #caf 
,asmanite1 #cad    ,astroni1 crater-ring
 of1 #agj    ,atlantic1 volcanoes in1   
#bbc    ,auvergne1 breached cones of1   
#abc1 fig4 #dj    -- denuded cones in1  
#abd1 fig4 #db    -- incrusting springs 
of1 #ahd    -- puys of1 #aeb1 #bab    --
 volcanic cones in1 #gi                 
,,ball-,,and-,,socket structure in      
basaltic columns1 #ajg    ,barrancos1   
formation of1 #bji    ,basalt1          
controversy concerning origin of1 #bdi  
,basalts1 #di1 #ej1 #ei    ,basaltic    
columns of ,bohemia1 #ajg    -- -- of   

,central ,germany1 #ajg    -- -- of     
,monte ,albano1 #ajg    -- -- from the  
,giant's ,causeway1 #ajg1 fig4 #bi      
,basic lavas1 #dh    ,bath1 hot spring  
of1 #bai    ,ben ,nevis1 #bgd           
,bohemia1 volcanoes of1 #abf    -- lavas
 of1 #ajc    ,boiling4 ,see ,ebullition 
,bonney1 ,professor1 cited1 #fi1 #aji1  
#bei    ,boracic acid at volcanic vents1
 #baf    ,bourbon1 volcano of1 #agf1    
figs4 #gd1 #ge    ,bracciano1           
crater-lake of1 #agh1 fig4 #gg          
,breached cones1 #abc1 fig4 #dj         
,babbles of steam1 escape from lava1 #ba
    ,bubbles1 spontaneous movement of1  
in liquid cavities1 #fb1 fig4 #h    --  
-- cause of1 #fe    ,buch1 ,von1        
researches of1 #d    ,buda-,pesth1 deep 
well of1 #cce1 #cda    ,bdos ,hegy1     
,transylvania1 #bae    ,bunsen1 cited1  
#bja    ,burning1 does not take place at
 volcanoes1 #b      ,,cader ,,idris1    
#bgd    ',calderas1' formation of1 #ahj 
,caldera of ,palma1 #bji                
,cambro-,silurian volcanoes of ,british 

,islands1 #bgd    ,campi-,phlegri1 map  
of1 fig4 #aa    -- -- volcanoes of1 #gi 
-- -- tuff-cones of1 #aah    -- --      
fissures in1 #aig    ,carbonic acid in  
cavities of crystals1 #fc               
,carboniferous volcanoes of ,british    
,islands1 #bge    ,carlsbad1 ,strudel   
of1 #bah    -- ,strudelstein of1 #ahd   
,caspian ,sea1 mud-volcanoes of1 #ahb   
,catacecaumene1 volcano cones in1 #gi   
,cause of proximity of volcanoes to sea1
 #bci    ,central ,asia1 volcanoes of1  
#bcf    -- ,america1 mud-volcanoes1 #ahb
    -- ,pacific1 volcanoes of1 #bcf     
',challenger1' ,h4,m4,s41 voyage of1 #gc
    -- -- soundings of1 #cei    ,chance1
 ,messrs41 of ,birmingham1 #ee          
,charnwood ,forest1 ancient volcanic    
rocks of1 #bei    ,chemical deposits at 
,vulcano1 #dd    -- -- on surfaces of   
lavas1 #aaj    -- elements present in   
lavas1 #df    -- theory of volcanoes1   
#cdd1 #cdf    ,chiaja di ,luna1 #ajh    
,chimborazo1 size of1 #dd    -- #aea    
,chodi-,berg1 ,hungary1 #afa            

,citlaltepetl1 view of1 #afi1 fig4 #fi  
,coast-lines1 proximity of volcanoes to1
 #bbh    ,cole1 ,mr4 ,grenville1 #aaj   
,colours of lavas1 #di    ,columns in   
lava1 #aje    -- -- dimensions of1 #aje 
-- radiating in intrusive masses1 #acf  
,columnar structure in lavas1 #ajd    --
 -- origin of1 #aje    ,columnar        
lava-stream on the ,ardche1 #ajg1 fig4  
#bh    ,combustion1 does not take place 
at volcanoes1 #b    ,composite cones1   
#abh1 #afa    ,comstock mines1          
temperature of1 #cdb    ,concentric     
jointing in lava1 #ajh1 fig4 #cj        
,cones composed of viscid lava1 #abi1   
fig4 #dc    -- miniature on             
lava-streams1 #ajj1 #aja1 figs4 #be1 #bf
    -- natural sections of1 #abi    --  
shifting of axis in1 #afg    ,coolin    
,hills1 ,skye1 #add    ,cotopaxi1       
volcanic dust of1 #fi    -- view of1    
#afh1 fig4 #fh    ,craters1 formation   
of1 #hb    -- origin of1 #afg    --     
position of1 #afg    -- fissuring of    
sides1 #ahj    ,crater of ,stromboli1   

aperture at bottom of1 #ae              
,crater-lakes1 formation of1 #aga    -- 
of ,agnano1 #aga    -- of ,albano1 #aga 
-- of ,avernus1 #aga    -- of ,bagno1   
#aga1 fig4 #ga    -- of ,bolsena1 #aga  
-- of ,bracciano1 #aga    -- of         
,frascati1 #agc1 #age    -- of          
,gustavila1 #aga1 fig4 #gb    -- of     
,laach1 #aga    -- of ,nemi1 #aga       
,crater-rings1 formation of1 #agj       
,crater-ring of ,somma1 #agg1 fig4 #gf  
,crater-ring of ,pianura1 #agd    -- -- 
of ,piano di ,quarto1 #agd    -- -- of  
,vallariccia1 #agd    ,creuzot1 shafts  
at1 #cdj    ',critical point' of        
liquids1 #fc    ,crust of globe1        
definition of1 #cjh    ,crystals in     
lavas1 #ea    -- -- formed of           
crystallites1 #ed-eg    -- -- formed in 
subterranean reservoirs1 #fj    -- --   
interruption in growth of1 #fj    --    
pressure under which formed1 #fe    --  
deposited on surface of lava1 #aaj    --
 porphyritic1 origin of1 #bef           
,crystalline minerals formed beneath    

volcanoes1 #adf1 #adg    -- -- ejected  
from volcanoes1 #adg    ,crystallised   
minerals of volcanoes1 #df              
,crystallites1 aggregates of1 #ed1      
,frontispiece    ,crystallites in lavas1
 #ec1 ,frontispiece                     
,crypto-crystalline base1 #eg           
',cupolas1' #ace    ,corral of ,madeira1
 #bji      ,,dacites1 #aih    ,dana1    
,professor1 ,j4 ,d41 cited1 #ajj1 #aei1 
#bia1 #cja1 #cbg1 #cch1 #cci    ,darwin1
 ,mr41 cited1 #bde1 #bdf1 #bga1 #bhi    
,daubeny1 cited1 #ahb    ,daubre1 ,m41  
cited1 #adg1 #cae1 #cbj1 #ceh           
,daubrelite1 #cad    ,davy1 ,sir        
,humphry1 chemical theory of volcanoes1 
#cdd1 #cde    ,deccan of ,india1 #ajc   
,density of the earth1 #cjf    ,denuded 
cones and craters1 #aeh1 fig4 #ei       
,denudation1 effects of1 on volcanoes1  
#aad    ,deposits about volcanic        
fissures1 #db    ,detonations at        
,vesuvius1 #bf    ,devonian volcanoes of
 ,british ,islands1 #bgd    ,diorite1   
#ei    ,dolomieu1 cited1 #d1 #ci        

,durocher1 cited1 #bja    ,dykes1       
formation of1 #aaf1 #aag1 #bji1 #baj    
-- structure of rock in1 #baa    --     
pseudo-1 #aai    ,dynamical theory of   
volcanoes1 #cdg1 #cdh      ,,earth',s   
interior1 nature of1 #cji    -- --      
physical condition of1 #cbe    -- --    
hypothesis concerning1 #cbh-ccj    --   
relation to other planets1 #caj1 #caa   
,earthquakes1 depth of origin of1 #cdc1 
#cdd    -- connection with volcanoes1   
#cdc    -- accompanying ,vesuvian       
eruption of #ahgb1 #bg    ,ebullition1  
compared to volcanic eruptions1 #ai1 #bj
    ,eifel1 volcanic cones of1 #de      
,ejected blocks1 #de    -- materials1   
height to which thrown1 #gb    -- --    
stratification of1 #aag-aai             
,elements1 pyroxenic and trachytic1     
theory of1 #bja    ,elevation-craters1  
theory of1 #ace1 #bjj    ,erroneous     
opinions1 sources of1 in regard to      
volcanoes1 #b    ,eruptions1 feeble and 
violent compared1 #ca    -- prediction  
of1 not possible1 #cb    -- intervals   

between1 #cc    -- of varying intensity1
 #cc    -- and barometric pressure1 #cf 
-- effects of repetition of from same   
fissure1 #hj    ,eruptive action in sun 
and moon1 #cfj-cfi    ,etna1 ideas of   
ancients concerning1 #c    -- and ,anne 
,boleyn1 #c    -- observatory on1 #cg   
-- size of1 #dd    --1 #aea    --       
eruptions at summit and on flanks1 #bjg 
,etna1 dyke and lava-stream in1 #acc1   
fig4 #ed    ,etna1 views of1 #afb1 #afc1
 figs4 #fb1 #fc    ,euganean ,hills1    
#aci    -- -- volcanoes of1 #bja        
,europe1 volcanoes of1 #bbg             
,extra-terrestrial rocks1 #caf          
,extra-terrestrial rocks1 relation to   
ultra-basic rocks1 #cbb1 fig4 #hh       
,,felstones1 #bfc    ,ferric-chloride1  
mistaken for sulphur1 #da    ,fissure on
 flanks of ,etna1 #aid1 fig4 #hd        
,fissure-eruptions1 #ahh    ,fissures1  
volcanic cones on1 #aid    -- systems   
of1 #aih    ,fingal's ,cave1 #ajf       
,flames1 phenomena mistaken for1 #b     
-- at volcanoes1 feebly luminous1 #ag   

-- false appearance of1 in volcanoes1   
#ag    ,flames at volcanic vents1 #da   
,flashing lighthouse1 compared to       
,stromboli1 #aj    ,floods1 accompanying
 volcanic outbursts1 #cj    ,forbes1    
,mr4 ,david1 cited1 #ccg1 #cci          
,fossils1 from beneath ,vesuvius1 #de   
-- supposed in basalt1 #bej    ,fouqu1  
,m41 cited1 #aaj1 #bac    ,fumaroles1   
gases emitted from1 #bac    ,fusiyama1  
form of1 #ij1 #aff    ,fusiyama1 #agh1  
fig4 #gg      ,,gabbro1 #ei             
,gardiner's river1 travertine terraces  
of1 #ahe    ,gases emitted from         
volcanoes1 #dj    -- -- volcanic vents1 
#bab-baf    ,geanticlinals1 formation   
of1 #big    ,gems1 formation of1 #adg   
-- mode of occurrence1 #adh             
,geological continuity1 doctrine of1    
#bdg    ,geosynclinals1 formation of1   
#bid    ,geysers1 formation of1 #bag    
-- intermittent action of1 #bah    -- of
 ,colorado1 #ahd1 #bag    -- of         
,iceland1 #ahd1 #bag    ,giant's        
,causeway1 #ajh    ,gilbert1 ,mr4 ,g4   

,k41 cited1 #bjh    ,girgenti1          
mud-volcanoes of1 #ahb    ,glass1 formed
 by fusion of lavas1 #eb    ,glasses1   
composed of certain silicates1 #eh      
,glassy base1 #eg    ,goethe1 cited1    
#aab    ,graham ,isle1 #agh1 #agi1 fig4 
#gh    ,graham1 cited1 #cde    ,grand   
,sarcoui1 ,auvergne1 #afa    ,granite1  
#ei    ,granite of ,secondary and       
,tertiary ages1 #bed    ,granitic rocks1
 position beneath volcanoes1 #ade       
,great earth movements1 nature of1 #bhf 
,great volcanic bands of the globe1     
#bcb-bcd    ,grenelle1 boring of1 #cda  
,greystones1 #di    ,groundmass of      
lavas1 #eb    ,grotto del ,cane1 #bae   
,guevo ,upas1 ,java1 #bae    ,guiscardi1
 ,professor1 referred to1 #de           
,gustavila1 crater-lake of1 #agb1 fig4  
#gb      ,,hamilton1 ,sir ,w41          
researches of1 #d1 #ge1 #hd    -- --    
observations on ,vesuvius1 #hj          
,hannay1 ,mr41 referred to1 #adg        
,hartley1 ,mr4 ,noel1 referred to1 #fe  
,hawaii1 volcanoes of1 #ajj1 #abe    -- 

-- lava-masses of1 #aei    -- --        
volcanic eruptions at different levels1 
#cbg    ,hebrides1 volcanoes of1 #bga   
,henry1 ,dr41 cited1 #cee    ,henry     
,mountains1 ,southern ,utah1 #bjh       
,hephstus1 forge of1 #c    ,hochstetter1
 cited1 #ace1 #cef    ,holosiderites1   
#cae    ,hopkins1 ,mr41 cited1 #cdi     
,hot springs1 numbers of1 #bai          
,humboldt1 researches of1 #d            
,hungary1 lavas of1 #if1 #ajc    --     
volcanoes of1 #abf1 #bja    -- deep     
wells of1 #cda    ,hverfjall1 ,iceland1 
#agh1 fig4 #gg    ,hydro-electric       
machine of ,sir ,w4 ,armstrong1 #bi     
,hypothesis1 value of1 #cca-ccc         
,,ice under lava of ,vesuvius in #ahgb1 
and of ,etna1 #aaj    ,iceland1 volcanic
 dust of1 carried to ,norway1 #gb       
,indian ,ocean1 volcanoes in1 #bbi      
,insel ,ferdinandez1 #agh1 #agi1 fig4   
#gh    ,intermediate lavas1 #dh         
,intervals between ,eruptions1 #cc      
,ireland1 north-east of1 #ajc    ,iron  
in ,ovifak-basalts1 #cai1 fig4 #hg      

,iron1 seething of1 #cef    -- of       
,ovifak1 terrestrial origin of1 #cbj    
,ischia1 eruption in #acja1 #afd    --  
crater-lake of ,bagno in1 #agb1 fig4 #ga
    -- plan of1 #afc1 fig4 #fd    --    
parasitic cones in1 #afd1 fig4 #fe      
,island of ,bourbon1 #ic    ,isle       
,julie1 #agh1 #agi1 fig4 #gh            
,isogeotherms1 #cei      ,,janssen1     
referred to1 #db    ,joint-structures in
 lava1 #ajd-aaj      ,,kammerb,,hl1     
#aab-aad1 fig4 #cc    -- section of1    
#aad1 fig4 #cd    -- section in side of1
 #aah1 fig4 #cf    ,kant1 nebular       
hypothesis of1 #ceb    ,kilauea1 volcano
 of1 #ga1 #ach    -- crater of1 #aha    
,king1 ,mr4 ,clarence1 cited1 #cja      
,,laacher ,,see1 minerals ejected at1   
#adi    ,lac ,paven1 ,auvergne1 #aga1   
fig4 #gj    ',laccolites1' formation of1
 #bjh    ,lago di ,bolsena1 #agc1 #age  
,lago di ,bracciano1 dimensions of1     
#agb1 #agc    ,lake ,avernus1 #bae      
,lapilli1 #gj    ,laplace1 nebular      
hypothesis of1 #cbe1 #ceb    ,lavas1    

action of acid gases on1 #da    --      
resemblance to slags1 #df    -- chemical
 elements in1 #df    -- oxygen in1 #dg  
-- silicon in1 #dg    -- proportion of  
silica and other oxides in1 #dg    --   
silicates in1 #dg    -- acid1           
intermediate1 basic1 #dh    -- specific 
gravities of1 #di    -- colours of1 #di 
-- microscopic study of1 #ej    --      
fusibility of1 #ea    -- minerals in1   
#ea    -- artificially fused1 #ea    -- 
crystals in1 #ea1 #ic    -- ground mass 
of1 #eb    -- crystalline forms of1 #ei 
-- of ,bohemia1 #ajc    -- of ,hungary1 
#if1 #ajc    -- of ,kilauea1 #ie    --  
of ,lipari1 #if    -- of ,niedermendig1 
#ajc    -- of ,vesuvius1 #ajd    -- of  
,volvic1 #ie    -- of ,volcano1 #ie     
-- presence of water ,in1 #ajb    --    
chemical deposits on1 #aaj    --        
different fluidity of1 #bjd    -- augite
 and hornblende in1 #bfg    ,lava1      
cascade of1 #ic1 fig4 #ah               
,lava-cones1 composed of liquid lava1   
#abe    -- -- of viscid lava1 #abf1 #abg

    -- characters of1 of liquid lava1   
#aei    -- -- of viscid lava1 #afj      
,lava-cones1 outlines of1 #afj1 fig4 #fj
    ,lava1 in deep-seated reservoirs1   
#ach    -- consolidation of1 at great   
depths1 #aci    ,lava-fountains1 #id    
,lava-sheets1 intrusive1 #acf1 #acg1    
fig4 #ef    ',lava' ornaments of        
,naples1 #de    ',lava1' slow-cooling   
of1 #aaj    -- a bad conductor of heat1 
#aaj    -- ice under1 #aaj              
,lava-streams1 nature of movements1 #ib 
-- difference in liquidity of1 #ib    --
 miniature cones on1 #ajj1 #aja    --   
vast dimensions of1 #ajb    -- structure
 of1 #ajc    -- position of columns in1 
#ajf    -- sinking of surface of1 #aaa  
',lave di fango1' #cj    ',lave di      
fuoco1' #cj    ,lawrencite1 #cad        
,laws of volcanic action1 #ch    ,le    
,conte1 cited1 #cdg    ,leucite1 absence
 from ancient lavas1 #bfh    ,lightning1
 accompanying volcanic outbursts1 #bh   
,linear arrangement of volcanic vents1  
#aia    -- -- of volcanoes1 #bca        

,lipari ,islands1 #c1 #ci    -- --      
fissures in1 #aig    -- -- pumice-cones 
in1 #aed    -- -- order of appearance of
 lavas in1 #bjj    -- -- breached       
pumice-cones in1 #abd1 fig4 #da    -- --
 map of1 #aib1 fig4 #ha    -- -- lavas  
of1 #if1 figs4 #bj1 #ba    ,liquids in  
cavities of crystals1 #fc    ,liquid    
cavities in lavas1 #fj1 fig4 #g    -- --
 spontaneous movement of bubbles in1    
#fb1 fig4 #h    -- -- spontaneous       
movement of bubbles in1 cause of1 #fe   
,lockyer1 ,mr4 ,norman1 cited1 #cbb1    
#cfc1 #cfd    ,lunar craters1 #cfh1 fig4
 #ie    ,lyell1 ,sir ,charles1 cited1   
#ace1 #afg1 #aig      ,,macculloch1     
cited1 #bjg1 #bjh    ,madeira1          
cliff-section in1 #abh1 fig4 #dg        
,magmas1 theory of1 #bja    --          
objections to1 #bjb1 #bjc    ,mallet1   
,mr41 cited1 #bfi1 #cdc1 #cdf           
,mamelons of ,bourbon1 #abf1 #abg1 figs4
 #de1 #df    ,maskelyne1 ,professor1    
cited1 #cad    ,massa di ,somma1        
destruction of1 #bf    ,mauna ,loa1 #ach

    ,metamorphism around volcanic vents1
 #ade    ,meteorites1 nature of1 #cab   
-- composition of1 #cac    -- minerals  
of1 #cad    -- classification of1 #cae  
,melaphyres1 #bfb    ,miascite1 #ei     
,michel ,lvy1 ,m41 #aaj                 
,micro-crystalline base1 #eh            
,microliths4 ,see ,crystallites         
,microscopic study of lavas1 #ej        
,minerals in lavas1 #ea    -- of        
,vesuvius1 #df    ,mineral-veins1       
formation of1 #adi    -- connection with
 volcanoes1 #bbj    -- nature of        
materials in1 #cba    ,misenum1 ,cape   
of1 section of tuff-cone of1 #aba1 fig4 
#ch    ,modena1 mud-volcanoes of1 #ahb  
,mont ,dore1 section at1 #acj1 fig4 #dh 
,monte ,cerboli1 ,tuscany1 #baf         
,monte ,massi1 ,tuscany1 well at1 #cda  
,monte ,nuovo1 history of formation of1 
#gf    -- -- description of1 #gg1 #gh1  
fig4 #aj    -- -- #aeb    -- -- crater  
of1 #afh    -- -- production of fissure 
at1 #aij    ,monte ,rotondo1 ,tuscany1  
#baf    ,moon1 effect of internal forces

 on1 #cje    ,mountains1 all volcanoes  
not1 #b    ,mountain-chains1 formation  
of1 #bia    -- -- all of recent date1   
#bib    ,mud-streams at volcanoes1 #cj  
,mud-volcanoes1 formation of1 #aha1 #ahb
    ,mull1 dissected volcano of1 #adb-d1
 figs4 #eg1 #eh    ,muscovite1 absence  
of1 from modern lavas1 #bfh             
,,nebular hypothesis of ,laplace1 #cbe1 
#ceb    -- -- of ,kant1 #ceb    ,new    
,zealand1 geysers of1 #bag    -- --     
volcanoes of1 #ace    -- -- volcanic    
cones in1 #gi    ,niedermendig1 lava of1
 #ajc    ,nordenskild1 ,professor1      
cited1 #cah      ,,observatory on       
,vesuvius1 #bd1 #cg    -- on ,etna1 #cg 
,obsidian1 #ei    ,oceans1 depth of1 in 
volcanic areas1 #bdb    ,oceanic        
islands1 volcanoes in1 #bbh    ,oliver1 
,capt4 ,s4 ,p41 #ib    ,oldhamite1 #cad 
,outlines of ,vesuvius1 #hg1 fig4 #ag   
,ovifak1 iron-masses of1 #cai           
,oxidation of materials of globe1 #cbd  
,oxygen1 proportion in lavas1 #dg       
,,pacific1 volcanoes in1 #bbi           

,palmieri1 ,professor1 cited1 #be1 #cg  
,papandayang1 eruption of1 #afi         
,papin's digester1 nature of action in1 
#bb    ,parasitic cones1 formation of1  
#afa1 #afb1 fig4 #fa    ,pele's ,hair1  
#ga    ,perlitic structure1 #aji        
,phillips1 ,mr4 ,j4 ,a41 cited1 #bbj    
,phonolites1 #ej1 #ei                   
,phonolite-volcanoes1 #abf              
,photograph of ,vesuvius eruption1 #bd1 
fig4 #e    ',pine-tree1 appendage of    
,vesuvius1 #bi    ,pitchstones1         
porphyritic1 #fj    ,plateaux formed of 
lava-sheets1 #bgj    ,pliny1 ,elder1    
death of1 #g    ,plombires1 hot springs 
of1 #adg    ,plutonic rocks1 #fa        
,pompeii1 nature of materials covering1 
#aag    ,ponza ,islands1 #ci    ,ponza1 
sections in1 #aca1 #acb1 figs4 #ea1 #eb 
,porphyrites1 #bfc    ,porphyritic      
pitchstones1 #fj    ,potentially liquid 
rock1 #bej    ,pre-,cambrian volcanoes  
of ,british ,islands1 #bgd    ,presence 
of water in lavas1 #cec    ,pressure    
under which crystals were formed1 #fe   

,predazzo1 ancient volcano of1 #afe1    
fig4 #fg    ,propylites1 #aii           
,pseudo-dykes1 #aai    ,pumice1 how     
formed1 #fh    -- cause of white colour 
of1 #ga    -- floating on ocean1 #gc    
-- on ocean-beds1 #gc    ,pumice-cones1 
#aed    ,puy de ,pariou1 ,auvergne1     
#aic1 #aid1 figs4 #hb1 #hc              
,puzzolana1 #hi      ,,rain1            
accompanying volcanic outbursts1 #cj    
,rate of movement of lava-streams1 #ig  
,rath1 ,professor ,vom1 #gb    ,red clay
 of ocean-beds1 #gd    ,red ,mountains1 
,skye1 #add    ,reservoirs beneath      
volcanoes1 #ade    ,reyer1 ,dr4 ,ed41   
experiments of1 #abe1 #afj              
,reykjanes1 eruption of1 in #aghc1 #ajb 
,rhyolites1 #ej1 #ei    ,richthofen1    
,von1 cited1 #aif1 #aii1 #bjj1 #bje     
,rocca-,monfina1 #agh1 fig4 #gg    --   
--1 #bjd    ,rock-masses1 movements of1 
#bhh    ,rocky ,mountains1 #ajc    -- --
 volcanoes of1 #bja    ,rotomahana1     
sinter-terraces of1 #ahe    ,ropy-lavas1
 #ih1 fig4 #bd      ,,salina1 section   

in1 #acb1 fig4 #ec    ,sandwich         
,islands1 lavas of1 #abe    ,san        
,sebastiano1 destruction of1 #bf    ,san
 ,stephano1 section in1 #aca1 fig4 #ej  
,santorin1 #db    ,sarcoui1 ,grand ,puy 
of1 #abf1 fig4 #dd    ,sciarra del      
fuoco1 #ac    ,scoria1 how formed1 #fh1 
#gj    ,scoria-cones1 altered by acid   
gas1 #aee    -- breached1 #aef    --    
characters of1 #aec    -- preservation  
of1 #aee    -- red colour of1 #aed      
,scoria-cone in ,vesuvius1 #abb1 fig4   
#ci    ,scoria-cone near ,auckland1 ,n4 
,z41 #afef1 fig4 #ff    ,schmidt1       
referred to1 #aec    ,schreibersite1    
#cad    ,scrope1 ,mr4 ,poulett1 cited1  
#e1 #fi1 #ajf1 #ace1 #aih1 #bje1 #bab1  
#bch1 #bhi    ,sea of ,azof1            
mud-volcanoes of1 #ahb    ,secchi1      
,father1 cited1 #cfb    ,shiant ,isles1 
#aje    ,silica1 presence in lavas1 #dg 
,silicates in lavas1 #dg    ,silicon1   
proportion in lavas1 #dg    ,siliceous  
sinter1 deposits of1 #bbj    ,silver1   
spitting of1 #cee    ,silvestri1        

,professor1 cited1 #bcj    ,similarity  
of lavas of different ages1 #bfj        
,sinter-cones1 forms of1 #ahc1 fig4 #gi 
,skye1 dissected volcano of1 #add       
,slags1 compared with lavas1 #df        
,smith1 ,lawrence1 cited1 #cbj          
,smoke1 appearance of1 due to steam1 #b 
,snowdon1 #bgd    ,solar prominences1   
#cfd-cff1 figs4 #ib1 #ic1 #id           
,solfatara of ,naples1 #bad             
,solfatara-stage of volcanoes1 #bae     
,somma1 #acc    -- crater-ring of1 #hc  
,sorby1 ,mr4 ,h4 ,c41 referred to1 #ei1 
#beb    ,spallanzani1 early researches  
of1 #d    -- observations on ,stromboli1
 #h    -- cited1 #ci1 #cfg    ,specific 
gravities of lavas1 #di    -- -- of     
glassy and crystalline rocks1 #ei       
,spectroscope in vulcanology1 #da       
,spectrum-analysis1 results of1 #caa    
,specular-iron1 deposited on            
lava-streams1 #aaj    ,sperenberg1      
boring of1 #cda    ,sphrulites1 #ed1    
,frontispiece    ,sporadosiderites1 #caf
    ,stability of crust of globe1 #cbf  

,staffa1 ,isle of1 #ajf    ,steenstrup1 
cited1 #cai    ,steam-engine compared to
 volcano1 #h    ,steam1 emitted by lava 
of ,vesuvius1 #bg    ,sternberg1        
referred to1 #aac    ,st4 ,kilda1 #aha  
,stokes1 ,professor1 #fe    ,st4 ,paul1 
,island of1 #ahj    ,stromboli1 #db1    
#aeh    -- apertures at bottom of       
crater1 #ae    -- appearances in crater 
of1 #af    -- -- at night1 #aj    --    
compared with ,vesuvius1 #bc    --      
crater of1 #ac    -- dependence of      
eruptions on atmospheric conditions1 #cd
    -- eruption of1 #ad1 fig4 #d    --  
general features of1 #aa    -- map of1  
#aa1 fig4 #b    -- observations by      
,spallanzani1 #h    -- resemblance to   
flashing light1 #aj    -- section of1   
#ac1 fig4 #h    -- soundings around1 #ab
    -- vapour-cloud above1 #i    --     
violent eruptions of1 #bc               
,strombolian stage1 #bc    ,stufas1     
nature of1 #bag    ,submarine volcanoes1
 #agi    ,subterranean forces1          
beneficial effects of1 #cjc             

,subsidence in centre of volcanoes1 #afe
    ,sulphur1 absorption of water by    
molten1 #cef    -- deposited on         
lava-streams1 #aaj    -- how formed at  
volcanoes1 #ah    -- not the cause of   
volcanic outbursts1 #ah    ,surfaces of 
lava-streams1 #ig-ii1 figs4 #bb1 #bc    
,sun-spots1 #cfa-cfc1 figs4 #hi1 #ij1   
#ia    ,syenite1 #ei    ,syssiderites1  
#caf    ,szabo1 ,professor1 cited1 #aii 
,,tachylyte1 #ei    ,tertiary volcanoes 
of ,british ,islands1 #bgf    ,terraces1
 sinter- and travertine-formation of1   
#ahe1 fig4 #hj    ,temperature1 increase
 in deeper parts of earth's crust1 #cce 
-- rate of increase in different areas1 
#cdj    ,teneriffe1 #dd1 #aea           
,teneriffe1 #agh1 fig4 #gg    -- peak   
of1 #age1 fig4 #gc    ,tenon-and-mortise
 structure in basaltic columns1 #ajg    
,theodosius and ,vulcano1 #c            
,thunder1 accompanying volcanic         
outbursts1 #bh    ,trachytes1 #di1 #ej1 
#fi    ,trap-rocks1 origin of1 #bda     
,trass1 #ij    ,travertine or           

,tibur-stone1 #ahd    -- deposits of1   
#bbj    ,triassic volcanoes of ,british 
,islands1 #bge    ,tridymite deposited  
on lava-streams1 #aaj    ,troilite1 #cad
    ,troost1 cited1 #cee    ,tufa1 or   
tuff1 #ij    ,tuff-cones1 character of1 
#aeg    -- denudation of1 #aeg1 #aeh    
,typhon1 fable of1 #c                   
,,ultra-,,basic lavas1 #ej1 #ff    --   
rocks1 #cag      ,,val ,,del ,,bove1    
,etna1 #acc1 #ahj1 #bji    -- -- dykes  
in1 #acd1 fig4 #ee    ,vapour-cloud over
 ,vesuvius1 #bf1 #bi    -- --           
,stromboli1 #i    ,ventotienne1 ,island 
of1 section at1 #acj1 fig4 #di          
,vesuvius1 #cg    -- changes in form of1
 #ha    -- compared with ,stromboli1 #bc
    -- crater of in #agef1 #hd1 fig4 #ad
    -- -- of in #agfg1 #he1 fig4 #af    
-- -- of in #ahbb1 #hb1 fig4 #ac    --  
-- of in #ahdc1 #hf1 fig4 #af    --     
detonations at1 #bf    -- early history 
of1 #hc    -- eruption of year #gi1 #hd 
-- -- of #ahbb1 #fi    -- -- of ,april  
#ahgb1 #bd    -- -- of ,october #ahbb1  

#bd    -- ejected blocks of1 #de    --  
first eruption of1 #g    -- form of1    
#aff    -- fossils of1 #de    -- growth 
of cone of1 #hj    -- history of1 #bjd  
-- last eruption of1 #g    --           
lava-stream of #ahee1 #aja    --        
lava-streams of #aheh1 #ahgb1 #ig    -- 
lavas of1 #ajd    -- minerals of1 #df   
-- -- ejected at1 #adi    -- observatory
 on1 #bd1 #cg    -- outlines of1 #hg    
-- pine-tree appendage of1 #bi    --    
scoria-cones in lava1 #abb    -- -- on  
lava of #ahee1 #aec    -- steam emitted 
by lava of1 #bg    -- vapour-cloud over1
 #bf1 #bi    ,vesuvian stage1 #bc    -- 
eruption1 photograph of1 #bd1 fig4 #e   
,viscid lavas of ,lipari ,islands1      
#id-if    ,vitreous lavas1              
devitrification of1 #bei    ,volcanic   
action1 laws of1 #cb    -- bombs1 #gj1  
#ga    -- cycles1 nature of1 #bba1 #bbb 
-- -- duration of1 #bbc    -- cones1    
internal structure of1 #aae-abb    -- --
 experimental illustration of formation 
of1 #abj1 fig4 #cg    -- -- limits to   

height of1 #aff    -- -- form of1 #aeb  
-- -- dimensions of1 #aeb    -- --      
irregular development of1 #ij    -- --  
slopes of sides of1 #ia    -- --        
composed of ejected rock-fragments1 #aef
    -- -- curved slopes of1 #aef    --  
dbris on sea-bottom1 #bdj    -- dust1   
fineness of1 #fi    -- districts1 areas 
of upheaval1 #bde    -- ejections1      
alteration of1 #beh    -- eruptions1    
compared to ebullition1 #ai1 #bj    --  
forces1 compensate for denudation1 #bhc 
-- -- intensity at former periods1 #bgh 
-- -- necessity for action of1 #bhe     
-- -- shifting of from one area to      
another1 #bgg    -- mountains1 origin of
 conical forms1 #hi    -- -- mode of    
growth1 #hi    -- phenomena of the past 
similar to those at present1 #bgc    -- 
products1 order of appearance of1 #aih1 
#aii    ,volcanic rocks1 #fa    -- --   
similarity of ancient and modern1 #bec  
,volcano1 origin of name1 #c    --      
craters of1 #afg    -- ,island of4 ,see 
,vulcano4    -- compared to             

steam-engine1 #h    ,volcanoes1 blocks1 
ejected from1 #de    -- built up of     
ejected fragments1 #gd    -- destruction
 caused by1 #bha    -- dissected by     
denudation1 #aae1 #aci    -- erroneous  
ideas concerning1 #a    -- ejection of  
different materials from1 #bje    --    
known to ancients1 #c    -- life-history
 of1 #ahf    -- number of1 #bbd1 #bbe   
-- of ,africa1 #bbg    -- of ,america1  
#bcf    -- of ,asia1 #bcf    -- of      
,bohemia1 #abf    -- of ,central ,asia1 
#bcf    -- of ,central ,pacific1 #bcf   
-- of ,europe1 #bbg    -- of ,hungary1  
#abf    -- position in relation to      
mountain chains1 #bdc    -- popular     
ideas concerning1 #a    -- reservoirs   
beneath1 #ade    ,volvic lava of1 #ajc  
,vose1 cited1 #cdf    ,vulcan1 forge of1
 #c    ,vulcano1 island of1 #c1 #aeh    
,vulcano and ,theodosius1 #c            
,vulcano1 #agh1 fig4 #gg    -- and      
,vulcanello1 view of1 #dc1 fig4 #f    --
 chemical deposits at1 #dd    --        
eruption in #aghf1 #dc    -- -- in      

#ahgc1 #dc    -- -- lava-stream in1 #ie1
 fig4 #ai    -- --1 #ajc1 fig4 #bg    --
 plan of1 #aie1 fig4 #he    -- section  
of volcanic cone in1 #aaf1 fig4 #ce     
-- section in1 #abi    -- shifting of   
centre of eruption in1 #aif             
,vulcanello1 craters of1 #aig1 fig4 #hf 
,vulcanology1 origin of the science1 #d 
-- earliest treatise on1 #e             
,walferdin1 ,m41 cited1 #cdj    ,water  
in lavas1 #cec    -- penetration through
 rocks1 #ceh    -- presence of in lavas1
 #ajb    -- and saline solutions in     
cavities of crystals1 #fc    ,werner1   
cited1 #bja    ,western ,isles of       
,scotland1 #ajc1 #aci1 #adb    -- --    
volcanoes of1 #bab    ,whymper1 ,mr41   
#fi    ,woodward1 ,mr41 experiments of1 
#aai    ,wrekin1 ancient volcanic rocks 
of1 #bei      ,,young1 ,professor1      
cited1 #cfe      ,,zeolites1 formation  
of1 #aej                                
,,printed ,,by                          
,,spottiswoode ,,and ,,co4 ,,ltd41      
,,new-,,street ,,square                 

,,london                                
,,the                                   
,,international ,,scientific ,,series4  
,each ,book ,complete in ,one ,volume4  
,crown #hvo4 cloth1 #es4                
unless otherwise described4      ,i4    
,,forms of ,,water3 in ,clouds and      
,rivers1 ,ice and ,glaciers4 ,by ,j4    
,tyndall1 ,,ll4,d41 ,f4,r4,s4 ,with #bf 
,illustrations4 ,twelfth ,edition4      
,,ii4 ,,physics and ,,politics2 or1     
,thoughts on the ,application of        
the ,principles of ',natural ,selection'
 and ',inheritance' to                  
,political ,society4 ,by ,walter        
,bagehot4 ,tenth ,edition4      ,,iii4  
,,foods4 ,by ,edward ,smith1 ,m4,d41    
,l4,l4,b41 ,f4,r4,s4 ,with #aef         
,illustrations4 ,tenth ,edition4        
,,iv4 ,,mind and ,,body3 the ,theories  
of their ,relation4 ,by ,alexander      
,bain1 ,,ll4,d4 ,with ,four             
,illustrations4 ,ninth ,edition4        
,v4 ,the ,,study of ,,sociology4 ,by    
,herbert ,spencer4 ,eighteenth ,edition4

      ,,vi4 ,the ,,conservation of      
,,energy4 ,by ,balfour ,stewart1 ,m4,a41
 ,,ll4,d41         ,f4,r4,s4 ,with #ad  
,illustrations4 ,eighth ,edition4       
,,vii4 ,,animal ,,locomotion2 or1       
,walking1 ,swimming1 and ,flying4 ,by   
,j4 ,b4         ,pettigrew1 ,m4,d41     
,f4,r4,s41 c4 ,with #acj ,illustrations4
 ,fourth         ,edition4      ,,viii4 
,,responsibility in ,,mental ,,disease4 
,by ,henry ,maudsley1 ,m4,d4            
,fifth ,edition4      ,,ix4 ,the ,,new  
,,chemistry4 ,by ,professor ,j4 ,p4     
,cooke1 of the ,harvard                 
,university4 ,with #ca ,illustrations4  
,eleventh ,edition4      ,x4 ,the       
,,science of ,,law4 ,by ,professor      
,sheldon ,amos4 ,eighth ,edition4       
,,xi4 ,,animal ,,mechanism3 a ,treatise 
on ,terrestrial and ,arial              
,locomotion4 ,by ,professor ,r4 ,j4     
,marey4 ,with #aag ,illustrations4      
,fourth ,edition4      ,,xii4 ,the      
,,doctrine of ,,descent and ,,darwinism4
 ,by ,professor ,oscar         ,schmidt 

7,strasburg ,university74 ,with #bf     
,illustrations4 ,eighth                 
,edition4      ,,xiii4 ,the ,,history of
 the ,,conflict between ,,religion and  
,,science4 ,by         ,j4 ,w4 ,draper1 
,m4,d41 ,,ll4,d4 ,twenty-second         
,edition4      ,,xiv4 ,,fungi3 their    
,nature1 ,influences1 ,uses1 c4 ,by ,m4 
,c4 ,cooke1         ,m4,a41 ,,ll4,d4    
,edited by the ,rev4 ,m4 ,j4 ,berkeley1 
,m4,a41 ,f4,r4,s4         ,with         
,illustrations4 ,fifth ,edition4        
,,xv4 ,the ,,chemistry of ,,light and   
,,photography4 ,by ,dr4 ,hermann ,vogel4
         ,with #ajj ,illustrations4     
,sixth ,edition4      ,,xvi4 ,the ,,life
 and ,,growth of ,,language4 ,by        
,william ,dwight ,whitney4              
,sixth ,edition4      ,,xvii4 ,,money   
and the ,,mechanism of ,,exchange4 ,by  
,w4 ,stanley ,jevons1         ,m4,a41   
,f4,r4,s4 ,eleventh ,edition4           
,,xviii4 ,the ,,nature of ,,light1 with 
a ,general ,account of ,,physical       
,,optics4 ,by ,dr4 ,eugene ,lommel4     

,with #ahh ,illustrations and a         
,table of ,spectra ,in                  
,chromo-lithography4 ,sixth ,edition4   
,,xix4 ,,animal ,,parasites and         
,,messmates4 ,by ,monsieur ,van         
,beneden4 ,with         #hh             
,illustrations4 ,fourth ,edition4       
,london3 ,,kegan ,,paul1 ,,trench1      
,,tr,,bner1  ,,co41 ,ltd4               
,the ,international ,scientific         
,series--continued4      ,,xx4          
,,fermentation4 ,by ,professor          
,schtzenberger4 ,with #ih               
,illustrations4 ,fourth ,edition4       
,,xxi4 ,the ,,five ,,senses of ,,man4   
,by ,professor ,bernstein4 ,with #ia    
,illustrations4 ,seventh ,edition4      
,,xxii4 ,the ,,theory of ,,sound in its 
,,relation to ,,music4 ,by ,professor   
,pietro ,blaserna4 ,with numerous       
,illustrations4 ,sixth ,edition4        
,,xxiii4 ,,studies in ,,spectrum        
,,analysis4 ,by ,j4 ,norman ,lockyer1   
,f4,r4,s4         ,with ,six            
,photographic ,illustrations of         

,spectra1 and numerous                  
,engravings on ,wood4 ,fifth ,edition4  
#fs1 #f;d4      ,,xxiv4 ,a ,,history of 
the ,,growth of the ,,steam ,,engine4   
,by ,professor ,r4         ,h4          
,thurston4 ,with numerous               
,illustrations4 ,fifth ,edition4        
,,xxv4 ,,education as a ,,science4 ,by  
,alexander ,bain1 ,,ll4,d4 ,ninth       
,edition4      ,,xxvi4 ,the ,,human     
,,species4 ,by ,professor ,a4 de        
,quatrefages1 ,membre de                
l',institut4 ,fifth ,edition4           
,,xxvii4 ,,modern ,,chromatics4 ,with   
,application to ,art and ,industry4 ,by 
,ogden ,n4 ,rood4 ,third ,edition4 ,with
 #acj original ,illustrations4          
,,xxviii4 ,the ,,crayfish3 an           
,introduction to the ,study of ,zoology4
 ,by         ,t4 ,h4 ,huxley1 ,f4,r4,s4 
,sixth ,edition4 ,with #hc              
,illustrations4      ,,xxix4 ,the       
,,brain as an ,,organ of ,,mind4 ,by ,h4
 ,charlton ,bastian1 ,m4,d4             
,fourth ,edition4 ,with #ahd            

,illustrations4      ,,xxx4 ,the        
,,atomic ,,theory4 ,by ,professor ,a4   
,wurtz4 ,translated by ,e4              
,cleminshaw1 ,f4,r4,s4 ,seventh         
,edition4      ,,xxxi4 ,the ,,natural   
,,conditions of ,,existence as they     
affect ,animal         ,life4 ,by ,karl 
,semper4 ,fifth ,edition4 ,with #c ,maps
 and #ajf         ,woodcuts4            
,,xxxii4 ,,general ,,physiology of      
,,muscles and ,,nerves4 ,by ,prof4 ,j4  
,rosenthal4 ,fourth ,edition4 ,with #ge 
,illustrations4      ,,xxxiii4 ,,sight3 
an ,exposition of the ,principles of    
,monocular and         ,binocular       
,vision4 ,by ,joseph ,le ,conte1        
,,ll4,d4 ,third ,edition4         ,with 
#acb ,illustrations4      ,,xxxiv4      
,,illusions3 a ,psychological ,study4   
,by ,james ,sully4 ,fourth              
,edition4      ,,xxxv4 ,,volcanoes3 what
 they are and what they teach4 ,by ,john
 ,w4         ,judd1 ,f4,r4,s4 ,fifth    
,edition4 ,with #if ,illustrations4     
,,xxxvi4 ,,suicide3 an ,essay on        

,comparative ,moral ,statistics4 ,by    
,professor ,h4 ,morselli4 ,third        
,edition4      ,,xxxvii4 ,the ,,brain   
and its ,,functions4 ,by ,j4 ,luys1     
,physician to the         ,hospice de la
 ,salptrire4 ,with numerous             
,illustrations4 ,third         ,edition4
      ,,xxxviii4 ,,myth and ,,science3  
an ,essay4 ,by ,tito ,vignoli4 ,fourth  
,edition4      ,,xxxix4 ,the ,,sun4 ,by 
,c4 ,a4 ,young1 ,ph4,d41 ,,ll4,d4 ,fifth
 ,edition4 ,with         numerous       
,illustrations4      ,,xl4 ,,ants1      
,,bees1 and ,,wasps4 ,a ,record of      
,observations on the ,habits         of 
the ,social ,hymenoptera4 ,by ,sir ,john
 ,lubbock1 ,bart41 ,m4,p4               
,fourteenth ,edition4 ,with #e          
,chromo-lithographic ,plates4           
,,xli4 ,,animal ,,intelligence4 ,by     
,george ,j4 ,romanes4 ,,ll4,d41         
,f4,r4,s4 ,sixth         ,edition4      
,,xlii4 ,the ,,concepts and ,,theories  
of ,,modern ,,physics4 ,by ,j4 ,b4      
,stallo4         ,third ,edition4       

,london3 ,,kegan ,,paul1 ,,trench1      
,,tr,,bner1  ,,co41 ,ltd4               
,the ,international ,scientific         
,series--continued4      ,,xliii4       
,,diseases of ,,memory4 ,an ,essay in   
the ,positive ,psychology4 ,by          
,th4 ,ribot4 ,fourth ,edition4          
,,xliv4 ,,man ,,before ,,metals4 ,by ,n4
 ,joly1 ,correspondent de l',institut de
         ,france4 ,fifth ,edition4 ,with
 #adh ,illustrations4      ,,xlv4 ,the  
,,science of ,,politics4 ,by ,prof4     
,sheldon ,amos4 ,third ,edition4        
,,xlvi4 ,,elementary ,,meteorology4 ,by 
,robert ,h4 ,scott4 ,with #aa ,plates   
and #dj ,figures in ,text4 ,seventh     
,edition4      ,,xlvii4 ,the ,,organs of
 ,,speech4 ,by ,georg ,hermann von      
,meyer4 ,with #dg                       
,illustrations4      ,,xlviii4          
,,fallacies3 a ,view of ,logic from the 
,practical ,side4 ,by         ,alfred   
,sidgwick4 ,second ,edition4            
,,xlix4 ,the ,,origin of ,,cultivated   
,,plants4 ,by ,alphonse ,de ,candolle4  

,second ,edition4      ,l4 ,,jelly      
,,fish1 ,,star ,,fish1 and ,,sea        
,,urchins4 ,being a ,research on        
,primitive ,nervous ,systems4 ,by ,g4   
,j4 ,romanes1 ,,ll4,d41 ,f4,r4,s4       
,second ,edition4      ,,li4 ,the       
,,common ,,sense of the ,,exact         
,,sciences4 ,by the late ,william       
,kingdon ,clifford4 ,third ,edition4    
,with #ajj ,figures4      ,,lii4        
,,physical ,,expression3 its ,modes and 
,principles4 ,by ,francis               
,warner1 ,m4,d41 ,f4,r4,c4,p4 ,second   
,edition4 ,with #ej ,illustrations4     
,,liii4 ,,anthropoid ,,apes4 ,by ,robert
 ,hartmann4 ,with #fc ,illustrations4   
,second ,edition4      ,,liv4 ,the      
,,mammalia in their ,,relation to       
,,primeval ,,times4 ,by ,oscar          
,schmidt4 ,second ,edition4 ,with #ea   
,woodcuts4      ,,lv4 ,,comparative     
,,literature4 ,by ,h4 ,macaulay         
,posnett1 ,,ll4,d4      ,,lvi4          
,,earthquakes and other ,,earth         
,,movements4 ,by ,prof4 ,john ,milne4   

,with #hh ,figures4 ,fourth ,edition1   
revised4      ,,lvii4 ,,microbes1       
,,ferments1 and ,,moulds4 ,by ,e4 ,l4   
,trouessart4 ,with #ajg                 
,illustrations4 ,third ,edition4        
,,lviii4 ,,geographical and ,,geological
 ,,distribution of ,,animals ,by ,prof4 
,a4 ,heilprin4 ,second ,edition4        
,,lix4 ,,weather3 a ,popular ,exposition
 of the ,nature of ,weather ,changes    
from ,day to ,day4 ,by the ,hon4 ,ralph 
,abercromby4 ,with #if         ,figures4
 ,fourth ,edition4      ,,lx4 ,,animal  
,,magnetism4 ,by ,alfred ,binet and     
,charles ,fre4 ,fourth         ,edition4
      ,,lxi4 ,,manual of ,,british      
,,discomycetes1 with descriptions of all
 the         ,species of ,fungi hitherto
 found in ,britain included in the      
,family1 and ,illustrations of the      
,genera4 ,by ,william ,phillips1        
,f4,l4,s4 ,second ,edition4      ,,lxii4
 ,,international ,,law4 ,with ,materials
 for a ,code of ,international          
,law4 ,by ,professor ,leone ,levi4      

,,lxiii4 ,the ,,geological ,,history of 
,,plants4 ,by ,sir ,j4 ,william ,dawson4
         ,with #hj ,illustrations4      
,,lxiv4 ,the ,,origin of ,,floral       
,,structures ,,through ,,insect and     
other         ,,agencies4 ,by ,prof4 ,g4
 ,henslow4 ,second ,edition4      ,,lxv4
 ,on the ,,senses1 ,,instincts1 and     
,,intelligence of ,,animals1 with       
special reference to ,,insects4 ,by ,sir
 ,john ,lubbock1 ,bart41 ,m4,p4         
,with #aah ,illustrations4 ,third       
,edition4               ,london3 ,,kegan
 ,,paul1 ,,trench1 ,,tr,,bner1  ,,co41  
,ltd4                 ,the              
,international ,scientific              
,series--continued4      ,,lxvi4 ,the   
,,primitive ,,family in its ,,origin and
 ,,development4 ,by ,c4 ,n4             
,starcke4 ,second ,edition4             
,,lxvii4 ,,physiology of ,,bodily       
,,exercise4 ,by ,fernand ,lagrange1     
,m4,d4         ,second ,edition4        
,,lxviii4 ,the ,,colours of ,,animals3  
their ,meaning and ,use1 especially     

considered in the case of ,insects4 ,by 
,e4 ,b4 ,poulton1 ,f4,r4,s4             
,with ,chromolithographic ,frontispiece 
and upwards of #fj ,figures         in  
,text4 ,second ,edition4      ,,lxix4   
,,introduction to ,,fresh-,,water ,,alg4
 ,with an ,enumeration of all           
the ,british ,species4 ,by ,m4 ,c4      
,cooke1 ,,ll4,d4 ,with #ac ,plates      
,illustrating all the ,genera4          
,,lxx4 ,,socialism3 ,,new and ,,old4 ,by
 ,william ,graham1 ,m4,a41 ,professor of
         ,political ,economy and        
,jurisprudence1 ,queen's ,college1      
,belfast4         ,second ,edition4     
,,lxxi4 ,,colour-,,blindness and        
,,colour-,,perception4 ,by ,f4 ,w4      
,edridge-,green1 ,m4,d4 ,with #c        
,coloured ,plates4      ,,lxxii4 ,,man  
and the ,,glacial ,,period4 ,by ,g4 ,f4 
,wright1 ,d4,d4 ,with #aaa              
,illustrations and ,maps4 ,second       
,edition4      ,,lxxiii4 ,,handbook of  
,,greek and ,,latin ,,pal,,ography4 ,by 
,sir ,e4 ,maunde         ,thompson1     

,k4,c4,b4 ,with ,tables of ,alphabets   
and ,facsimiles4         ,second        
,edition4      ,,lxxiv4 ,a ,,history of 
,,crustacea3 ,recent ,malacostraca4 ,by 
,thomas ,r4 ,r4         ,stebbing1      
,m4,a4 ,with #ai ,plates and #cb        
,figures in ,text4      ,,lxxv4 ,the    
,,dispersal of ,,shells3 an ,inquiry    
into the means of         ,dispersal    
possessed by ,fresh ,water and ,land    
,mollusca4 ,by ,h4         ,wallis ,kew1
 ,f4,z4,s4 ,with ,preface by ,a4 ,r4    
,wallace1 ,f4,b4,s41 and                
,illustrations4      ,,lxxvi4 ,,race and
 ,,language4 ,by ,andr ,lefvre1         
,professor in the                       
,anthropological ,school1 ,paris4       
,,lxxvii4 ,the ,,origin of ,,plant      
,,structures by ,,self-,,adaptation ,,to
 ,,the         ,,environment4 ,by ,rev4 
,g4 ,henslow4 ,m4,a41 ,f4,l4,s41        
,f4,g4,s41 c41         author of ',the  
,origin of ,floral ,structures1' c4     
,,lxxviii4 ,,ice-,,work ,,present and   
,,past4 ,by ,rev4 ,t4 ,g4 ,bonney1      

,d4,sc41         ,,ll4,d41 ,f4,r4,s41   
c41 ,professor of ,geology at           
,university         ,college1 ,london2  
,fellow of ,st4 ,john's ,college1       
,cambridge4      ,,lxxix4 ,a            
,,contribution to our ,,knowledge of    
,,seedlings4 ,by ,rt4 ,hon4         ,sir
 ,john ,lubbock1 ,bart41 ,m4,p41        
,f4,r4,s4      ,,lxxx4 ,the ,,art of    
,,music4 ,by ,sir ,c4 ,hubert ,h4       
,parry1 ,mus4 ,doc4      ,,lxxxi4 ,the  
,,polar ,,aurora4 ,by ,alfred ,angot4   
,illustrated4      ,,lxxxii4 ,,what is  
,,electricity8 ,by ,j4 ,trowbridge4     
,illustrated4      ,,lxxxiii4 ,,memory4 
,by ,f4 ,w4 ,edridge-,green1 ,m4,d4     
,with ,frontispiece4      ,,lxxxiv4 ,the
 ,,elements of ,,hypnotism4 ,by ,b4     
,harry ,vincent4 ,with                  
,diagrams4 ,second ,edition4            
,,lxxxv4 ,,seismology4 ,by ,john ,milne1
 ,f4,r4,s41 ,f4,g4,s41 c41 ,author of   
',earthquakes4' ,with #fc ,figures4     
,,lxxxvi4 ,on ,,buds and ,,stipules4 ,by
 the ,right ,hon4 ,sir ,john ,lubbock1  

,bart1 ,m4,p41 ,f4,r4,s41 ,d4,c4,l41    
,,ll4,d4 ,with #d ,coloured ,plates and 
#cdj ,figures in the ,text4             
,,lxxxvii4 ,,evolution by ,,atrophy1 in 
,biology and ,sociology4 ,by ,jean      
,demoor1 ,jean ,massart1 and ,emile     
,vandervelde4 ,translated by            
,mrs4 ,chalmers ,mitchell4 ,with #hd    
,figures4               ,london3 ,,kegan
 ,,paul1 ,,trench1 ,,tr,,bner1  ,,co41  
,ltd4             99       99       99  
99       99      ,transcriber ,note     
,minor typos corrected4 ,listing of ,the
 ,international ,scientific ,series  was
 split between the front and end of book
 but are here moved to the  end4 ,the   
list was also reformatted4 ,the captions
 for the map key in  ,figure #eh were   
reformatted into a table4 ,figure #da   
was relocated as it  followed ,figure   
#db in the printed version4