,transcriber ,note ,text emphasis denoted as ,italics and ,bold4 ,whole and fractional numbers as #abc-d_/e4 ,the ,cambridge ,manuals of ,science and ,literature ,,rocks ,,and ,,their ,,origins ,,cambridge ,,university ,,press ,london3 ,,fetter ,,lane1 ,e4,c4 ,c4 ,f4 ,,clay1 ,manager ,illustration ,edinburgh3 #ajj1 ,,princes ,,street ,london3 ,,william ,,wesley ,,son1 #bh1 ,,essex ,,street1 ,,strand ,berlin3 ,a4 ,,asher ,,and ,,co4 ,leipzig3 ,f4 ,a4 ,,brockhaus ,new ,york3 ,g4 ,p4 ,,putnam',s ,,sons ,bombay and ,calcutta3 ,,macmillan ,,and ,,co41 ,ltd4 ,all rights reserved ,,rocks ,,and ,,their ,,origins ,,by ,,grenville ,a4 ,j4 ,,cole ,professor of ,geology in the ,royal ,college of ,science for ,ireland ,cambridge3 at the ,university ,press #aiab ,cambridge3 ,,printed ,,by ,,john ,,clay1 ,m4,a4 ,,at ,,the ,,university ,,press ,with the exception of the coat of arms at the foot1 the design on the title page is a reproduction of one used by the earliest known ,cambridge printer1 ,john ,siberch1 #aeba ,,preface ,this little book is intended for those who are not specialists in geology1 and it may perhaps be accepted as a contribution for the general reader4 ,to all who are interested in the earth1 the study of rocks is an important branch of natural history4 ,if detailed works on petrology are to be consulted later1 ,f4 ,w4 ,clarke's ,data of ,geochemistry 7,bulletin1 ,u4,s4 ,geological ,survey1 ed4 #b1 #aiaa7 must on no account be overlooked4 ,its numerous references to published papers1 and the attention given to rock-origins1 make it a worthy companion to ,c4 ,doelter's ,petrogenesis4 ,many things have perforce been omitted from the present essay4 ,it seemed unnecessary to review the ,carbonaceous rocks1 since the most important of these have been admirably dealt with in ,e4 ,a4 ,n4 ,arber's ,natural ,history of ,coal1 published as a volume in this series4 ,i should like to have described occurrences of rock-salt1 of massive gypsum1 and other products of arid lands1 where black alkali poisons the surface1 and the casual pools are fringed with white and crumbling crusts4 ,rock-taluses1 and all the varied alluvium carried seaward as the outwash of continental land1 well deserve a chapter to themselves4 ,but there is really no end to the subject1 which embraces all the accumulative processes of the earth4 ,a few vacation-journeys1 judiciously planned out1 teach us that text-books are merely signposts to set us on what is believed to be the way4 ,when the path enters the great forest1 or rises above green lakelets to the crags1 we find there those who went before us1 pointing to unconquered lands4 ,g4 ,a4 ,j4 ,c4 ,royal ,college of ,science for ,ireland1 ,dublin4 ,february #aiab4 ,,contents ,,chap4 ,,page ,list of ,illustrations viii ,i4 ,on ,rocks in ,general #a ,list of the common ,minerals that form ,rocks #h ,,ii4 ,the ,limestones #ab ,,iii4 ,the ,sandstones #ef ,,iv4 ,clays1 ,shales1 and ,slates #gh ,v4 ,igneous ,rocks #ajc ,,vi4 ,metamorphic ,rocks #adc ,references #afb ,table of ,stratigraphical ,systems #ahi ,index #agj ,,list ,,of ,,illustrations ,,fig4 ,,page #a ,surface of ,limestone plateau1 ,causse du ,larzac1 ,aveyron #de #b ,ravine in ,limestone1 ,caon of the ,dourbie1 ,aveyron #dg #c ,waterworn cliff of ,limestone1 ,millersdale #di #d ,limestone country dissected by ravines1 ,hercegovina #ea #e ,sand developing from ,sandstone1 ,cape of ,good ,hope #ei #f ,siliceous ,conglomerate1 ,co4 ,waterford #ge #g ,quartzite ,cone1 ,croagh ,patrick #gg #h ,shrinkage-cracks in ,clay1 ,spitsbergen #ha #i ,landslide of ,limestone over ,shale1 ,drme #ic #aj ,weathering of ,shale1 ,isre #ie #aa ,boulder-clay1 ,crich1 ,derbyshire 7,phot4 ,h4 ,a4 ,bemrose7 #ig #ab ,nordenskild ,glacier1 ,spitsbergen #ii #ac ,sefstrm ,glacier1 ,spitsbergen #aja #ad ,ash-layer of #aijf on ,vesuvius #aaa #ae ,puy de la ,vache1 ,puy-de-,dme #aac #af ,granite invading ,mica-schist1 ,cape ,town #aba #ag ,weathering granite1 ,lundy ,island #aci #ah ,granite weathering under tropical conditions1 ,matopo ,hills #ada #ai ,composite ,gneiss1 ,co4 ,donegal #aec #bj ,composite ,gneiss1 ngn1 ,sweden #aee 7,figs4 #aa and #ag are reproduced from the ,cambridge ,county ,geographies of ,derbyshire and ,devonshire respectively2 the rest of the illustrations are from photographs by the author47 ,,chapter ,i ,,on ,,rocks ,,in ,,general ,the description of rocks has fallen very much into the hands of lovers of analysis and classification1 and attention has been diverted1 even among geologists1 from their fundamental importance as parts of the earth's crust4 ,the geographer or the general traveller may often wish for closer acquaintance with the units that build up the scenery around him4 ,the characters of rocks again and again control the features of the landscape4 ,when studied more nearly1 these same characters imply conditions of deposition or solidification1 and lead the mind back to still older landscapes1 and to the meeting of oceans and continents on long-forgotten shores4 ,petrology1 indeed1 involves the understanding of how rocks come to be where we find them when we try2 but the classification of hand-specimens was from the first easier than field-investigation1 and in later times the science was threatened with the description of isolated microscopic slides4 ,fortunately1 a certain amount of feeling for natural history has been imported again into the subject1 and evolutionary principles and sequences have been discussed4 ,experimental work1 moreover1 has been brought to bear on the question of the origins of rocks1 with more success than might have been expected1 since it is very difficult to realise in a laboratory1 or even in the mind1 the conditions that prevail in the lower parts of the earth's crust4 ,rocks1 we have to remember1 are in themselves considerable masses1 and have relations with others far away4 ,the coarseness of a sandstone at one point1 or even over square miles of country1 implies the deposition of finer material somewhere else4 ,the lava-flow implies the existence of mysterious cauldrons in the crust4 ,it is1 however1 fortunate that the primary classification of rocks was promulgated without regard for theories of rock-origins4 ,the work was done by men who were masters and pioneers in mineralogy4 ,at a time when a powerful school regarded basalt as of sedimentary origin1 and when granite was generally believed to be the most ancient component of the crust1 rock-masses were taken in hand as aggregates of certain minerals1 and were reduced to an orderly scheme for arrangement in the cabinets of the curious4 ,any system based on ideal relationships would have been fatal at that time to petrology as a science4 ,alexandre ,brongniart1 in #ahac1 thus saw objections to the classification of rocks that had been proposed by ,werner4 ,in his ,essai d'une classification minralogique des ,roches mlanges1 he showed the impossibility of determining the age of a rock in relation to others before assigning to it a name1 and the absurdity of separating similar rocks on account of differences in their geological age4 ,brongniart was thus forced to rely1 firstly1 upon the prevalence of certain mineral constituents1 and1 secondly1 on the structure of the mass4 ,he developed this scheme in #ahbg1 in his ,classification et caractres minralogiques des ,roches homognes et htrognes2 but it is clear that1 even in such a system1 considerations of natural history and of origin will ultimately predominate4 ,brongniart was much influenced by ,karl von ,leonhard's ,charakteristik der ,felsarten1 published in #ahbc1 and these two authors have been regarded as the founders of petrography4 ,the difficulty of distinguishing between rocks laid down as true sediments on the earth's surface and those that have consolidated from a state of fusion has been very largely removed4 ,the assistance of the microscope can now be called on to elucidate the minute structure of fine-grained masses1 which appeared homogeneous to earlier workers4 ,the pioneer in microscopic methods was ,pierre ,louis ,antoine ,cordier1 who knew rocks as a traveller knows them in the field4 ,in #agih1 as a young man of twenty-one1 he had gone to ,egypt with the famous expedition under ,general ,bonaparte4 ,dodat de ,dolomieu had charge of the geological observations1 and ,cordier went through the hardships of the campaign as his assistant4 ,when ,bonaparte abandoned the army and withdrew to ,paris1 ,cordier might well have been lost to ,europe4 ,however1 he successfully brought home the knowledge acquired in the field1 and set himself1 in those agitating years1 to solve the problem of the compact groundwork of igneous rocks4 ,he argued that this groundwork probably consisted of minerals1 and that these minerals were probably similar to those occurring as visible constituents of the mass4 ,he examined the powder of these larger crystals under the microscope1 and made himself familiar with their aspect in a fractured form4 ,he then powdered the compact material of his rocks1 washed away the dust1 and was able to recognise in the coarser residue the minerals that he had previously studied4 ,he used the magnet to extract the iron ore2 he determined the fusibility of the particles with the blowpipe2 and he even discovered in volcanic lavas a residual glass associated with the crystalline material#a4 ,to this day1 when a particular mineral has to be determined in a rock1 it is often best to follow ,cordier's method1 and to extract the actual crystals1 however small4 ,various modes of separation1 especially those involving the use of dense liquids1 have been devised since ,cordier's time1 and the specific gravity of a single crystal can now be determined1 although it may be so small as to require looking for in the dense liquid with a lens#b4 ,between #ahcf and #ahch1 ,christian ,gottfried ,ehrenberg1 ,professor of ,medicine at ,berlin1 made an immense step forward in the study of rocks4 ,being keenly interested in microscopic forms of life1 he wished to determine their importance as constituents of rocks4 ,using a microscope magnifying #cjj diameters1 he showed the presence of organisms in flint and limestone1 and found in #ahch that a thin slice of chalk coated over with ,canada balsam became practically transparent4 ,in his ,mikrogeologie1 published in #ahed1 he gives drawings of thin sections of several flints1 seen by transmitted light1 which are thus rock-sections in the modern petrological sense4 ,his method could not have been generally known until his book appeared in #ahed4 ,meanwhile1 ,henry ,clifton ,sorby1 about #ahde1 found the naturalist ,w4 ,c4 ,williamson making thin sections of fossil plants and bones4 ,he promptly perceived the importance of the method as applied to rocks in general1 and introduced it to the ,geological ,society of ,london in #ahej1 in a paper on the ,calcareous ,grit of ,scarborough4 ,seven years later1 he read his memorable paper on ,the ,microscopical ,structure of ,crystals#c1 in which he made use of slices of granite and of ,vesuvian and other lavas4 ,ferdinand von ,zirkel met ,sorby by chance at ,bonn in #ahfb1 and1 learning his methods1 proceeded to systematise the examination of rock-specimens with the microscope4 ,such studies1 rapidly appreciated by ,michel ,lvy1 ,rosenbusch1 ,judd1 and others1 naturally led to advances of the first importance in petrology4 ,they enabled workers to ascertain the relations of the rock-constituents one to another1 and the order of consolidation of minerals from an igneous magma4 ,the broad division of rocks into those of sedimentary and those of igneous origin has been further emphasised4 ,the rocks styled metamorphic still afford the greatest difficulty1 even after prolonged enquiry in the field4 ,seeing that some rocks are merely massive minerals1 that is1 large masses formed of one mineral species1 while others consist of crystals or fragments of a variety of minerals1 it may be well to remind ourselves of the distinction between minerals and rocks4 ,we may define a mineral as a natural substance formed by inorganic action2 its chemical composition is constant2 under favourable circumstances1 it assumes a characteristic crystalline form4 ,like all definitions of natural objects1 the above requires some qualification4 ,in many cases the chemical composition of a mineral varies by a well-defined series of atomic replacements1 and we cannot feel called upon to establish a new species for every step away from the rigid type4 ,sodium thus replaces potassium to some extent in orthoclase felspar4 ,the crystalline form1 again1 may not be specifically characteristic1 as1 for instance1 in the members of the garnet series1 which crystallise in the cubic system4 ,the homogeneity of molecular structure throughout the individual may be regarded as the most essential feature of what we style a mineral species2 that is to say1 the molecules contain the same elements in the same proportions1 and are arranged on the same physical plan4 ,a rock1 on the other hand1 is a mere aggregate of mineral particles1 or of molecules that1 under proper conditions1 would group themselves to form mineral species4 ,it may consist entirely of granules or crystals of one species2 but the structures in these have no common orientation1 as they would have in a single large continuous crystal4 ,the rock itself has no crystalline form1 and any structures that simulate such forms will be found on measurement to have none of the regularity that characterises genuine crystals4 ,a rock1 moreover1 formed of several mineral species in association will by no means possess a constant chemical composition1 and the variations from point to point form a feature of especial interest in the study of igneous masses1 of sediments deposited on a shore1 or of alluvium in a valley stretching far between the hills4 ,in the pages that follow we hope1 then1 to bear in mind the relations of rocks to the earth and to ourselves4 ,like the ancient ,romans1 we build our cities with huge blocks and slabs brought from crystalline masses oversea4 ,we now tunnel1 for our commercial highways1 through the complex cores of mountain-chains4 ,everywhere rocks are our foundations1 throughout our travels or in our settled homes4 ,they rise as obstacles against us1 or they spread before us fields of fertile soil4 ,some knowledge of them is part of the general body of culture that makes us1 in the best sense1 citizens of the world4 ,,list ,,of ,,the ,,common ,,minerals ,,that ,,form ,,rocks ,actinolite4 ,see ,amphiboles4 ,albite4 ,see ,felspars4 ,amphiboles4 ,a series of silicates with the general formula ,r,si,o#c1 where ,r is magnesium1 iron or calcium2 in many1 such as the common species ,hornblende1 molecules occur in addition in which aluminium and triad iron are introduced4 ,hornblende thus consists of m 7,mg1 ,fe1 ,ca7 ,si,o#c4 n 7,mg1 ,fe7 7,al1 ,fe7#b ,si,o#f4 ,actinolite is a non-aluminous amphibole occurring in needle-like prisms4 ,the amphiboles crystallise in prisms having angles of about #ef and #abd4 ,see ,pyroxenes4 ,anatase4 ,see ,rutile4 ,andalusite4 ,aluminium silicate1 ,al#b,si,o#e1 crystallising in the rhombic system4 ,sillimanite consists also of ,al#b,si,o#e and is rhombic1 but crystallises with different fundamental angles4 ,anorthite4 ,see ,felspars4 ,apatite4 ,calcium phosphate1 with fluorine1 or sometimes chlorine1 7,ca,f7,ca#d7,,po#d7c #c;,ca#c7,,po#d7b4 ,ca,f#b4 ,aragonite4 ,calcium carbonate1 ,ca,c,o#c1 crystallising in the rhombic system1 with a specific gravity of #bic4 ,see ,calcite4 ,augite4 ,see ,pyroxenes4 ,biotite4 ,see ,micas4 ,calcite4 ,calcium carbonate1 ,ca,c,o#c1 crystallising in the trigonal system1 with a specific gravity of #bgb4 ,see ,aragonite4 ,chalcedony4 ,crystalline silica1 ,si,o#b1 in fibrous and often mammillated forms4 ,flint or ,chert is a concretionary form1 in which some interstitial opal may be present4 ,chert4 ,see ,chalcedony4 ,chlorites4 ,hydrous aluminium magnesium iron silicates1 resembling green micas1 but softer and with non-elastic plates4 ,chromite4 ,iron chromium oxide1 ,fe,cr#b,o#d4 ,magnesium may replace part of the dyad iron1 and aluminium and triad iron some of the chromium4 ,diallage4 ,an altered augite with a shimmery submetallic lustre4 ,diopside4 ,see ,pyroxenes4 ,dolomite4 ,magnesium calcium carbonate1 ,mg,ca7,,co#c7b4 ,enstatite4 ,see ,pyroxenes4 ,epidote4 ,calcium aluminium iron silicate1 ,ca#b7;,al,o,h77,al1 ,fe7#b7,si,o#d7c4 ,felspars4 ,a series of silicates of aluminium with potassium or sodium or calcium1 or all of these4 ,orthoclase1 ,k,al,si#c,o#h1 and the corresponding sodium form1 ,albite1 ,na,al,si#c,o#h1 lie at one end of the series1 and the calcium felspar ,anorthite1 ,ca,al#b7,si,o#d7b1 at the other4 ,while ,orthoclase crystallises in the monoclinic system1 a triclinic form1 ,microcline1 with the same composition1 is also common4 ,all the other felspars are triclinic1 and1 with microcline1 are often styled plagioclases4 ,the principal felspars between ,albite and ,anorthite are ,oligoclase1 the soda-lime felspar1 and ,labradorite1 the lime-soda felspar4 ,flint4 ,see ,chalcedony4 ,garnets4 ,a series of silicates with the general composition of ,r#c,r#b7,si,o#c7d1 ,r being ,ca1 ,fe1 or ,mn1 and ,r being ,al or ,fe4 ,the common red garnet in mica-schists is ,almandine1 ,fe#c;,al#b7,si,o#c7d1 while that in altered limestones is ,grossularite1 ,ca#c;,al#b7,si,o#c7d4 ,glauconite4 ,a hydrous iron potassium silicate1 with some aluminium1 magnesium1 and calcium1 formed in marine deposits4 ,gypsum4 ,hydrous calcium sulphate1 ,ca,s,o#d #b ,h#b,o4 ,hornblende4 ,see ,amphiboles4 ,hypersthene4 ,see ,pyroxenes4 ,ilmenite4 ,titanium iron oxide1 m ,fe,ti,o#c n ,fe#b,o#c4 ,iron ,pyrites4 ,iron disulphide1 ,fe,s#b4 ,a cubic species1 ,pyrite1 and a less common rhombic species1 ,marcasite1 occur4 ,kaolin4 ,hydrous aluminium silicate1 ,h#d;,al#b,si#b,o#i4 ,kyanite4 ,aluminium silicate1 ,al#b,si,o#e1 crystallised in the triclinic system4 ,see ,andalusite4 ,labradorite4 ,see ,felspars4 ,leucite4 ,potassium aluminium silicate1 ,k,al7,si,o#c7b4 ,limonite4 ,hydrous iron oxide4 ,h#f;,fe#d,o#i4 ,magnetite4 ,magnetic iron oxide1 ,fe#c,o#d4 ,marcasite4 ,see ,iron ,pyrites4 ,micas4 ,a series of aluminium silicates1 with potassium1 magnesium1 or iron1 or all of these4 ,lithium and sodium sometimes occur4 ,the two marked types are ,muscovite1 rich in aluminium and potassium1 the common alkali mica1 ,h#b,k,al#c7,si,o#d7c1 with a silvery aspect1 and ,biotite1 the common dark ferromagnesian mica1 7,h1 ,k7#b7,mg1 ,fe7#b7;,al1 ,fe7#b7,si,o#d7c4 ,microcline4 ,see ,felspars4 ,muscovite4 ,see ,micas4 ,nepheline4 ,sodium aluminium silicate1 with some potassium1 the pure sodium type being ,na,al,si,o#d2 the types with potassium contain slightly more silica4 ,oligoclase4 ,see ,felspars4 ,olivine4 ,magnesium iron silicate1 7,mg1 ,fe7#b,si,o#d4 ,opal4 ,uncrystallised silica1 ,si,o#b1 with some water4 ,orthoclase4 ,see ,felspars4 ,pyrite4 ,see ,iron ,pyrites4 ,pyroxenes4 ,a series of silicates corresponding in composition to the ,amphiboles1 but crystallising in prisms which have angles of about #hg and #ic4 ,on the whole1 the pyroxenes are richer in calcium than the amphiboles4 ,the formula of ,wollastonite is ,ca,si,o#c4 ,diopside consists of ,ca7,mg1 ,fe77,si,o#c7b4 ,augite1 the commonest form1 is aluminous1 corresponding to ,hornblende among the amphiboles2 but the change from ,augite into ,hornblende1 which often occurs1 may imply a loss of calcium4 ,enstatite and ,hypersthene are species crystallising in the rhombic system2 the former consists of ,mg,si,o#c1 while in ,hypersthene iron replaces some of the magnesium4 ,quartz4 ,silica1 ,si,o#b1 crystallised in the trigonal system4 ,rock-,salt4 ,sodium chloride1 ,na,cl4 ,rutile4 ,titanium dioxide1 ,ti,o#b1 crystallised in the tetragonal system4 ,anatase has the same composition1 and is tetragonal1 but has different fundamental angles4 ,serpentine4 ,hydrous magnesium iron silicate1 ,h#d7,mg1 ,fe7#c,si#b,o#i4 ,siderite4 ,iron carbonate1 ,fe,c,o#c4 ,sillimanite4 ,see ,andalusite4 ,talc4 ,hydrous magnesium silicate1 ,h#b,mg#c7,si,o#c7d4 ,tourmaline4 ,a borosilicate of aluminium with various other elements1 ,r#i;,al#c7;,,boh7#b,si#d,o#ai4 ,r represents ,h1 ,na1 ,al1 ,mg1 ,fe4 ,tridymite4 ,silica1 ,si,o#b1 crystallised in doubly refracting six-sided plates4 ,its specific gravity is #bc1 that of ,quartz being #bfe4 ,wollastonite4 ,see ,pyroxenes4 ,zeolites4 ,a series of hydrous aluminium silicates1 with potassium1 sodium1 calcium1 and sometimes barium4 ,zircon4 ,zirconium silicate1 ,zr,si,o#d4 ,,chapter ,,ii ,,the ,,limestones ,,introduction ,the term ,limestone covers1 by common consent1 rocks consisting mainly of calcium carbonate4 ,dolomite 7properly ,dolomite-rock71 in which half or nearly half the molecules consist of magnesium carbonate1 is1 however1 generally included4 ,the convenience of limestones as building materials has given them a world-wide interest4 ,their stratified and jointed structure appealed to the early ,egyptian architect1 when he sought blocks for his pyramids4 ,the ease with which limestones could be carved1 combined with a reasonable resistance to decay1 gave them a pre-eminence with the designers of our rich cathedrals4 ,the ,romans found in the stained and altered varieties colour-schemes for basilicas and baths1 and their luxurious taste in limestone has been inherited by the modern builders of hotels4 ,the rock suffers1 however1 from its solubility in water containing even a mild acid4 ,in the gases dissolved by rain-water from the atmosphere1 carbon dioxide assumes a far larger proportion than that which it possesses in the air itself4 ,the surface of limestone slabs becomes in consequence pitted and corroded by every rain that falls4 ,the sulphuric acid in the air of modern coal-consuming cities is1 however1 still more deadly in its action4 ,j4 ,a4 ,howe1 in his recent work on building stones1 is of opinion that limestone is unsuitable for towns4 ,limestones may broadly be recognised by their solubility in cold dilute acids1 with brisk evolution of carbon dioxide4 ,dolomitic varieties require hot acid4 ,limestones divide themselves into types produced by chemical precipitation and those due to the accumulation of the hard parts of organisms2 but in many of the latter types chemical precipitation also plays a part4 ,organic action1 moreover1 frequently promotes the deposition of the chemical types4 ,detrital limestones1 that is1 limestones formed from the debris of older ones1 are comparatively unimportant4 ,they occur in certain zones of the ,chalk and of the ,carboniferous ,limestone in our islands1 and record the breaking up in shallow water of beds that had already become consolidated4 ,the ,miocene ,nagelfluh conglomerates of the north side of the ,swiss ,alps are often formed of pebbles of the far older ,mesozoic limestones4 ,similar conglomerates1 cemented by calcium carbonate1 are now being formed in the river-beds of the limestone karstland of ,hercegovina4 ,limestone1 however1 as a rule goes to pieces before the buffetings sustained by mixed rocks on a shore4 ,even if it survives for a time in gravels1 percolating waters ultimately dissolve it1 and only a porous skeleton1 formed of its impurities1 remains4 ,,limestones ,,deposited ,,from ,,solution ,though calcium carbonate is far less soluble than calcium sulphate1 large quantities are carried invisibly1 owing to the presence of carbon dioxide1 in river waters1 and thus accumulate in inland seas that have no outlet except by evaporation4 ,here ,calcareous ,tufa may be deposited as a crust upon the shores and on the growing islets1 as the water shrinks away1 and before the more soluble gypsum and rock-salt can separate out4 ,hot springs of volcanic origin1 like the ,sprudel of ,karlsbad in ,bohemia1 may deposit calcium carbonate as the water cools and is relieved from pressure4 ,at ,karlsbad1 little grains of granite1 or of the minerals of granite1 serve as centres1 and encrusting layers are formed round them1 until pea-like bodies are produced4 ,these become cemented together1 giving rise to the well-known freshwater pisolitic limestone or roestone4 ,on the shores of the ,great ,salt ,lake of ,utah1 calcareous tufa occurs also in the form of grains resembling little eggs4 ,these are the oolitic grains that were first known as constituents of fossil limestones4 ,the calcium carbonate of oolitic grains at ,karlsbad1 from the ,great ,salt ,lake1 and from the sea1 is deposited in a form that gives the reaction of aragonite when boiled in cobalt nitrate4 ,a4 ,lacroix1 however1 finds that the material at ,karlsbad has a specific gravity lower even than that of calcite1 and that its double refraction is also distinctly weaker4 ,he has called this form of calcium carbonate ktypeite4 ,travertine is a tufa laid down on twigs and other vegetation1 where springs emerge laden with calcium carbonate4 ,in a massive form1 it builds tufa-basins1 as in the ,mammoth ,hot ,springs of the ,yellowstone ,park4 ,both here and at ,karlsbad1 it appears that vegetation of humble type1 multiplying under warm conditions1 materially assists the deposit by withdrawing carbon dioxide from the water4 ,the unstable calcium bicarbonate is thus converted into the carbonate1 which is thrown down as a quickly increasing crust4 ,among the limestone regions of the ,dinaric ,alps1 calcareous tufas or travertines1 laid down by ordinary streams1 form massive beds that tend to choke the hollows of the hills4 ,the basin of ,jajce in ,bosnia is thus partially filled up1 and the town is built on materials brought in solution from the mountains4 ,the modern waters are still adding to this deposit1 and ,fr4 ,katzer#d has pointed out that the falls of the ,pliva are prevented from cutting their way down to the level of the ,vrbas ravine1 into which they plunge1 by the mass of tufa which they build up in their own course4 ,another type of limestone deposited from solution is of considerable interest in arid lands1 or lands with only a seasonal rainfall4 ,where evaporation goes on steadily at the surface1 while water is brought up by capillary action from below1 calcium carbonate may form a cement to the soil1 or to the crumbling rock near the surface1 and a solid calc-tufa may arise by continued transference of matter in solution from lower levels4 ,in the ,cape of ,good ,hope such formations are conspicuous#e4 ,in a careful series of experiments1 ,g4 ,linck#f showed in #aijc that sea-water at #ag ,c4 can only hold #jaia per cent4 of calcium carbonate in solution4 ,though this quantity is not realised in the open ocean1 yet near shores rivers may bring down an excess4 ,the ,thames1 though flowing for a long distance over a limestone area1 contains only #jaaf per cent4 of calcium carbonate2 but springs traversing limestone often carry #jc per cent41 or ten times as much as that found in ordinary seas4 ,hence a precipitation of calcium carbonate from the bicarbonate state may take place not far from land4 ,the mineral deposited is calcite in temperate climates and aragonite under warm tropical conditions4 ,that such a precipitation actually occurs is proved by the massive grey limestones1 containing modern shells1 which have been recorded for our islands from the sea-floor off the ,isle of ,man and off the coast of ,mayo4 ,in the case of the ,irish ,channel1 the excess of calcium carbonate may be supplied by springs rising through the glacial gravels1 which contain abundant pebbles of limestone4 ,ammonium carbonate1 again1 derived from the decay of organisms1 or sodium carbonate1 will precipitate calcium carbonate as aragonite from the calcium sulphate and chloride1 but not from the calcium bicarbonate1 of salt water4 ,films of aragonite are at present accumulating by this process on the floor of the ,black ,sea1 and marine oolitic grains1 also consisting of aragonite1 are produced by the same reaction4 ,in the case of oolitic grains1 deposition is no doubt helped by evaporation1 since they seem to arise in shallow waters4 ,the ,oolitic ,limestones that have proved so admirable as building stones1 whether from the quarries of ,caen or ,portland1 are cemented representatives of the loose deposits formed in modern tropical seas4 ,de la ,beche long ago compared their grains with those from ,west ,indian coral-reefs4 ,these small egg-like bodies develop round fragments of foraminiferal and other shells1 round the ossicles of echinoderms1 and round broken bits of coral4 ,at first they have the general form of the nucleus2 but1 as they are rolled by the waves during their growth1 they become more and more spheroidal as they enlarge4 ,boring alg make tubular passages in them1 and these have led to the view that alg of thread-like form actually originate oolitic structure4 ,doelter1 ,linck1 and others conclude1 with much reason1 that the mode of deposition is inorganic4 ,when the grains are unusually large1 they are often flattened and irregular1 as in the marine ,pisolites or ,pea-grits4 ,for building purposes1 the fine-grained oolites without large fossils are much sought after1 since they can be trimmed equally in any desired direction4 ,before leaving the question of the inorganic deposition of limestone1 we may note that ,r4 ,a4 ,daly#g has suggested that the pre-,cambrian and early ,cambrian limestones were entirely products of chemical precipitation4 ,he believes that the continental areas were at first relatively small1 and that the abundance of decaying soft-bodied organisms on the sea-floor led to a continuous precipitation of such calcium carbonate as was available4 ,hence the ocean was limeless1 and it was only when continental land became more extended that a sufficient quantity of lime salts was brought in by rivers to counterbalance that thrown down by ammonium carbonate and sodium carbonate on the sea-floor4 ,daly urges that1 on this account1 the earlier organisms could not form calcareous shells or skeletons1 and he also believes that pre-,cambrian and ,cambrian limestones1 even when unaltered1 show no signs of having originated from fragmental organic remains4 ,linck's researches 7p4 #ag7 show that limestones thus precipitated must have originally consisted of aragonite4 ,,limestones ,,formed ,,of ,,organic ,,remains ,these limestones present an immense variety1 according to the nature of the originating organisms1 and the amount of foreign material brought down into the water where they accumulated4 ,the calcareous remains of ,chara may form a white deposit on the floors of freshwater lakes4 ,the part played by calcareous alg in the formation of marine limestones has long been recognised2 but the detailed exploration in #aijd of the atoll of ,funafuti in the ,pacific showed that ,halimeda may be responsible for a considerable portion of an ordinary coral-reef4 ,lithothamnium occurs in immense quantities1 associated with molluscan remains1 near many shores1 and forms a large part of the material of the raised beaches in ,spitsbergen4 ,animal1 not vegetable1 activity1 however1 is responsible for the majority of our limestones1 and the humbler organisms1 by reason of their abundance1 play a prominent part in rock-formation4 ,analogies between the ,globigerina-ooze of deep waters and the groundwork of the soft white limestone known as ,chalk have been freely pointed out4 ,early in the nineteenth century1 ,ehrenberg1 in a series of researches with the microscope1 proved the organic origin of the compact ground of marine limestones4 ,the occurrence of foraminifera from the shore outwards to truly oceanic waters provides a fine-grained calcareous material which forms deposits at very various depths4 ,the milioline types1 often with a surface like that of glazed porcelain1 are common in the sandy beds formed near a coast4 ,few rocks are more fascinating under the microscope than those in which such types are seen in section1 associated with detrital grains of quartz1 washed down from the land1 and perhaps with bright green grains of the marine mineral1 glauconite4 ,in ,ireland white chalks occur1 speckled throughout with glauconite1 which looks dark in the rock-mass1 but which reveals its green tint when streaked out by the hammer4 ,when formed still farther from land1 pure chalk arises from the consolidation of foraminiferal ooze1 and the probable depth in which it accumulated must be judged from the nature of the associated organisms4 ,a white limestone may1 however1 arise in a comparatively shallow sea1 where the rivers bring down little solid matter from the land4 ,a coast formed of pure limestone1 with clear streams flowing from a land of similar rock behind1 may allow of the development of pure limestone on its shores4 ,it is generally agreed that the ,upper ,chalk of the ,british ,isles and of northern ,france was laid down in water one thousand fathoms or more in depth2 yet the corresponding white limestone of northern ,ireland in places follows rapidly on conglomeratic and glauconitic deposits1 and seems to owe its purity to the comparative absence of rain and rivers on the highland of crystalline rocks which stretched westward from its shore4 ,there are two epochs of the earth's history in which foraminifera were remarkable for their size as well as their abundance4 ,the first gave us the grey ,fusulina limestone of ,upper ,carboniferous times1 when this spindle-shaped shell spread freely from the ,united ,states through the arctic regions to the east of ,asia4 ,the second gave us1 in the ,eocene period1 the great beds formed of ,nummulites and ,orbitoides1 which we meet with in ,europe on the ,lake of ,thun1 but which are far more important in ,lower ,egypt4 ,the disc-like forms of the nummulites in the white limestone of the ,pyramids are familiar to hundreds of travellers1 and forms are recorded up to four and a half inches across4 ,the foraminiferal origin of many compact limestones can often be appreciated on smooth surfaces with a pocket-lens4 ,the older examples have commonly become stained and darkened1 and crystallisation of calcite throughout the ground has in part destroyed the original organic structures4 ,this tendency to crystallise affects even the larger fossils1 and brachiopods and molluscs have sometimes disappeared from our ,carboniferous limestones1 without the intervention of metamorphic heat or pressure4 ,in most limestones older than the ,eocene period1 the shells and other fossils1 such as corals1 that were originally formed of aragonite have passed into the calcite state1 without the destruction of their characteristic shapes4 ,shells1 however1 have been found still preserved as aragonite in beds as old as the ,jurassic period#h4 ,the lamellibranchs1 the ordinary bivalves1 came into prominence as limestone-builders with the ,carboniferous period1 and are now rivalled by the univalve gastropods1 which displayed no widespread activity until ,eocene times4 ,the most massive existing shell1 however1 is a lamellibranch1 the giant ,tridacna of ,australian seas1 a single valve of which may weigh #bej lbs4 ,the cephalopods1 though lying far nearer to the crown of molluscan development1 became important from the ,silurian ,orthoceras onwards1 and nautiloids of various forms are common fossils in the ,carboniferous limestone4 ,their large size attracts attention from our present point of view4 ,the cephalopods1 however1 swell the bulk of many limestones1 not by the thickness of their shells1 but through their chambered character1 which has prevented complete infilling of the shell1 and which thus allows of cavities in the mass4 ,this is notably the case with the ammonites1 which contribute so largely to ,jurassic limestones4 ,crystalline calcite has often been deposited by infiltration on the septa and on the inner layer of the shell1 thus reducing the hollow spaces4 ,the massive calcite guards of the belemnites form a considerable part of many limestones4 ,even freshwater lakes possess molluscan deposits1 producing a white limestone of their own4 ,where streams flow over pure pre-existing limestone1 there is no alluvial mud to choke the basins4 ,in the hard lake-waters1 gastropods such as ,limna and ,planorbis1 and a few bivalves1 can then flourish freely1 and a shell-marl accumulates at the bottom1 unmixed with sediment4 ,limestone of this type is conspicuous in hollows in the ,dinaric ,alps1 which were once occupied by lakes1 and is often found beneath peat in the limestone lowland of central ,ireland4 ,in older days1 two groups of organisms1 now relatively unimportant1 had a powerful place4 ,the brachiopods1 including in early ,palozoic times an interesting series of thin shells largely composed of calcium phosphate1 were for long the predominant shell-bearing organisms4 ,the stout ,spiriferid and the well-known ,productus giganteus of the ,carboniferous period illustrate their dominance4 ,the group became much restricted in variety in ,jurassic times2 but even then ,terebratula and ,rhynchonella occurred so abundantly that they now fall out of many rock-faces like pebbles from a loose conglomerate4 ,the sea-lilies have similarly lost their place as limestone-builders1 though their ossicles1 notably from their stems1 furnish crinoidal or encrinital masses from ,silurian to ,carboniferous times4 ,the broken portions of their stems1 resembling tubes of tobacco-pipes1 are conspicuous when they are weathered out on rock-surfaces or revealed in polished slabs of marble4 ,the fact that each joint or ossicle1 as is the universal case in the echinodermata1 consists of a single crystal of calcite causes the fragments to break with the characteristic cleavage of that mineral4 ,the smooth glancing surfaces thus seen on fractured specimens readily call attention to them in a rock4 ,those humble colonial organisms1 the compound corals1 have so special a place as limestone-formers that they have been reserved for more detailed treatment4 ,the accumulation of their skeletons1 and the fact that they may form large continuous masses by their very mode of growth1 promotes the formation of solid rock at an unusual rate4 ,von ,richthofen long ago pointed out how foraminifera and other drifted material became caught in the interstices of coral1 producing even a stratified structure in the hollows of a reef2 and subsequent research has shown the composite character of reefs in various portions of the tropic seas4 ,calcareous alg as already remarked1 and the massive and often encrusting skeletons of hydrozoa1 such as ,millepora1 are freely associated with the products of true corals4 ,charles ,darwin1 in his famous theory of the formation of atolls and barrier-reefs1 showed how1 in a subsiding area1 corals might keep pace with the downward movement4 ,hence reefs might arise of great vertical thickness1 although the polypes themselves could flourish only in the upper twenty fathoms or so of water4 ,this conclusion1 which appears strictly logical1 has met with much opposition from ,karl ,semper1 ,alexander ,agassiz1 and ,sir ,john ,murray4 ,murray in particular urges the importance of banks of calcareous organisms in building up platforms on which corals may ultimately dwell4 ,the extension of reefs outward into deep water has been attributed to the rolling down of wave-worn coral debris over submarine mountain-slopes4 ,from this point of view1 an apparently thick atoll may be formed as a comparatively thin mass of limestone at the summit of a volcanic cone that fails to reach the sea-level4 ,the opponents of the view that thick coral-limestones are formed at the present day in the ,pacific have been unwilling to accept the results even of the deep boring in the atoll of ,funafuti#i1 which penetrated materials like those of the superficial layers of the reef to a depth of #aaad feet4 ,they have also refused to see in the huge dolomitic rocks of ,tyrol the remains of ,triassic reefs four thousand feet in thickness4 ,none the less1 most geologists regard the ,funafuti boring as a strong support for ,darwin's contention4 ,whatever may be proved as to the origin of this or that atoll at the present day1 it is clear that the possibility of subsidence leads us to expect considerable coral-limestones among our ancient rocks4 ,the same problem arises wherever we have a rich molluscan fauna continuously represented in two or three thousand feet of limestone1 or where we find shore-deposits of any kind accumulated to an unusual thickness4 ,darwin1 at the end of the fifth chapter of his work on ,the structure and distribution of ,coral-,reefs1 gives a vivid account of the features that would appear in a section of an atoll that has grown large through subsidence of its inorganic floor1 and he emphasises the occurrence of conglomerates of broken coral-rock on the outer zone4 ,the stratification of material by wave-action in this zone1 and the horizontal deposition of finer material in the lagoon1 would give to the dissected mass a general sedimentary aspect4 ,darwin concluded that the ring of solid coral1 the true reef1 might be denuded away during an epoch of elevation1 and that only stratified portions might remain4 ,he does not seem to have discussed the contemporaneous deposition of pelagic material from foraminiferal and other sources against the outer surface of the reef whereby an interlocking of two facies of limestone might arise4 ,these features1 together with those predicted by ,darwin1 have been recognised by von ,richthofen and ,mojsisovics in the ,tyrol dolomites1 and have afforded ,austrian geologists good evidence that large parts of these limestones originated as coral-reefs4 ,faulting1 however1 has undoubtedly taken place in this region1 producing here and there a subsidence of the limestone blocks among the surrounding more normal sediments4 ,rothpletz1 ,ogilvie ,gordon#aj1 and other critics of von ,richthofen's view have seen in this faulting the cause of the abrupt change from a facies of massive dolomite to one of normal sedimentation on the same horizontal level4 ,they have also urged that shell-banks may accumulate locally so as to simulate reefs by their contrast with their surroundings1 while the change to dolomite has obliterated their original features 7see p4 #cj74 ,it cannot be denied1 however1 that coral-reefs and their associated detrital deposits must exercise a very important influence in the formation of solid limestone4 ,even small knots and local groups of compound corals are seen in ordinary limestones to serve as a mesh in which other organic remains have become entrapped4 ,the ease with which the aragonite of their skeletons becomes silicified causes them often to stand out on weathered surfaces with all the delicacy of structure displayed upon a modern reef4 ,where limestones and shales are associated together1 a knoll structure may be found1 the limestone occurring in masses of a somewhat hemispherical form1 with the shales fitted against and round them4 ,in some cases this may be due to the local distribution of patches of growing coral on the old sea-floor2 but in other cases the structure has arisen from compression and brecciation of the strata1 the original beds of limestone becoming broken up and the more yielding beds flowing round them4 ,this structure is well seen on a small scale in many crush-conglomerates1 where the limestone appears as knots and eyes1 resembling pebbles4 ,yet near at hand the true bedding may be traced1 bands of limestone alternating with shale1 and a few cross-joints indicating the possibility of a separation of the limestone into blocks4 ,these blocks become rounded in the general rock-flow2 but ,gardiner and ,reynolds#aa suggest solution by infiltering water as an explanation of certain remarkable examples studied by them4 ,,altered ,,forms ,,of ,,massive ,,limestone ,a certain amount of magnesium carbonate is present in the skeletons of some marine organisms4 ,this has been shown both by ,forchammer and ,walther#iaa4 ,a foraminifer1 ,nubecularia novorossica1 has been found with #bf per cent4 of magnesium carbonate1 and a serpula with #gfd per cent42 alcyonarian corals contain up to #icb per cent41 while calcareous alg1 such as ,lithothamnium and ,halimeda1 contain about #ab per cent4#ab4 ,the magnesium salt is not1 however1 here combined with calcium carbonate to form the mineral dolomite2 none the less it is clear that such organisms introduce magnesium in appreciable quantities into the constitution of marine limestones4 ,marine limestones are very commonly dolomitised4 ,dolomite1 the joint carbonate1 ,ca,mg7,,co#c7b1 contains #edce per cent4 of calcium carbonate and #defe per cent4 of magnesium carbonate1 or carbon dioxide #dgh1 lime #cjd1 and magnesia #bah4 ,its specific gravity is #bhe4 ,the occurrence of dolomite in intimate association with calcite has been proved by ,e4 ,w4 ,skeats#ac in the case of modern coral-reefs1 and the secondary deposition of the mineral has been made clear4 ,the skeletons of the corals themselves may now consist of dolomite1 while calcite has crystallised in their interstices1 or remains as part of the original infilling of mud4 ,the presence of dolomite in reefs has1 of course1 long been known1 having been observed by ,j4 ,d4 ,dana in #ahdi1 and it has been realised that1 by prolonged alteration1 masses of ,dolomite ,rock become built up#ad4 ,commonly1 the process produces a ,dolomitic ,limestone1 in which calcium carbonate is still in excess of the #ed per cent4 which is present in the mineral dolomite4 ,the alteration of the original limestone is1 however1 sufficiently profound4 ,the ready crystallisation of dolomite as rhombohedra destroys the organic structure1 and traces of corals or molluscan shells disappear from great thicknesses of rock4 ,it is uncertain whether the process of dolomitisation proceeds most rapidly in the evaporating waters of the lagoons1 or1 as ,pfaff believes1 at considerable depths1 where the pressure may reach #ajj atmospheres4 ,magnesium carbonate1 as we shall note later1 may be removed from dolomite in solution under pressure at a greater rate than calcium carbonate4 ,if this occurs in sea-water1 it would seem to militate against the production of dolomite in the lower levels of a reef4 ,the magnesium required for dolomitisation is derived from the magnesium sulphate and chloride of sea-water1 calcium being removed during the change4 ,c4 ,klement in particular urges that a concentrated solution of sodium chloride at #fj ,c4 assists the process in the case of magnesium sulphate4 ,aragonite1 the material of coral skeletons and of most molluscan shells1 is more susceptible than calcite4 ,the temperature of ,klement's experiments may be realised in lagoons or between tide-marks1 and ,doelter suggests that the element of time in nature may allow the reaction to take place at lower temperatures4 ,the intimate structure of modern dolomitic limestone1 as exhibited in coral-reefs1 satisfies us that many older or fossil dolomites were formed from marine calcareous deposits while these were still accumulating4 ,in other cases we must admit that the dolomite has developed in the neighbourhood of joints after the consolidation of the rock4 ,the view that dolomitisation results from the mere removal of calcium1 the magnesium originally present in organic skeletons becoming thus more concentrated1 is not borne out by recent observations4 ,skeats#ae has carefully compared the dolomite-rocks of ,tyrol with the materials of recent coral-reefs4 ,in both there is a striking absence of detritus of inorganic origin1 and his work goes far to show that the much-discussed ,alpine dolomites were formed under conditions which occur in the neighbourhood of existing reefs4 ,this1 however1 does not solve the question as to whether we are dealing in ,tyrol with fossil coral-reefs1 or with the calcareous type of ordinary marine sediments1 which might undergo the same kind of alteration4 ,while ,skeats finds in two dolomites from recent reefs #dc per cent4 of magnesium carbonate1 the substitution seems usually to terminate when #dj per cent4 has been introduced4 ,in ,tyrol1 however1 the process has gone so far as to give rise to true dolomites1 with #defe of magnesium carbonate4 ,the dolomites of the ,jurassic series in north ,bavaria are massive rocks almost devoid of fossils1 traversed by shrinkage cracks1 and associated with richly fossiliferous stratified limestones4 ,the relations of these two types of rock are those of coral-reefs to the bedded deposits on their flanks1 and the dolomite seems to merge horizontally into the stratified series4 ,as in ,tyrol1 fossils and corals are rare in the bosses of dolomite1 but the structural evidence is strongly in favour of their having originated as steeply sided reefs4 ,the dolomitic facies of the ,carboniferous limestone in our islands is an example of the second type of origin4 ,the dolomite here frequently occurs in irregular veins and patches4 ,the introduction of iron carbonate with the magnesium salt stains the dolomite brown on exposure to oxidation1 and its limits are thus clearly seen in the general blue-grey mass4 ,the dolomitisation has evidently proceeded from joint-surfaces inwards4 ,it is often sufficiently thorough to obliterate all traces of fossils1 and the shrinkage accompanying the chemical change has produced numerous cavities1 in which calcite has subsequently crystallised4 ,an expansion takes place when aragonite is altered into dolomite1 unless more of the calcium carbonate is removed than is necessary to give place to the magnesium carbonate introduced4 ,in the change from calcite1 with a density of #bgb1 to dolomite1 with a density of #bhe1 there is1 on the other hand1 a shrinkage of #def per cent4 ,where the alteration1 then1 takes place while the aragonite organisms still remain as aragonite1 and not as calcite1 an expansion rather than a contraction should occur in the substance of a reef2 but when an old limestone1 in which all the calcium carbonate is present as calcite1 becomes dolomitised1 a considerable shrinkage will occur1 and rifts and hollows may remain obvious4 ,very few dolomites1 except those found in association with rock-salt and other products of the evaporation of lagoons1 can now be attributed to direct chemical deposition from the sea4 ,daly#g has argued that the first ,palozoic and the pre-,cambrian dolomites were formed by precipitation1 since the calcium salts in those early days were completely removed from the sea-water4 ,ammonium carbonate1 though effective in precipitating the calcium salts1 does not act on those of magnesium until the calcium salts have been brought down4 ,but1 under the conditions postulated for the river-waters that reached the sea from the earliest continental lands1 conditions involving the presence of only small quantities of salts of calcium1 the decay of organisms on the sea-floor might lead to a deposition of all the magnesium salts1 following on those of calcium1 both coming down in the form of carbonates4 ,the experimental work of ,pfaff#af should be considered in connexion with ,daly's suggestions1 since means are there indicated whereby basic magnesium carbonate1 precipitated from sea-water1 may associate itself with calcium carbonate to form dolomite2 shallow-water conditions1 with concentration by evaporation1 are required4 ,daly compares analyses of river-waters now running over pre-,cambrian rocks with analyses of pre-,cambrian limestones1 and the ratio of the carbonates of magnesium and calcium is shown to be the same in both series4 ,from what we have said1 it now seems probable that the great majority of dolomitic limestones owe their magnesium to substitution from without4 ,direct precipitation of dolomite has1 however1 been invoked to account for several cases of ,permian age1 such as the ,magnesian ,limestone of the county of ,durham4 ,near ,sunderland1 this rock is greatly modified1 containing ball-like and other concretions1 associated with frequent cavities4 ,traces of the original bedding remain1 running through the concretions1 and marine fossils are abundant4 ,conybeare and ,phillips1 so far back as #ahbb1 stated that the nodules were devoid of magnesia1 though formed in a magnesian rock4 ,in spite of this1 these objects long appeared as dolomite in collections4 ,e4 ,j4 ,garwood#ag showed conclusively that they resulted from the concentration of calcium carbonate in a concretionary form4 ,the process whereby a dolomite may thus revert towards the ordinary limestone condition1 with removal of magnesium in most cases1 has been styled dedolomitisation4 ,water containing calcium sulphate after passing through a dolomite is found to carry magnesium sulphate by a chemical exchange4 ,skeats#ah1 moreover1 points out that1 under a pressure of five atmospheres the magnesium carbonate of dolomite becomes more soluble than the calcium carbonate in fresh water containing carbon dioxide4 ,the ordinary relations are thus reversed under pressure1 and a cause of dedolomitisation may be indicated4 ,under the influence of contact-action from igneous rocks1 dolomite may separate into calcium carbonate1 magnesium oxide1 and carbon dioxide4 ,the magnesium oxide takes up water and yields the flaky colourless mineral brucite4 ,where silica is present1 either as an impurity in the dolomite1 or introduced from an invading siliceous magma1 magnesium and calcium silicates may be built up#ai4 ,olivine thus arises1 and1 on becoming hydrated and passing into serpentine1 stains the rock in various shades of green4 ,the calcium carbonate crystallises as a ground of granular calcite1 and the whole mass becomes a handsome ,ophicalcite1 or serpentinous marble4 ,the famous rock of ,connemara1 used in polished slabs1 has arisen through contact with intrusive diorite4 ,dolomitic limestones are liable to decay rapidly in towns1 owing to the formation of magnesium sulphate1 which1 as shown above1 is even more soluble in water than is the accompanying calcium sulphate4 ,in the country1 the crystals of dolomite resist ordinary weathering by the carbon dioxide of the rain-water better than those of calcite2 and the rock thus becomes loosened through the loss of one constituent1 and crumbles into a dolomite sand#bj4 ,compact dolomites1 however1 have furnished some excellent building-stones for country use1 since here the more resisting mineral forms the bulk of the rock4 ,the ,phosphatic ,limestones are commercially even more important4 ,tricalcium orthophosphate1 derived1 perhaps1 in the first instance from the decay of bones of fishes and the excreta known as coprolites1 tends to become aggregated in certain limestones1 as in the chalk of ,mons in ,belgium and of ,taplow in ,buckinghamshire4 ,the phosphate replaces foraminiferal and other shells1 and frequently forms internal casts of fossils4 ,in the latter case1 it has replaced the calcareous mud that first occupied the shells4 ,the observations of the ,challenger expedition show that concretionary calcium phosphate is forming among the calcareous and glauconitic oozes of existing oceans1 nodular masses collecting1 in which foraminiferal shells are united and even replaced by calcium phosphate4 ,where deposits of guano are formed by sea-birds on surfaces of coral limestone1 as at ,christmas ,island to the south of ,java and at ,sombrero in the ,windward ,islands1 calcium phosphate becomes washed downwards and replaces part of the calcium carbonate of the rock4 ,the resulting phosphatic limestone is quarried on a commercial scale1 and the very existence of ,christmas ,island is said to be threatened by the energy of excavators4 ,the phosphorites du ,quercy1 well known to agriculturists in ,france1 are accumulations in hollows and fissures of ,jurassic limestone1 and are associated with the bones of fossil mammals4 ,but in this and in other cases there is much doubt as to whether the phosphate is derived from the bones1 or is locally concentrated1 with other impurities1 such as sand and clay1 through solution of the adjacent limestone4 ,the most common substance that replaces calcium carbonate in limestones is silica1 in the form of ,flint4 ,the nodules of this material1 white on the outside and richly black within1 mark bands of stratification in the ,cretaceous chalk1 and are among the best known materials in south-east ,england4 ,their fantastic forms have given rise to many speculations4 ,sometimes1 however1 when fractured1 they are clearly seen to include the remains of fossil sponges4 ,the sponges may be represented merely as hollow casts2 but there is abundant evidence in other cases that they belong to genera which secreted skeletons of amorphous 7non-crystalline7 silica during life4 ,the nodular flint has collected round the sponge1 while the sponge itself has often disappeared4 ,g4 ,j4 ,hinde#ba has shown how readily the spicules of siliceous sponges go into solution4 ,even at the bottom of existing seas they become rounded at the ends1 while their canals become enlarged4 ,in some fossil instances1 they are replaced by calcite4 ,w4 ,j4 ,sollas#bb1 emphasising this point1 remarks that it may be taken as an almost invariable rule that the replacement of organic silica by calcite is always accompanied by a subsequent deposition of the silica in some form or other4 ,this subsequent deposition is frequently at the expense of calcite in some other part of the rock4 ,the solid flint is a replacement of the limestone in which it occurs4 ,the pocket-lens will often show traces of sponge-spicules1 as dull little rods1 in the translucent substance of a flint4 ,but the microscope shows that the mass of the flint has the structure of the limestone in which it lies4 ,the foraminifera and other small structural features of the original rock are perfectly preserved in chalcedonic 7that is1 minutely crystalline7 silica4 ,larger fossils1 such as thick molluscan shells and the tests of sea-urchins1 may escape alteration1 while the chalk mud1 the original ooze1 with which they are infilled has become completely silicified4 ,this explains the internal moulds of fossils in brown oxidised flint that are found in gravel-pits on the surface of the ,chalk1 and also the tubular hollows1 representing stems of crinoids1 that often occur in flint from the ,carboniferous ,limestone4 ,in the latter case1 the fossil remained calcareous while the ground became silicified1 and the fossil was removed by subsequent solution4 ,where great thicknesses of strata1 as may happen in the ,carboniferous ,limestone1 have become thus silicified1 it may be presumed that siliceous skeletons were unusually abundant in the mass4 ,but1 as ,l4 ,cayeux#bc observes1 such skeletons may be in one case entirely removed1 and in another represented by massive flints2 in yet another case1 the silica may remain disseminated through the rock4 ,the irregularity of its segregation is shown by the growth of flints in branching or hook-like forms1 running from one bed to another in a limestone4 ,oolitic limestones and the skeletons of corals1 both having been originally made of aragonite1 are often replaced by flint1 forming conclusive instances1 appreciable by the naked eye1 of the secondary origin of this form of silica4 ,traces of diatoms are comparatively rare1 though they probably contributed to the silicification of the freshwater ,calcaire de la ,brie of the ,paris basin4 ,radiolaria1 however1 have now been well recognised as flint-formers1 even in dark cherts of ,silurian age4 ,radiolarian cherts have been taken as an indication that the beds in which they occur were formed in oceanic depths4 ,it is difficult to determine the stage in the history of a rock at which silicification has set in4 ,as ,a4 ,jukes-,browne#bd remarks1 solution of the silica skeletons may be accelerated by pressure1 i4e4 by the depth of water in which the bed accumulated4 ,yet1 in comparison with the calcareous shells of foraminifera1 radiolarian and diatomaceous remains are only slowly soluble1 and are found in the deepest spots reached by soundings4 ,h4 ,b4 ,guppy#be1 on the other hand1 has observed silicification of modern corals in reefs in the ,fijis1 and believes that the process went on during the elevation of the area1 when waters containing silica became concentrated1 and parts of the mass were exposed to evaporation4 ,the instability of the non-crystalline siliceous skeletons in geological time makes it probable that a rock cannot long retain them when buried among other strata in the earth4 ,it is clear that there is no support for the view1 current from the time of ,james ,hutton onwards1 that nodular flints are formed by matter in hot solutions entering pre-existing cavities in limestone rocks4 ,but there must be cases where the silicification of limestone has arisen through its penetration by hot springs4 ,the presence of tabular flint in joints of the ,chalk shows that water has imported silica along easy lines of passage from some other portion of the rock4 ,just as stems of trees become replaced by chalcedonic silica1 so may beds of limestone be converted into flint1 especially in volcanic areas4 ,a4 ,w4 ,rogers#bf records that recent limestones formed in the ,cape province by the evaporation of ascending waters have already become silicified4 ,these flinty rocks have been found in the ,kalahari ,desert and elsewhere1 though not south of the ,orange ,river2 the chemical change is probably due to the character of local water rather than to temperature4 ,yet it is remarkable how1 in the vast majority of instances1 the partial or complete silicification of a limestone may be traced to an intermediate resting stage of the silica in the form of skeletons of the vegetable diatoms or the animal sponges or radiolarians4 ,the decay of flint itself1 by the removal of part of its substance in solution1 is the cause of the white surface on specimens from the ,chalk1 and of the crumbling white residues found in certain gravels4 ,this process has been fully discussed by ,j4 ,w4 ,judd1 who believes that the material removed is silica in the opaline condition#bg4 ,,limestone ,,and ,,scenery ,limestones in the field are characterised by joints which traverse considerable thicknesses of strata1 until some shaly bed is met with1 in which earth-stresses cannot set up such continuous planes of fracture4 ,since the conditions of deposition may remain constant for a long time in open seas1 and since stratification cannot be obvious until these conditions change1 limestones may have a massive character that is exceptional among sedimentary rocks4 ,in some cases1 however1 where muddy rivers in times of flood have brought in detritus from the land1 rapid and no doubt seasonal alternations of shale and limestone may be observed4 ,the ,chalk of north-western ,europe remains typically soft1 lending itself to cliff-formation along the coast1 where landslides are frequent through undercutting from below4 ,were it not for the development of flints along stratification-planes1 it would be impossible at a distance to detect any bedded structure in the rock4 ,its representatives in eastern ,france1 in the north zone of the ,alps1 or in the central ,apennines1 are compressed into far more resisting masses1 and rear themselves as terraced crags and sheer rock-walls1 in which the structure due to vertical joints is paramount4 ,the ,english ,chalk weathers into round-backed downs1 clothed with thin grass1 and hollowed into combes by streams that have long ago run dry4 ,the soil owes hardly anything but its abundant flints to the white limestone rock on which it lies4 ,residual clays and sands derived from the breaking up of later beds allow of cultivation here and there1 and beechwoods flourish even on the crests of the high downs4 ,but water sinks freely into the ground1 and may so far saturate the mass as to appear again in wet seasons in hollows of the surface as temporary springs or bournes4 ,when deep wells are sunk and pumping is begun1 it is found that the supply varies greatly in different spots under seemingly uniform conditions4 ,even in so permeable a mass1 there are waterways where maximum flow occurs4 ,channels where water soaks in from above1 or weak places in the roofs of underground watercourses1 become marked at the surface by sinkings known as swallow-holes4 ,these increase in size with time1 and are abandoned to the growth of scrub and trees4 ,among more consolidated limestones1 as we have hinted1 the joints are effective in promoting bold rock-scenery4 ,the absorptive power of the rock1 rather than its hardness1 prevents it from being washed away4 ,water that might round the edges of escarpments and send down taluses to modify the slopes sinks into the ground and works out passages by solution4 ,on level surfaces1 the solubility of limestone in water charged with carbon dioxide from the atmosphere is apparent by the formation of pitted hollows1 with edges between them that grow sharper until they are worn through4 ,where a rain-drop first secures a resting-place1 its successors deepen the little hollow4 ,water lies in this after every shower1 working its way gently downwards4 ,in time the rock may seem bored into as if prepared for blasting2 the holes unite to form vertical grooves1 and the surface is cut deeply into fantastic forms4 ,the face of the rock1 formed by weathering on a valley-side or towards the sea1 or occurring on any mass that is being cut back and reduced by denudation1 is likely to be vertical1 or at any rate perpendicular to the bedding4 ,the form of the surfaces of the beds is perpetuated by their fairly uniform lowering through solution4 ,the result is that stratification surfaces and planes perpendicular to them control in a very marked degree the scenery of limestone lands 7,fig4 #a74 ,illustration3 ,fig4 #a4 ,surface of ,limestone ,plateau4 ,causse du ,larzac1 ,aveyron1 ,france4 ,where the beds are level1 with occasional partings of a slightly different composition1 the country will develop terraces1 like those of the ,burren in northern ,clare4 ,where they are folded1 as in the ,juras1 scarps and dip-slopes follow one another picturesquely1 the weathered edge of the bed1 the true escarpment1 being sometimes at an angle as steep as that of the dip4 ,hence a false effect of sharp peaks is produced1 when these edges are seen end on at a distance4 ,the terrace-structure may be seen in miniature forms upon a rocky shore1 where the blocks loosened from the escarpments of the successive beds are carried away by the waves4 ,frost-action is powerful in larger instances1 and sends down huge blocks upon the lower terraces4 ,a combination of shale bands and massive limestones1 especially with a dip outward from the highland1 leads to destructive landslips1 since the sloping surface of shale is lubricated by water that passes through the limestone 7see ,fig4 #i74 ,outward slips of the coast are thus common in ,antrim1 and have been extensive near ,axmouth1 two regions where chalk rests upon ,liassic clays4 ,broken ground1 then1 occurs freely under limestone scarps1 and the falling blocks often prevent the growth of trees4 ,the freshness of the rock-face above and of the talus below calls attention to spots where denudation is most active4 ,differences in the constitution of the beds are indicated by differences of the slope formed by denudation on the rocky walls4 ,the huge caons of ,arizona afford effective illustrations4 ,illustration3 ,fig4 #b4 ,ravine in ,limestone4 ,caon of the ,dourbie1 ,aveyron1 ,france4 ,these caons owe much of their character to the presence of vertically jointed limestone4 ,the small rainfall of the region has allowed the rivers to deepen their channels ahead of the wearing back of the walls4 ,yet even where valleys are widened by rain and other atmospheric agents1 those formed in limestone will maintain the character of ravines4 ,in the valley-sides of ,derbyshire1 or of the ,franconian plateau1 or of the ,arve near ,sallanches1 where the crags rise a mile or more above the stream1 we see how caon-cutting is assisted by the joints in limestone4 ,the ravine of the ,dourbie1 east of ,millau in ,aveyron1 in the romantic region of the ,causses1 is a winding gorge two thousand feet in depth 7,fig4 #b74 ,that of the ,tarn1 a little to the north1 has only recently been penetrated by a road1 cut out for the most part in a vertical rock-wall4 ,when we observe1 especially from the stream itself1 the details of these sheer valley-sides excavated in limestone1 we again and again detect evidences of solution4 ,high above the present water-level1 the rocks are rounded1 and are often undercut1 so that they overhang 7,fig4 #c74 ,in ,millersdale in ,derbyshire1 above grass-grown taluses1 the surface is still smooth to the hand1 and we can picture the water swirling against it1 and washing it away1 as it does now in the bottom of the grim ravines of ,carniola4 ,it has been suggested1 indeed1 that some limestone caons represent underground waterways1 the roofs of which have fallen in4 ,this may be true of the fine gorge of ,cheddar1 and in some cases is proved by the existence of rock-arches bridging across the hollow of the stream4 ,illustration3 ,fig4 #c4 ,waterworn ,cliff of ,limestone4 ,ravine of ,millersdale1 ,derbyshire4 ,the characters of an unmitigated limestone region are best seen when we travel east of the ,adriatic4 ,here what have been styled the karst landscapes become prominent1 and may be followed through the ,greek isles to the ,levant4 ,something of the kind is realised in the terraced lands between the ,rhne and the upper reaches of the ,durance2 lavender bushes form dull-green spots on almost barren hills1 and the grey walls of old stone-built towns are barely distinguishable against equally grey hillsides4 ,but towards ,trieste the limestone lands are barer still4 ,the small amount of insoluble matter yielded by the rock may accumulate in swallow-holes1 which are here called dolinas1 a ,slavonic word really meaning valleys4 ,this residue appears in the dolinas as a red clayey earth1 the terra rossa of the ,italian-speaking ,dalmatian coast4 ,but on the surface of the plateaus it is washed or blown away as soon as it is extracted from the limestone4 ,a4 ,grund#bh has suggested that the frequency of frost-action in more northern areas allows surfaces of limestone to be cumbered with loose blocks among which soil-patches may gather2 hence we do not find karst-features on the plateaus of central ,bavaria1 ,champagne1 or the ,cotteswold ,hills4 ,something approaching to a karst appears in the wind-swept levels of southern ,galway and of ,clare1 and exposure to strong winds has probably a good deal to do with the origin of the ,causses and the ,illyrian karstlands4 ,at the same time1 the amount of impurity in the limestone must strongly influence the resulting landscape4 ,the noble woods in the limestone hollows of southern ,ireland are rendered possible by the clay soils derived from the limestone1 as much as by the sheltered nature of the ground4 ,illustration3 ,fig4 #d4 ,limestone ,country ,dissected by ,ravines4 ,karstland of ,hercegovina1 from the ,maklen ,pass4 ,in typical karstlands1 water sinks in1 and emerges again on low ground1 where the surface-forms cut the level of the subterranean water-table4 ,streams that manage to hold their own for a time on the uplands often disappear into the clefts4 ,marshes may occur in hollows1 but may have no outlet1 except in vertical directions1 upwards by evaporation and downwards through the dolinas4 ,the dolinas correspond1 as the ,slavonic shepherds so aptly perceived1 to the river-valleys of more normal areas4 ,the landscape of flowing streams has to be sought for in a mysterious underworld1 of which we can gain only a few glimpses4 ,what we know is largely due to explorers of singular enterprise and resource1 notably ,e4 ,a4 ,martel and the spelologists whom he has inspired4 ,a view over the plateau of ,hercegovina shows us how deep gorges1 rather than ordinary river-valleys1 are prevalent where important streams run across a karstland 7,fig4 #d74 ,the roads are carried1 where possible1 along the ravines1 and the country possesses a double life1 that of the broad uplands1 where tanks have to be made to preserve the water1 and that along the commercial highways1 four or five thousand feet below4 ,even beside the rivers there is a sense of desolation in the barren whiteness of the rocks4 ,the sunlight strikes on the wall of some theatre of the limestone1 carved out in old times by a side-swirl of the stream1 and the hollow glares like a white furnace in the hills4 ,the river in summer shrinks among broad stony reaches1 to which thin-flanked sheep are driven for a scanty pasture4 ,its clear green water gives no promise of alluvium for its banks4 ,limestone1 even in temperate ,europe1 may create the features of a desert land4 ,the most extraordinary rock-scenery in ,europe is due to limestone in the dolomitic state4 ,it is not clear if the crags and pinnacles of ,tyrol are caused by the change from calcium carbonate into dolomite1 whereby a granular mass has arisen1 weathering freely along its vertical joints4 ,it may well be that these compact limestones have developed an exceptionally jointed structure under earth-stresses1 and that faulting has intensified their tendency to break up into fort-like blocks4 ,stratified masses of more normal ,rhtic limestones often provide a terraced structure near the mountain-crests2 but in thousands of feet of underlying dolomite vertical clefts prevail entirely over planes of bedding4 ,if1 as is extremely probable1 these dolomite-rocks arose from the composite masses that we style coral-reefs1 stratification was none the less a marked feature as their limestone grew in thickness4 ,this structure is still plainly visible2 but the joints have been widened1 and the mass is cut up into stupendous pinnacles and dominating towers4 ,the ,drei ,zinnen near ,landro1 the deeply notched wall of the ,langkofel and the ,plattkofel1 rising four thousand feet above a grassy upland of normal ,lower ,triassic strata1 and the overhanging crests of the ,sett ,sass above ,buchenstein1 are types of a country where dolomite is pre-eminent1 and where the zone of steep rock-weathering is marked by the most fantastic forms4 ,,on ,,marbles ,any limestone the markings or colour of which render it suitable for ornamental purposes passes as a ,marble4 ,fossil marbles are often mere grey limestones1 in which the stems of crinoids1 or the curved sections of shells1 or the radiating patterns due to corals1 please the eye with their variety on a polished surface4 ,the ,purbeck ,marble that was so much used as a grey foil to the massive white columns of cathedrals throughout ,england is simply a freshwater limestone1 of no great merit as a building stone1 crowded with the shells of ,paludina4 ,the black marbles are limestones coloured by one or two per cent4 of carbon1 derived from the decay of organisms1 and white shells may stand out in them conspicuously1 in contrast with the ground4 ,the red marbles of ,plymouth and of ,cork have become iron-stained1 and at the same time secondary crystallisation has destroyed many of their original features4 ,in ,little ,island1 near ,cork city1 earth-movements have crushed the mass1 which in consequence shows signs of solid flow4 ,the breaking of a crystalline limestone under such stresses furnishes us with many handsome marble ,breccias4 ,the abrupt juxtaposition of angular masses of various colours1 torn from beds originally distinct1 renders some of these rocks almost too startling for the decoration of rooms of moderate size4 ,there seems no such thing in nature as amorphous carbonate of lime1 and all limestones are therefore formed of crystalline particles2 but the further crystallisation of this material produces a true marble1 in which all traces of fossils may be lost4 ,heat and pressure underground probably facilitate this change1 since even soft chalk is converted by igneous dykes into granular marble4 ,but where the pressure is accompanied by the possibility of movement1 the shearing action breaks down the grains1 and a more delicate structure results4 ,we have already seen 7p4 #ce7 how dolomite may undergo striking mineral changes through advanced metamorphic action4 ,lime-garnets1 wollastonite1 diopside1 and other silicates similarly develop in ordinary limestones exposed to the intrusion of an igneous magma4 ,the extreme changes in such rocks will be described when amphibolites are dealt with4 ,,chapter ,,iii ,,the ,,sandstones ,,the ,,origin ,,of ,,sands ,the essential characteristic of ,sandstone is that it consists mainly of detrital grains of quartz1 or occasionally of grains of chalcedonic silica 7flint72 these are found to scratch the steel blade of a knife1 and are not affected by boiling in ordinary acids4 ,the grains usually become cleaner in the boiling process1 since the cement that has bound them together is liable to be destroyed4 ,this cement may cause effervescence1 being often formed of chemically deposited calcium carbonate4 ,when we consider the distribution of quartz in nature1 we look to igneous and metamorphic rocks for the origin of the grains in sandstone4 ,quartz is one of the commonest minerals2 but in granite and quartz-diorite it rarely forms more than half the bulk of the rock1 felspar and mica and hornblende being its associates4 ,veins of quartz 7quartz-rock7 traverse many rocks1 and become broken up into granular forms on weathering2 but they are inconsiderable in comparison with the bulk of the slates or schists in which they lie4 ,mica-schists contribute a good deal of quartz-sand when they decay2 but this is mixed with ferruginous clayey matter1 and the soils produced are yellow loams4 ,we are easily impressed1 then1 by the enormous amount of denudation that was requisite to produce our existing sandstones4 ,though nowadays sandstones can be built up by the decay of older rocks of the same kind1 the quartz must have come originally from igneous or metamorphic sources4 ,even in the metamorphic rocks1 a large part of the quartz is probably detrital4 ,the microscopic characters of the quartz in sandstone commonly attest its origin4 ,the minute liquid inclusions1 with moving bubbles1 that arise in the quartz of igneous and metamorphosed rocks1 are easily seen in sections of sandstone4 ,in some quartzites1 these inclusions run in continuous bands from grain to grain1 and have clearly arisen since the detritus was cemented4 ,but in ordinary sandstones the inclusions in one grain have no relation to those in its neighbours4 ,the felspars1 moreover1 of igneous rocks are commonly found1 as rolled fragments1 in sandstone4 ,their grains are usually whiter and duller than those of quartz1 and may easily be distinguished by the naked eye4 ,small gleaming plates of mica from the parent rock may accumulate with the quartz grains4 ,the dark micas of decaying rocks1 rich in iron and magnesium1 together with mineral silicates of calcium1 magnesium1 and iron1 such as the amphiboles and pyroxenes1 form on hydration soft green chlorite4 ,this mineral1 in films and easily deformed flakes1 at times occurs as a sort of groundwork to the coarser grains in sandstone1 and colours the rock a delicate grey-green4 ,fine-grained sandstones of this type are difficult to distinguish from altered greenstones1 such as basaltic andesites4 ,when the quartz grains1 however1 are large1 as in the grits quaintly styled in old days greywacke1 they form a ready clue to the origin of the rock4 ,nature sifts the products of decay so thoroughly1 on any slope exposed to wind or rain1 that the finest materials are carried far away1 and the undecomposable quartz remains predominant4 ,the alluvium in the upper reaches of streams is thus far more sandy than the mixed material supplied at the outset from the surrounding rocks4 ,the more rapid flow of the water on the steeper upland slopes naturally removes the mud into the lowland4 ,when the detritus1 still somewhat mixed1 reaches a sea-shore1 wave-action is rapidly effective4 ,before the continual wash and pounding of the water1 any residual clay1 and the finely comminuted portion of the quartz1 are carried down the coastal slope4 ,the colour of the sea after storms is sufficient evidence of the work that it performs4 ,beaches1 then1 arrive at a great similarity of type4 ,the inviting yellow sands1 formed of comparatively coarse material1 occur alike off shores formed of chalk1 slate1 granite1 or boulder-clay4 ,illustration3 ,fig4 #e4 ,sand ,developing from ,sandstone1 in semi-arid climate4 ,near ,laingsburg1 ,cape of ,good ,hope4 ,from the beginning of sedimentation1 sands have thus tended to accumulate1 and to become cemented into sandstones4 ,these rocks1 in turn uplifted and exposed1 have yielded other sandstones4 ,since coarse sand does not travel far from the region where it is washed out of the parent rock1 a thick mass of sandstone extending over many square miles may waste away1 and yet become perpetuated in the district4 ,sandiness thus begets sandiness1 and the physical conditions due to the presence of sandstone may prevail through long geological epochs 7,fig4 #e74 ,of course1 a submergence beneath the sea may change all this in a brief time2 but wrinklings of the crust1 raising the sandstones into severer atmospheric levels1 may only accelerate their decay and render the surrounding lands more sandy4 ,,the ,,cementing ,,of ,,sands ,the cement of sandstones is very varied4 ,on our modern coasts1 springs draining from a limestone land1 or even running through banks of broken shells1 will deposit calcite in the interstices of the beach1 until slabs and shelves of conglomerate and sandstone arise in defiance of the waves4 ,on coasts where calcium bicarbonate is abundant1 it may be precipitated by any cause that diminishes its solvent4 ,mere evaporation1 and the escape of carbon dioxide from the water as it is scattered into spray1 lead to the deposition of a cement between the grains of sand4 ,as ,linck#f shows1 calcite is thus laid down in temperate waters1 while aragonite forms fibrous crystals between the detrital fragments on the flanks of tropic isles4 ,aragonite may also arise from the action of ammonium carbonate or sodium carbonate on calcium sulphate or calcium chloride in sea-water4 ,sands thus become cemented by one or other form of calcium carbonate4 ,they include1 moreover1 calcareous alg1 foraminifera1 and fragments of coral and sea-shells4 ,fossil shells are usually represented in older sandstones by mere external and internal moulds4 ,the texture of the rock allows of their being dissolved in percolating waters1 while in clays belonging to the same geological series they may be exquisitely preserved4 ,in shallows1 and especially in lakes1 where soluble salts of iron become readily oxidised1 brown iron rust1 the mineral limonite1 is continually forming at the surface and sinking to the bottom1 where it firmly cements the sand4 ,a group of bacteria#bi extracts iron in this form from the water of freshwater lakes and swamps1 and greatly aids in its accumulation4 ,though a red colour may appear also in marine deposits1 masses of red and purple conglomerates and sandstones may reasonably be assigned a freshwater origin4 ,such rocks are usually found to be devoid of marine fossils1 and they often contain traces of land plants4 ,barytes 7barium sulphate71 which sometimes occurs in veins simulating those of calcite1 is an occasional cement of sandstone1 evidently arising from subterranean waters4 ,bands of flint 7chert7 occur in certain sandstones1 such as the ,hythe ,beds of the ,english ,lower ,greensand ,series4 ,these are due to the cementing of certain layers by chalcedonic silica1 and the source of this silica is seen in the hollow moulds of sponge-spicules1 and the glauconitic casts of their canals1 that commonly remain4 ,g4 ,j4 ,hinde#cj shows that in the ,cretaceous examples1 as in so many other flints1 the majority of the spicules are of the tetractinellid type4 ,under arid conditions1 as in parts of ,africa1 loose superficial sands may become cemented by calcium carbonate1 or even by silica1 brought up in water rising by capillary action from below4 ,the sand-dunes of the coast of our own islands1 which cannot remain wet for long1 become in places toughened by a deposit of calcite derived from the abundant shells of land-snails4 ,in the ,cape of ,good ,hope#ca the dunes1 as ,a4 ,w4 ,rogers states1 are converted by invasions of calcium carbonate1 into hard rock through a distance of many feet from the surface1 and where repeatedly wetted and dried1 as happens where the sea has encroached upon old dunes1 the rock becomes intensely hard and weathers with a peculiarly jagged surface4 ,the ,general ,post ,office and the ,south ,african ,museum in ,cape ,town are mainly constructed of this recently consolidated rock4 ,the modern sandstones cemented by silica are still more interesting4 ,in the ,cape of ,good ,hope1 and notably in the ,kalahari desert1 they form the intensely hard rock known as ,quartzite#cb4 ,the cementing material is true quartz1 which sometimes deposits itself in bipyramidal crystals about the grains of sand4 ,the molecules of such crystals are arranged in continuity with the grouping of those in the original detrital grain1 as is proved in thin sections under the microscope by the optical continuity of the quartz of the grain and of its coating4 ,as silica continues to be deposited1 the coatings interlock1 and the rock passes into true quartzite4 ,it is now often difficult to detect the outline of the original grains4 ,such superficial quartzites may be ten feet thick at most1 with uncemented sand below4 ,rogers suggests that the cementing process may have originated in shallow pools2 but it has obvious analogies with that which forms iron-pans and superficial masses of calcium carbonate in regions where capillary waters are subject to prolonged evaporation4 ,h4 ,g4 ,lyons#cc has attributed the cementing of parts of the ,nubian ,sandstone in the desert of ,lower ,egypt to the silica set free by the alteration of the felspars in the rock4 ,this change1 he suggests1 was accelerated by the infiltration of sodium carbonate of local origin4 ,fossil trees in these strata have been replaced by silica4 ,a further example is recorded by ,armitage#cd from ,victoria1 where friable ferruginous ,cainozoic sands have been converted into quartzite4 ,this type of rock1 the hardest known1 and associated in our minds with high antiquity and metamorphic action1 proves1 then1 to be in process of construction at the surface at the present day4 ,the observations of ,rogers show that quartz and not mere chalcedony is deposited on the grains of sand4 ,the crystalline sandstones of ,permian and ,triassic age in ,england may1 then1 have acquired their remarkable characters at the actual epoch of their accumulation4 ,this is rendered the more probable by the recognised occurrence of arid conditions1 at any rate seasonally1 when the strata in question were laid down4 ,these ,english crystalline sandstones were described by ,h4 ,c4 ,sorby#ce1 who showed that the quartz deposited on the detrital grains was in optical continuity with that of the grains themselves4 ,j4 ,a4 ,phillips#cf regarded this quartz as crystallised out during the kaolinisation of felspars4 ,the phenomena of laterisation1 however1 give us a further suggestion as to the origin of the secondary silica4 ,it is now well known that tropical processes of weathering1 with alternations of wet and dry seasons1 allow alumina to be set free from combination with silica1 lateritic crusts thus arising on a great variety of rocks4 ,the felspars of a sandstone may1 under such conditions1 become laterised rather than kaolinised1 aluminium hydrate being left1 and the silica passing into solution and appearing again in certain layers as cementing quartz4 ,the almost complete disappearance of silica from the more advanced laterites shows that it has been carried away elsewhere1 and the cement of quartzite may thus be derived from rocks at a considerable distance4 ,just1 however1 as the destruction of siliceous sponge-spicules implies the formation of flint1 so laterisation implies silicification as a complementary process4 ,the fact that secondary quartz in quartzite often arises in the rock itself is shown by the frequency of quartz-veins in quartzites1 while they are almost absent from associated slates or schists4 ,hence it appears that a removal of silica goes on at some points1 leading to an infilling of all the cracks and interstices at another4 ,it is clear1 then1 that sandstones1 according to the mode in which they have been affected by percolating waters1 may vary from the crumbling uncemented condition1 known as ,sand-rock1 to that hardest and most resisting of rocks1 quartzite4 ,the permeability of sandstone is responsible for a wide variety of types4 ,,the ,,sand-,,grains ,,of ,,sandstone ,sandstones are originally permeable by water1 not because they possess a high percentage of pore-space1 or porosity1 but because the pores between the grains are large4 ,water can thus move easily by gravitation through the mass4 ,the capillary rise or spread of water is greatest in materials of very fine grain1 though in these it may be extremely slow4 ,for the most effective rise of water against gravity by capillary pull1 a large proportion of particles about #jb mm4 in diameter should be present4 ,sand-grains1 however1 often measure #e mm4 in diameter1 and the fine mud or highly comminuted sand between the coarser matter is the cause of the spread of water through the mass when the supply comes from a subterranean water-table4 ,rain1 however1 is of course readily absorbed4 ,it disappears so rapidly on some barren sandstone areas1 coated as they are by loose sandy soils1 that vegetation cannot make a start1 even where water is supplied4 ,daubre1 ,sorby1 and others have studied the characters of sand-grains1 and it has been pointed out1 that agitated water buoys apart and carries forward by flotation grains with a diameter of #a mm4 or less4 ,hence coarser grains may become rounded like pebbles1 by friction on the bottom of a stream2 but small ones remain angular throughout geological periods1 and even when transferred from one sandstone to another4 ,when their surfaces have been cleaned by boiling in hydrochloric acid1 the sharpness and irregularity of the quartz grains is strikingly apparent4 ,mingled with these grains1 in addition to the minerals previously mentioned1 many interesting crystals appear that have become concentrated in the natural washing processes4 ,minute colourless zircons and brown rutiles1 derived from granite1 have collected1 owing to their high specific gravity1 in certain sands4 ,magnetite and ilmenite may darken the mass2 monazite and thorite1 which are sought after for their constituents cerium and thorium1 become similarly selected in alluvial hollows1 owing to their density of #e4 ,whatever gathers thus in sands may become preserved in sandstones1 and the study of thin sections of the latter under the microscope is fruitful in suggestions as to their origin4 ,some sandstones are remarkable for their highly rounded and almost spherical grains4 ,j4 ,a4 ,phillips#ch compared these with the wind-worn grains of deserts1 which assume similar forms and a considerable polish4 ,large quantities of sand are carried from arid lands into rivers1 into lakes1 or into the sea1 and hence well rounded grains1 in bedded rocks1 and even in marine sandstones1 may have had a desert origin4 ,j4 ,w4 ,judd1 when examining the deposits of ,lower ,egypt for the ,royal ,society1 commented on the extreme freshness of the felspathic particles in sands accumulating in rainless areas1 and recent observations on the soils of semi-arid districts show their comparative poverty in clay4 ,enough has been said to indicate the variety of geographical considerations that may arise from the examination of beds of sandstone4 ,the grains often prove1 especially in the coarser types1 to be fragments of rocks rather than isolated minerals1 and thus furnish a picture of the materials that formed the surface exposed to denudation4 ,the sandstones of finest grain may be found in beds deposited almost on the limits of sedimentation from the land1 where they are interlocked with material of truly pelagic origin4 ,marine muds often contain a high percentage of comminuted quartz1 and the study of shales and slates of ancient days shows how this almost indestructible mineral finds its way into beds that might easily be classified as clays#da4 ,,some ,,characters ,,of ,,sandstone ,earth-stresses and shrinkage give rise to joints in sandstone1 which may not be so clean and sheer as those in limestone1 but which affect even the softer forms4 ,cemented sand-dunes of modern date tend to break away along vertical planes4 ,firmer sandstones give rise to stepped table-lands and edges1 and the resistance of many types to atmospheric decay renders their stratified structure strongly apparent4 ,small intervals in the process of deposition1 or slight changes in the coarseness of the sand brought down by currents1 give rise to laminated and flaggy types4 ,where a broad shore has been exposed between tide-marks1 the drying and compacting of the surface before the next layer is laid down enables the latter to take a mould of the inequalities of that below4 ,ripple-marks1 sun-cracks1 rain-prints1 and the footmarks of animals1 are often preserved in this manner4 ,where the shore is subsiding1 they may persist through hundreds of feet of strata4 ,naturally1 the best examples of these casts1 and of the original structure in the underlying bed1 occur where a little mud has been laid down over the sandy flat4 ,clay by itself1 if damp1 does not retain the impressions sufficiently long1 and1 when once thoroughly dried1 it crumbles when the next water overflows it4 ,but a foundation of firm sand with a thin mud-layer on its surface1 as may be recognised in some ,triassic deposits1 furnishes excellent records of local weather or of the movements of errant animals4 ,on the flat shores of lakes in a semi-arid climate1 the water may retreat for miles1 and return1 perhaps months afterwards1 when rains in the hills have given it a new burden of detritus4 ,under such conditions1 broad sun-cracked flats may be preserved1 with perhaps some plant-remains between successive layers#ich4 ,the castings and tracks of worms1 and the tubes of boring species1 which are sometimes infilled by sand of a different colour1 are common in sandstones of all ages4 ,,siliceous ,,conglomerates ,the deposits of wave-swept beaches leave us ,conglomerates formed of various types of pebbles1 among which quartz-rock and quartzite naturally predominate4 ,in some cases the pebbles are ready formed when they reach their resting-place4 ,they come rolling out from lateral torrents into the quieter waters of a main valley1 as may be seen in summer in the broad pebble-banks of the north ,italian streams4 ,thence they are washed by occasional floods into the great confluent deltas that constitute the upper part of an alluvial plain1 or into lake-basins1 where they promptly settle along the shore4 ,but few such pebbles1 except from pre-existing conglomerates or gravels on the shore-line1 actually reach the sea4 ,the rolled stones upon sea-beaches are mostly the products of marine action on the spot4 ,while the fine sand-grains go seaward almost unharmed1 the detrital stones1 offering far less surface in proportion to their mass1 strike on their neighbours as every wave shifts them on the beach1 and soon assume a rounded form4 ,the conglomerates ultimately consolidated may reveal stratification only by the general arrangement of their pebbles4 ,these can rarely be spheres1 since they are not as a rule turned over1 but are pushed this way and that until they acquire a flat ellipsoidal shape4 ,they lie with their flatter sides in planes parallel to one another4 ,generally1 however1 alternations of coarser and finer beds mark out the stratification even in conglomerates4 ,the sands of deserts include abundant stones and blocks of rock1 and the loose material becomes1 moreover1 sifted by the wind4 ,true desert sands may accumulate at one point1 the very finest loamy material may be carried away still farther to form fields of fertile lss1 and a rock-desert1 formed of stones resting on bare surfaces1 may remain in large areas of the arid region4 ,the loose stones here assume a characteristic shape1 and have been known under the ,german name of ,dreikanter4 ,they are fairly flat below1 and are cut away above by the drifting sand into a form resembling a gable roof dipping at both ends4 ,their surfaces are characteristically etched4 ,dreikanter have been found in beds that were formerly ascribed to deposition on the shores of lakes1 and it must now be borne in mind that continued attrition by drifting sand affects mixed detritus on a land surface much as the wash of waters does upon a beach4 ,certain materials are cut away more rapidly than others1 and the residue assumes a more and more quartzose type4 ,in this way1 sandstones1 and conglomerates in which fragments of quartzite and vein-quartz predominate over other constituents1 may arise as olian beaches on dry land4 ,,sandstone ,,and ,,the ,,land-,,surface ,the permeability of sandstone has already been referred to4 ,the surface offered by it is typically dry1 and the soil1 consisting mainly of grains of siliceous sand1 can neither retain the rain that falls nor draw up water from below4 ,the idea that trees can flourish on sandstone soils because they require nothing from the soil itself is of course erroneous4 ,they depend to a large extent upon the materials set free by the decay of certain grains1 or of the cement of the underlying sandstone4 ,in proportion as the sandstone is impure1 that is1 the more its constituents deviate from pure quartz1 the more chance there is that it will provide a fertile soil4 ,on the whole1 however1 areas of siliceous conglomerate and sandstone are given over1 even in temperate climates1 to forest and heather4 ,where the sandstone is still in the sand-rock state1 bare patches are likely to appear even in the heath that has grown across it1 and from these the wind carries away shifting sands4 ,everyone familiar with the ,carboniferous areas of the ,english midlands will realise the influence of hard grit and sandstone in forming edges across the country4 ,the contrast between these escarpments and the slopes of crumbling shale that often underlie them gives diversity to the scenery of ,yoredale and the ,peak4 ,the more yielding sandstones of ,cretaceous age round about the ,weald1 or at the foot of the ,chiltern ,hills near ,woburn1 form rounded hills1 mostly clad with woods of coniferous trees4 ,in ,surrey1 unpaved cart-tracks1 used for centuries1 have cut gullies in the unconsolidated ,folkestone ,sands4 ,the underlying ,hythe ,beds1 however1 stand out between ,reigate and ,guildford as a bold escarpment1 and it is interesting to reflect that this fine feature of south-eastern ,england is probably due to the chert which the beds contain 7see p4 #fb74 ,the local growth of siliceous sponges in a ,lower ,cretaceous sea enables ,leith ,hill in our days to dominate even the arch of ,ashdown ,forest1 where another unfilled sandstone area rises in the centre of the ,weald4 ,the sands of ,bagshot ,heath1 and numerous similar areas in the ,paris ,basin1 show how impossible it is to cultivate such strata1 even near the best of markets4 ,the flint gravels that cover much of the upland in the ,new ,forest may also be borne in mind1 as presenting the worst features of highly siliceous lands4 ,in a semi-arid climate1 or one with only seasonal rains1 the processes by which sandstone begets sandstone tend to develop desert wastes4 ,the soils produced by weathering do not cake together1 and are carried away by wind during the drier months4 ,the bare rock appears over broad surfaces1 just as it does in storm-swept limestone areas1 and any hollow where shelter is afforded tends to become filled with sand 7see ,fig4 #e74 ,the hummocky and extremely irregular surface of some of our ,silurian areas1 such as parts of the ,southern ,uplands of ,scotland and the hard-won farmlands of ,down and eastern ,monaghan1 is due to the presence of resisting sandstones among the shales4 ,these sandstones1 passing into true grits1 are repeatedly folded1 and their upturned edges have resisted even the passage of glacier-ice4 ,they jut out along the crests of ridges1 and even the smaller beds furnish angular fragments to the soils4 ,illustration3 ,fig4 #f4 ,siliceous ,conglomerate4 ,characteristic weathering2 moraine-blocks at ,coumshingaun1 ,co4 ,waterford4 ,far wilder scenery is formed by the more continuous sandstone masses of the ,harlech ,beds in western ,wales1 which are grits so firmly cemented that the rock breaks across the quartz-grains4 ,much of the ,old ,red ,sandstone is of equally hard quality 7,fig4 #f74 ,its purple or grey conglomerates1 the pebbles of which are quartzite in a quartz cement1 form bare and rugged masses in the ,great ,glen south-west of ,inverness1 and are responsible in ,kerry for some of the wildest rock-scenery in the ,british ,isles4 ,variations in coarseness allow of the development of a marked stratification on the weathered mountain sides1 and differential erosion of the beds has taken place where ice has pressed against them4 ,even on precipices1 grassy ledges may occur1 marking bands of sandstone or shale in the conglomeratic mass4 ,the red sandstones and conglomerates that form huge outstanding bluffs from ,applecross to the north of ,sutherland represent the denudation of a pre-,cambrian mountain region4 ,these ,torridon ,sandstones cover a very irregular surface of old gneiss1 with which their almost level strata are in striking contrast4 ,p4 ,lake#ci has compared them with the deposits styled dasht in ,baluchistan and ,afghanistan1 which similarly fill up valleys and cover hills1 as products of extensive and rapid denudation4 ,there is much1 indeed1 to suggest that the ,torridon ,sandstone1 some #aj1jjj feet in thickness1 was accumulated in a dry country on a continental surface1 with the aid of floods during occasional rainy seasons4 ,quartzite1 which fractures into small angular blocks under earth stresses1 yields an intractable surface of bare rock and taluses of shifting stones4 ,the latter sometimes crumble down into white sand1 which provides some basis for the growth of heather4 ,the numerous joints1 independent of the bedding-planes1 cause the rock to break up almost equally on any exposed slope1 and the crests of quartzite hills become typically converted into cones 7,fig4 #g74 ,viewed from a distance1 the white taluses1 streaming down evenly from the crests1 resemble caps of snow4 ,illustration3 ,fig4 #g4 ,quartzite ,cone4 ,croagh ,patrick1 ,co4 ,mayo4 ,the absence of soil and the smoothness of weathered surfaces render quartzite mountains hard to climb4 ,the uniform cementing of the rock leaves the bedding with little influence on the surface-features1 and rock-ledges and shelves are rare4 ,the traveller ascends over taluses of angular and obstinate blocks towards slippery and inhospitable domes4 ,but the wildness of the scenery will be his sure reward4 ,it is of interest to reflect that the material of these bold outstanding mountains may in certain cases have originated1 in all its hardness1 in the levels of a sun-parched plain4 ,,chapter ,,iv ,,clays1 ,,shales1 ,,and ,,slates ,,characters ,,of ,,clay ,,and ,,shale ,the question of what is a true ,clay has been much discussed1 especially by agriculturists1 in recent years#ici4 ,the material1 as a rock1 is regarded as a massive kaolin1 and1 if pure1 should have the following percentage composition3--silica #dfc1 alumina #cih1 water #aci4 ,some ,pipe-clays1 white and uncontaminated1 closely approximate to this ideal4 ,true clays are very plastic when moistened1 and shrink on drying1 forming a compact mass the particles of which do not fall apart4 ,when thoroughly dried1 however1 and placed in water1 lumps of clay break up readily2 the water creeps in along their capillary passages and expels trains of air-bubbles as it goes4 ,this fact has been utilised in the extraction of fossils from a matrix of stiff clay4 ,if the clay thus reduced to powder is now puddled by the finger1 it again forms a closely adherent plastic mass4 ,the individual spaces between adjacent particles in a clay are very minute1 and this accounts for its practical impermeability to water2 but the total pore-space or porosity may amount to more than fifty per cent4 of the volume of the rock4 ,unless earth-pressures have brought the mass into the condition of shale or slate1 the tiny flaky kaolin particles1 and the associated very small grains of other minerals1 have not shaken themselves down into a closely aggregated state4 ,when moistened1 however1 and again dried1 the surface-tension of the film of water about any group of grains1 increasing as evaporation thins the film1 draws the grains nearer to one another1 and a considerable shrinkage of the mass results4 ,alternate wetting and drying tends to make a clay less obdurate and sticky1 by increasing the number of separate aggregates of grains4 ,the passages between these aggregates are no longer so minutely capillary1 and a clay soil becomes by this process distinctly lighter from the farming point of view4 ,the larger cracks caused by shrinkage greatly increase the evaporation of water1 by exposing new surfaces1 which penetrate deeply into the clay4 ,often the mass shrinks so as to develop hexagonal structure1 from the drying surface downwards 7,fig4 #h74 ,the natural flocculation of clays1 the process by which compound grains are formed in place of individual soil-particles1 is assisted by the action of water bearing certain salts in solution4 ,calcium carbonate is an excellent flocculator1 and this fact has long led farmers to place burnt lime or powdered limestone on their lands4 ,sodium carbonate1 on the other hand1 is brought up in some dry regions by capillary action1 and exercises a reverse effect1 keeping the minute particles apart from one another1 and thus promoting thorough clayiness in the clay4 ,experiment has shown that fineness of grain is responsible for most of the characters of a clay1 and from this point of view the small size of kaolin flakes as compared with grains of other minerals will account for the clayiness of this particular mineral when it constitutes a rock4 ,clays1 however1 when shaken up in a column of distilled water1 cause what seems to be a perpetual cloudiness1 since it remains after the great bulk of the clay has settled down4 ,flocculation by salts alone removes it4 ,some authors have urged that a colloid substance1 amounting perhaps to only one or two per cent4 of the whole clay1 imparts this distinctive character4 ,such colloids are believed to arise during the decomposition of aluminous silicates under tropical and probably alkaline influences2 but they are not known to be associated with the processes by which kaolin is formed from felspars4 ,illustration3 ,fig4 #h4 ,shrinkage-cracks in ,clay1 with footprints of birds in the foreground4 ,tundra of ,mimer ,bay1 ,spitsbergen4 ,a4 ,d4 ,hall#dj points out that the cloudiness is probably due to the extreme minuteness of certain of the particles4 ,true clayiness thus depends on the proportion of grains smaller than #jjb mm4 in diameter4 ,yet ,hall and ,russell look to other causes to explain the continued suspension of such particles in the water1 and they suggest the presence of potassium and sodium silicates of the zeolite group1 which liberate by hydrolysis a little alkali in contact with a large bulk of water4 ,free alkalies prevent flocculation1 and so encourage suspension of the particles4 ,to the ordinary observer1 a rock possesses the properties of clay1 and is a clay1 if it contains more than forty per cent4 of particles less than #ja mm4 in diameter4 ,but such rocks are found1 on chemical analysis1 to contain a large amount of kaolin1 and the old view1 that clays are massive kaolins1 is thus substantially correct4 ,none the less1 clays are notably impure1 and in many there is a large admixture of quartz sand4 ,the kaolin1 derived originally from the decay of other silicates1 is rarely freed from a variety of minerals and rock-fragments that were associated with it in its place of origin4 ,grains of quartz and unaltered felspar a tenth of a millimetre in diameter distinctly lighten a clay soil1 on account of their relative coarseness4 ,a sandy clay is styled a ,loam1 and a fine-grained loam furnishes the ideal soil for the general purposes of a farmer4 ,it does not retain water too long upon its surface1 nor does it dry too quickly after rain4 ,much of what we call boulder-clay proves to be in reality a loam4 ,t4 ,mellard ,reade and ,p4 ,holland#da have shown that even in clays of marine origin there may be a considerable proportion of very fine quartz sand4 ,calcium carbonate1 usually occurring as fine rock-dust derived from limestone1 or as minute shell-fragments1 may be mingled with clay to form a ,marl4 ,the term is not a quantitative one1 and may be applied to any clay that shows a brisk effervescence with cold acids4 ,though unpleasantly sticky when wet1 marls flocculate themselves naturally by supplying calcium carbonate in solution to waters that pass through their crevices 7see p4 #hj74 ,the stratification of clays may be invisible throughout considerable masses1 unless sandy beds are intercalated among them4 ,yet1 when a lump of clay is dried and then placed in water1 as previously described1 it will often break up along parallel planes1 which show that there is a regular arrangement of its particles4 ,the fact that so many of these particles are platy becomes emphasised under the pressure of subsequent sediments1 whereby the platy surfaces of the particles are brought into planes parallel with one another4 ,the clay then becomes a ,shale1 with regular planes of fissility1 which are parallel to those of bedding4 ,a certain amount of deformation of the rock accompanies this change1 flow being set up parallel with the bedding1 and included fossils becoming sometimes flattened4 ,this deformation is especially noticeable in the case of plant-remains4 ,shales may in time attain the density and fissile structure of true slate4 ,the colours of clays and shales are of considerable interest4 ,blackness is often due to organic matter1 and especially to fragments of plants1 which retain their woody structure and their carbonaceous character when protected by clay from oxidation4 ,the bluish tint of clays is due to finely divided iron pyrites 7iron disulphide71 which may occasionally appear as distinct crystals or nodules of one or other of its forms1 pyrite or marcasite4 ,on oxidation1 limonite arises1 which colours the mass brown1 as is seen in the upper part of many clay-pits4 ,the occurrence of iron pyrites often dates back to the time at which the clay accumulated4 ,n4 ,andrussow#db points out that in the ,black ,sea there is an enormous supply of decaying organic matter provided by the floating organisms of the upper layers4 ,this rains continually down towards the floor4 ,the portion that reaches depths of over #ajj fathoms escapes from the voracity of free-swimming organisms and arrives at the region where bacteria alone abound4 ,these bacteria act on dissolved sulphates1 and also largely1 according to ,andrussow1 on the albumen of the decaying matter4 ,in both cases1 sulphuretted hydrogen is produced4 ,andrussow treats the reduction of the marine sulphates as a minor process1 due to the need that the bacteria have for oxygen in the deep waters1 which are insufficiently supplied4 ,the sulphuretted hydrogen attacks the salts of iron1 and iron disulphide results4 ,here we have an excellent illustration of how1 in deep basins1 with imperfect vertical circulation1 black pyritous muds may arise1 devoid of ordinary fossils4 ,the depths of the ,black ,sea are practically poisoned by the abundance of sulphuretted hydrogen4 ,but numerous cases of shales are known to us where iron pyrites replaces the shells of ammonites or forms complete casts of bivalves1 and has accumulated also in concretions and crystalline groups4 ,such pyrites is probably of secondary origin1 or arose from the reducing action of decaying organic matter on ferrous sulphate in solution in the sea4 ,the oxidation of iron pyrites in shales gives rise to aluminium sulphates1 such as alums4 ,sometimes sufficient heat is evolved during this oxidation to set on fire carbonaceous matter present in the rock4 ,pink-purple and green are common colours among shales1 and imply that the iron is in two different states of oxidation4 ,when the colour varies thus in successive bands1 we may believe that a climatic change promoted the formation of ferric salts on the land surface when the pink layers were being formed1 while ferrous 7less oxidised7 salts predominated when the green particles were washed into the basin4 ,b4 ,smith#dc suggests that the organic matter and humic acids which are swept down in times of flood may temporarily prevent oxidation from occurring in shallow lakes and pools4 ,dry seasons would thus lead to the deposition of pink clays1 while wet seasons would furnish green ones4 ,the green colour in shales is mostly due to chlorite or to glauconite4 ,subsequent deoxidation has been invoked to account for the green colour of certain shales4 ,organic matter may have been responsible1 and the green spots in purple slates have been attributed to the decay of entombed organisms1 the reaction having spread outwards from a centre4 ,clays1 owing to their impermeability1 preserve fossils excellently1 and the oldest shells and corals in which the original aragonite has escaped conversion into calcite occur in clays and shales of ,mesozoic age 7see p4 #bb74 ,,origin ,,of ,,clays ,something has been said on this matter in the foregoing paragraphs4 ,it is now recognised that a pure china-clay or a pipe-clay1 that is1 a pure kaolin-earth1 does not arise from the sifting of the products of surface-denudation4 ,the alkali felspars decompose as they lie in exposed layers of granite and gneiss1 but the kaolin thus formed under the acid action of atmospheric waters is relatively small in quantity1 and cannot escape from its coarser associates1 such as undecomposed felspar and quartz1 until it is carried away far from land4 ,even then1 as the records of ,h4,m4,s4 ,challenger show#dd1 marine muds may contain more than fifty per cent4 of detrital quartz-grains1 and quartz is always the most abundant mineral among the larger particles of the mud4 ,where1 however1 decomposition of the granitoid rock has been exceptionally thorough1 kaolin may be present in sufficient quantity to predominate over other materials4 ,the product washed from the surface then gathers as a white clay even in lakes1 and further artificial washing may extract from it an actual kaolin-earth or china-clay4 ,in such cases1 the rock has become rotted throughout in consequence of subterranean action4 ,hydrofluoric acid as well as other gases have been at work1 as is shown by the secondary minerals associated with the kaolin2 and the appearance of white powdery kaolin in unusual abundance on the surface is due to the local exposure of a mass that was long ago made ready in the depths4 ,the sifting action1 however1 of running waters1 and especially of the sea upon a shore1 ultimately causes clayey matter to be carried away into regions where it is slowly deposited4 ,the flocculating action of the salts dissolved in sea-water greatly assists the precipitation of clay before it has reached some two hundred miles from land4 ,however1 just as sandstone begets sandstone1 clays or shales exposed upon a coast produce new clays close to shore4 ,the estuary of the ,thames and many slob-lands serve as examples4 ,off ,brazil1 red clays arise#de from the large quantity of ochreous matter carried from the coast4 ,modern green marine muds are found to contain glauconite1 a silicate common in the ,english ,gault clays1 and formed by interactions in the sea itself4 ,modern blue muds#df are recorded down to #bhjj fathoms1 and contain organic matter and iron disulphide4 ,much has been written by the observers on the ,challenger and by others on the red clay of truly abyssal depths1 which is attributed to the decay of wind-borne volcanic dust1 and of igneous matter erupted on the sea-floor1 rather than to any direct transport by water from the land4 ,clays may also accumulate on a land-surface from fine volcanic ash1 which decomposes through the action of percolating waters4 ,,slate ,the relations between shale and ,slate are so obvious that slate may readily be regarded as a very well-compacted mud4 ,the clayey material in it1 like that of muds1 may be ordinary detritus or of volcanic origin2 its colours repeat those of shales4 ,its essential character1 however1 is the possession of a cleavage1 that is1 of well-developed planes of fissility1 which are often inclined to those of bedding4 ,the bedding may be indicated by bands of different coarseness or constitution1 and these may show crumpling due to pressure that has been exerted on the mass4 ,the cleavage1 however1 may run right across these bands1 and the rock1 as a rule1 splits far more cleanly along the cleavage-planes than a shale does along its planes of bedding4 ,the early and historic observations on slaty cleavage have been excellently reviewed by ,a4 ,harker#dg1 who also provides an independent investigation4 ,reference may also be made to a later treatise by ,c4 ,k4 ,leith#dh1 which contains numerous illustrations1 and to a discussion by ,g4 ,w4 ,lamplugh#di4 ,d4 ,sharpe and ,h4 ,c4 ,sorby1 between #ahdg and #ahec1 developed the theory that rock-cleavage was due to compression in a direction perpendicular to the planes of cleavage and to expansion along them4 ,as ,harker points out1 it is unlikely that the expansion balances the compression4 ,the density of slate1 about #bg1 is a good indication that the porosity1 or percentage of pore-space1 has been reduced1 while the mineral changes1 soon to be referred to1 are also in favour of greater density4 ,c4 ,darwin#ej laid stress on the connexion between cleavage and the development of flaky minerals1 such as micas1 along the cleavage-planes1 the structure ultimately passing into that known as foliation 7see p4 #ade74 ,h4 ,c4 ,sorby urged that compression brings platy particles into parallel positions throughout the mass1 so that the plates1 which may consist of kaolin1 mica1 or chlorite1 come to lie with their broad surfaces perpendicular to the direction of compression4 ,at the same time1 any constituents capable of deformation become compressed in this direction1 become expanded in a direction perpendicular to it1 and are themselves converted into lens-like forms or plates4 ,t4 ,mellard ,reade and ,p4 ,holland#ea have emphasised the part played by crystallisation at the close of the process of compression4 ,they urge that the platy minerals1 mica and chlorite1 are produced during the alteration of the rock1 and can spread with ease in directions perpendicular to that of compression2 they thus give rise to slaty cleavage at a late stage in the deformation of the rock4 ,these authors1 it will be seen1 have developed one of ,darwin's principal propositions1 as to the close connexion between rock-cleavage and foliation1 and1 in opposition to ,sorby1 consider the platiness of the original constituents to be of less importance4 ,in support of their view1 in regard to the late stage at which cleavage is induced1 it may be noted that the crystals of pyrite and magnetite that sometimes occur in slates and in the allied foliated schists have developed at an earlier date as knots which oppose the cleavage or the foliation#eb4 ,darwin observed that mineral differences sometimes occur along bands parallel with the cleavage-planes4 ,in such cases1 the difference may be largely one of grain1 shearing having broken down the minerals into a finer state along certain bands of movement#ec4 ,shearing of the rock may occur along any of the cleavage-planes1 which are superinduced planes of weakness1 and parts of the slate thus slide over others1 just as the mineral flakes slide over one another in the directions in which expansion of the rock is possible4 ,where traces of the original stratification remain1 it is easy to see if rock-shearing has occurred4 ,beds of different composition naturally take on cleavage in very different degrees4 ,sandy layers show the compression that has taken place by contorting2 but they cleave very poorly1 and in proportion to the amount of mud present in them4 ,where clayey and sandy layers alternate1 and the direction of the cleavage is oblique to them1 it is refracted1 as it were1 on passing from one layer to the other2 it is more highly inclined to the bedding in the sandy layers and less so in the clayey layers4 ,hence a cleavage-surface forms a fold resembling the shape of an italic ,s as it traverses each harder bed4 ,harker#ed and ,leith#ee discuss the cause of this from somewhat different points of view4 ,it is probable that such cleavage-planes as develop within the hard bed are approximately perpendicular to the direction in which the compressive force acts1 because there is in such beds little possibility of lateral creep of the material along the bedding-planes4 ,in the softer layers1 we have to deal1 not only with a tendency towards the rotation of platy particles until their flat surfaces are perpendicular to the direction of pressure1 but also with a tendency of the same particles to flow along the bedding-planes4 ,the resultant arrangement gives rise to a cleavage nearer to the bedding-planes than that in the more sandy layers4 ,sometimes1 after the cleavage is established1 compression folds it1 just as strata may be folded4 ,still greater compression may obliterate it and establish a new cleavage1 and all gradations towards this result are traceable4 ,the cleavage layers1 again1 may be wrinkled into a series of sharp folds1 thrust over in one direction1 and parting may then take place along the ridges of these folds1 which furnish a second series of planes of weakness in the rock4 ,this type of separation has been styled a strain-slip cleavage1 and by ,leith a fracture-cleavage1 in distinction from ordinary or flow-cleavage4 ,shearing may take place along it1 and the true or flow cleavage-planes become thus broken across and faulted4 ,illustration3 ,fig4 #i4 ,landslide of ,limestone over ,shale4 ,near ,luc-en-,diois1 ,drme1 ,france4 ,the scale is shown by the main road passing among the blocks4 ,commercial slates should exhibit none of these structures that interfere with genuine cleavage4 ,an argillaceous rock of uniform grain1 compressed evenly over a considerable district1 is required for successful slate-quarries4 ,yet all quarrymen will admit that the material varies from point to point1 and that the best slate runs in veins4 ,some of the coarser slates1 with irregular surfaces1 and with splashes of colour1 such as are provided by limonite1 are sought after for their picturesque effect2 while slates which do not split readily enough for roofing purposes may have their use for flags1 mantel-shelves1 and billiard-tables4 ,,argillaceous ,,rocks ,,in ,,the ,,field ,obviously1 nothing can be more different than the features of a country made of clay1 when acted on by denudation1 and those of one where slate prevails4 ,in the former case1 low rounded hills rise1 without any definite arrangement1 above hollows where rushes spring amid the grass4 ,the streams are muddy1 and they readily cut their way down to base-level1 meandering thenceforward in a clay-alluvium4 ,shales provide bolder features1 but crumble rapidly where the climate permits of frost and thawing4 ,they may be protected by more resisting rocks1 but provide oozy surfaces underground1 over which the higher masses may slide disastrously 7,fig4 #i74 ,illustration3 ,fig4 #aj4 ,weathering of ,shale4 ,granite mountains behind4 ,above ,la ,grave1 ,lautaret ,pass1 ,isre1 ,france4 ,shale-beds1 when uplifted and folded1 slip away in flakes from one another1 supplying very ragged and irregular material to the taluses1 and exposing shimmering surfaces when damp with rain 7,fig4 #aj74 ,among hilly lands1 the passes will often be found to be due to bands of shale1 which are cut down by weathering far sooner than the rocks on either hand4 ,in central ,england1 the ,lias shales1 despite the presence of some limestones1 have been worn down almost to a plain1 wherever the overlying ,middle ,jurassic limestone has been removed4 ,slates1 with their ragged edges and resistance to rain1 play their part in wilder mountain-scenery4 ,frost-action destroys them1 producing taluses that slip frequently towards the valleys2 but the residual crags assume more serrated forms1 in contrast with the smooth covering of the lower slopes4 ,the cleavage1 when steeply inclined to the horizontal1 promotes the cutting of gullies down the mountain-sides1 and the intervening ribs of rock may easily be mistaken for uptilted strata4 ,the entrance to the ,pass of ,llanberis at ,dolbadarn is a fine picture of slate-scenery4 ,eventually1 mountains formed of slate assume hog-backed and rounded forms1 but they still1 where notched by streamlets1 yield sheer cliffs and picturesque ravines4 ,,on ,,boulder-,,clay ,the material known as ,boulder-,clay presents such distinctive features1 and is so prevalent in our islands1 that it deserves a few separate remarks4 ,from a coating a foot or two in thickness1 it swells in places to a hundred feet or more1 and may form the important round-backed hills to which ,maxwell ,close reserved the name of drumlins4 ,illustration3 ,fig4 #aa4 ,boulder-,clay1 ,crich1 ,derbyshire4 ,it consists essentially of mixed materials1 unsifted by water1 huge boulders of various rocks occurring side by side with angular fragments and pebbles of all sizes1 set in a groundwork of loamy clay 7,fig4 #aa74 ,sands and gravels are often associated with the boulder-clay1 and result from the local washing of the mass in copious floods of water4 ,the blocks are here on the whole more rounded1 and the sandy part of the loam predominates4 ,blocks of shale and limestone1 and even of sandstone and quartzite1 occurring in the boulder-clay1 bear the characteristic striations that we now recognise as due to glacial action4 ,the sand and small stones have1 in fact1 been held against the larger ones by solid ice1 and have cut and grooved their surfaces4 ,shales and schists have gone to pieces and have provided the clayey groundwork4 ,the whole of the material has been at one time embedded in and moved forward by glacier-ice4 ,illustration3 ,fig4 #ab4 ,arctic ,glacier charged with stones and clay4 ,side of the ,nordenskild ,glacier1 ,billen ,bay1 ,spitsbergen4 ,the top of the ice appears in the left-hand upper corner of the picture4 ,though ,louis ,agassiz developed his glacial theory from studies in ,switzerland1 he possessed an imagination that ran before the knowledge of his time4 ,swiss glaciers are now so limited that they are of very little use to us when we seek to explain the origin of boulder-clay4 ,in arctic and antarctic lands1 however1 we meet with continental glaciers1 many miles in width1 moving across lowlands1 in virtue of the pressure from some great snow-dome1 to which additions are continually being made behind them4 ,even when fed by diminished snow-fields1 like those in ,spitsbergen1 these glaciers dominate the landscape and form the principal rock-masses over hundreds of square miles4 ,such glaciers gather into their lower portions all the loosened material on the hill-slopes and valley-floors4 ,with the tools thus supplied1 further material is plucked from jointed or fissile rocks as the mass moves forward4 ,freezing and thawing at the base of the great ice-sheet1 as water flows here and there beneath it1 further disintegrate the rocky floor4 ,the broad ice-sheet sinks in a mass of broken rock and sludge at one point1 and at another drags this mixed material forward as an abrading agent4 ,the lower half of such a glacier1 or the whole thickness of it near its front1 where surface-melting has removed the higher layers1 is in reality an agglomerate of stones and mud held together by an ice-cement 7,fig4 #ab74 ,when an epoch of advance is over1 when the ice-sheet stagnates and its frozen constituent melts away1 it becomes more and more like a boulder-clay as time goes on4 ,true boulder-clay then forms its surface1 while ice remains plentiful below4 ,illustration3 ,fig4 #ac4 ,arctic ,glacier and ,boulder-,clay4 ,the ,sefstrm ,glacier1 ,ekman ,bay1 ,spitsbergen1 in #aiaj1 with boulder-clay in foreground1 marked by kettle-holes1 and deposited by an advance of the glacier over ,cora ,island in #ahif4 ,since the stony matter is not evenly distributed1 some parts of the surface sink more quickly than others1 through loss of a greater portion of their former bulk4 ,roughly circular pits or kettle-holes appear1 in which water gathers4 ,the water running from these washes across a part of the boulder-clay1 bears off the mud1 and leaves bands of sand and gravel4 ,the clayey portion thus removed may accumulate as a fine deposit in other outlying pools1 and is interstratified1 when the flow of water is temporarily increased1 with coarser and more sandy layers4 ,ultimately1 the frozen water of the groundwork drains away1 and only the stones and clay of the ice-sheet remain upon the field4 ,they form1 however1 a very important residue1 weathering in steep cliffs and pinnacles in the dry air of the arctic lands4 ,the boulder-clay thus left shows a sharply marked boundary where the edge of the stagnating ice-sheet lay4 ,it is1 in fact1 the surviving part of the complex sheet1 and now undergoes moulding1 like other rocks1 by atmospheric agencies 7,fig4 #ac74 ,many interesting features of the hills called drumlins cannot be discussed here4 ,their arrangement with their longer axes in the direction of the movement of the ice shows that they were moulded in large measure within the ice itself1 and came to light as it melted away from above downwards4 ,they may be regarded as originating in tough and mixed materials1 ice and stones and clay1 from the lower layers of the ice-sheet1 which became associated with the purer upper ice in certain episodes of the flow4 ,such mingling may occur at an ice-fall1 or where shearing over an obstacle takes place4 ,in the former case1 the upper ice descends into the lower layers2 in the latter1 masses from below are pushed up into higher levels4 ,as the forward flow proceeds1 the masses representing the lower and stone-filled layers are treated just as eyes of coarser material are treated in a fluidal lava or in a rock deformed by metamorphic pressures4 ,the purer and more plastic ice moves past and round them1 and they assume an elongated form#ef4 ,when final stagnation and melting have gone on1 these masses are still separated from one another as rounded hills4 ,their bases have settled down upon the ice-worn surface1 but their flanks and crests retain traces of the moulding action of the purer portions of the complex body styled an ice-sheet4 ,in recent years great interest has been aroused by researches on boulder-clays of ancient date1 especially those of ,permo-,carboniferous age#eg4 ,these compacted deposits contain abundant striated boulders1 and rest on glaciated rock-surfaces1 which have a surprisingly modern aspect when laid bare by denudation4 ,the grey-green ,dwyka ,conglomerate that is so widely spread throughout ,south ,africa forms kopjes on the borders of the ,great ,karroo1 with spiky crests and irregularly weathered cliffs2 but its original deposition as a boulder-clay has been amply verified4 ,it has now1 moreover1 been paralleled by a very similar rock discovered by ,a4 ,c4 ,coleman in the ,huronian beds of ,canada4 ,,chapter ,v ,,igneous ,,rocks ,,introduction#eh ,igneous rocks1 those varied masses that have consolidated from a state of fusion1 attracted attention in the eighteenth century through their active appearance in volcanoes4 ,james ,hutton in #aghe showed that the crystalline granite of the ,scottish highlands had been made to invade that country in a fluid state4 ,more than a hundred years1 however1 elapsed before geologists on the continent of ,europe were willing to connect superficial lavas with the materials exposed by denudation in consolidated cauldrons of the crust4 ,it is interesting therefore to note that ,g4 ,p4 ,scrope in #ahbe treated of granite1 without apology or hesitation1 in a work entitled ,considerations on ,volcanoes4 ,so far from separating deep-seated from superficial products1 ,scrope wrote of the molten magma in the crust as the general subterranean bed of lava4 ,he conceived this fundamental magma1 the original or mother-rock1 to be capable of consolidating as ordinary granite4 ,successive meltings and physical modifications of this granite gave rise1 in his view1 to all the other igneous rocks4 ,scrope laid no stress1 however1 on chemical variations within the magma1 but urged that the transitions observable between different types of igneous material established a community of origin4 ,the connexion between lavas and highly crystalline deep-seated rocks1 so simply accepted by ,scrope1 was worked out some fifty years later by ,j4 ,w4 ,judd for areas in ,hungary and in the ,inner ,hebrides4 ,the features displayed in thin sections under the microscope were used by ,judd1 in a series of papers1 to substantiate his views2 but in ,france and ,germany these features became the source of subtle distinctions between the igneous rocks of ,cainozoic and pre-,cainozoic days4 ,the lavas1 in which some glassy matter could be traced1 were said to be typically post-,cretaceous1 and essentially different from those earlier types in which glass was replaced by finely crystalline matter2 while the coarsely crystalline igneous rocks were uniformly regarded as pre-,cainozoic4 ,glassy rocks1 such as pitchstone1 interbedded contemporaneously in ,permian or ,devonian strata1 were described as vitreous porphyries1 while those known to be of post-,cretaceous date might be styled andesites1 trachytes1 or rhyolites4 ,luckily common sense has recently triumphed in this matter1 and the relative scarcity of glassy types of igneous rocks in early geological formations has been recognised as due to the readiness with which glass undergoes secondary crystallisation4 ,the discussion has ended by showing that we have no evidence of world-wide changes in the types of material erupted during geological time4 ,at the present day1 attention has been focused on the processes that go on in subterranean cauldrons1 in the hope of explaining the differences between one type of extruded rock and another4 ,doctrines of descent have been elaborated1 and one of the most subtle systems of classification#ei has been based upon characters that the igneous rock might have possessed1 had circumstances not imparted others to it during the process of consolidation4 ,the principle of this classification is1 however1 obviously correct1 if we wish to trace back a rock bearing certain characters at the present day to the molten source from which it came4 ,,characters ,,of ,,igneous ,,rocks ,the characters of igneous rocks vary considerably according as they have consolidated under atmospheric pressure only1 or under that of superincumbent rocks4 ,we must remember also that submarine lavas have to sustain a pressure of an extra atmosphere for every thirty feet of depth1 or #djj atmospheres at #bjjj fathoms1 and that such rocks have a claim to be regarded as deep-seated4 ,the gases that igneous rocks contain1 probably as essential features of the molten magma1 and at a temperature above their critical points1 escape to a large extent near or at the surface of the earth4 ,the bubbles raised in lava1 whereby it is rendered scoriaceous1 and the clouds of vapour rising from cooling lava-flows and from the throat of a volcano in eruption1 are sufficient evidences of this process4 ,the extremely liquid lavas of ,kilauea in ,hawaii1 which emit very little vapour1 are notable as exceptions4 ,in the case of masses that cool underground1 the retention of gases1 and ultimately of liquids1 until a very late stage of consolidation retards crystallisation until temperatures are reached lower than those at which it starts in surface-flows4 ,as ,a4 ,harker points out#fj1 the loss of these substances1 by raising the melting-points in the magma1 may be the immediate cause of crystallisation1 quite as much as any actual cooling4 ,the formation of crystals in lavas is rapid1 and the average crystals are therefore small1 and often felted together in a mesh1 the interstices of which are filled by residual glass4 ,slowness of cooling is the really important factor that affects the size of crystals1 that is1 the coarseness of grain1 in igneous rocks4 ,pressure may promote crystallisation1 by raising the melting-points of minerals2 but1 after a certain maximum effect in this direction1 it is quite possible that an increase of pressure may actually lower the melting-points1 and cause one or other mineral to remain in solution in the magma4 ,it is not clear how pressure can affect the size of any constituent1 except by bringing about conditions under which it can go on growing1 while other constituents remain in solution1 or do not grow so fast4 ,such conditions may arise from the aid given by pressure to the retention of what ,french geologists have called agents minralisateurs4 ,several familiar minerals1 for instance albite1 orthoclase1 and quartz1 require the presence of water for their formation4 ,volatile substances1 not utilised in the ultimate product1 no doubt similarly assist the formation of many rock-forming minerals4 ,occasionally1 moreover1 as in the development of the micas and certain of the silicates known as zeolites1 some proportion of hydrogen is retained by minerals thus crystallising from the magma4 ,micas appear to require the presence of fluorine for their development4 ,j4 ,p4 ,iddings#fa1 however1 lays stress in this case on the chemical activity of hydrogen at high temperatures4 ,igneous rocks1 unless cooled with singular rapidity1 thus contain crystals of various kinds4 ,in lavas1 these may form the globular aggregates known as spherulites#fb1 or may accumulate as a compact ground of minute grains and needles1 not quite resolvable with the microscope4 ,in many rocks of slightly coarser grain1 a compact lithoidal or stony texture is set up1 which the microscope resolves into an aggregate of crystalline rods or granules4 ,such compact rocks are often styled felsitic4 ,in other types1 as in ordinary granite1 the constituent minerals are easily distinguished with the naked eye4 ,the order in which these constituents have developed is sometimes clear from the inclusion of one mineral in another4 ,when two substances are dissolved in one another1 there is a certain proportion between them1 varying with the substances1 which allows them to crystallise at the same time1 instead of in succession4 ,this eutectic proportion1 when attained by two mineral substances in a magma1 brings about a complete interlocking of their crystals1 as is seen in the quartz and alkali-felspar of the rock known as graphic granite4 ,the order of crystallisation of minerals from an ordinary non-eutectic magma is profoundly affected by the proportions in which their constituents are present in the mass4 ,the minerals1 when they have separated out1 are found to be mostly silicates4 ,a few oxides1 such as rutile1 magnetite1 and ilmenite1 may occur1 the two latter being especially common where iron is an important constituent of the rock4 ,but almost all igneous rocks consist largely of one or more species of felspar1 silica being here combined with alumina1 potash1 soda1 and lime4 ,free silica may remain1 and separates as quartz1 or rarely as tridymite4 ,pale mica occurs in many rocks of deep-seated origin4 ,in contrast with these light-coloured minerals1 iron1 magnesium1 and part of the calcium1 appear in another series of silicates1 usually dark in colour1 and this series may be broadly styled ferromagnesian4 ,the pyroxenes1 of which augite is the type1 the amphiboles1 of which hornblende is the type1 dark mica 7mostly biotite71 and olivine1 are the ordinary ferromagnesian minerals4 ,broadly1 then1 igneous rocks divide themselves by texture into 7i7 those which are completely crystalline1 and in which the minerals are distinctly visible2 7ii7 those which are completely crystalline1 but in which the crystals are so small as to give rise to a compact lithoidal ground-mass2 and 7iii7 those in which some glass is present4 ,the third group may appear lithoidal1 or in other cases actually glassy1 to the unaided eye4 ,this mode of division is justified from a natural history point of view4 ,the first group includes rocks that have consolidated slowly underground4 ,the second includes rocks cooled more quickly1 on the margins of magma-basins1 or as offshoots from them1 filling cracks in the surrounding rocks1 and producing wall-like masses known as dykes4 ,the third group appears mostly in dykes and lava-flows4 ,where a dyke has intruded among heated rocks and undergoes no sudden chilling1 it may become coarsely crystalline1 even though comparatively small4 ,some dykes exhibit a chilled margin of glass along their bounding surfaces1 and are none the less completely crystalline at the centre1 where cooling has been slow4 ,no structure is peculiar to dyke-rocks1 nor can a class be established for such rocks on chemical or mineralogical grounds1 even though a few special types of igneous rock may at present be known only among these minor intrusive bodies4 ,illustration3 ,fig4 #ad4 ,side of a ,volcanic ,cone4 ,ash-layer of #aijf on the west flank of ,vesuvius4 ,cliffs of the exploded crater of ,monte ,somma behind4 ,the fine-grained layers of volcanic dust1 commonly spoken of as ash1 and the coarser tuffs1 in which lumps of scoriaceous lava are clearly visible1 bridge the gap between sedimentary and igneous rocks4 ,the dust1 during a great eruption1 is distributed by wind over hundreds of square miles of country4 ,the tuffs1 deposited nearer the orifice of the volcano1 vary in coarseness from day to day1 and exhibit marked stratification4 ,ash-beds and tuffs may be laid out in lakes or in the sea1 and their layers may then include organic remains4 ,waves may round their particles on the shore1 and may sift them till only a coarse volcanic sand remains4 ,after an eruption1 the newly deposited ash and tuff usually form obvious layers on the surface of the country4 ,landslips on the side of the volcanic cone may reveal sections of the new coating and of previously stratified material 7,fig4 #ad74 ,in certain districts1 sedimentary and other rocks torn off from below form a large part of the fragmental deposits of volcanic action4 ,the characteristic volcanic cone is itself due to the greater accumulation of tuffs and ashes near the vent 7,fig4 #ae74 ,the loose tuffs formed of scori allow water to percolate easily through them1 and a cone of fairly coarse material resists the weather well4 ,the remarkable freshness of the extinct cinder-cones of ,auvergne was thus long ago explained by ,lyell4 ,surfaces of ash1 on the other hand1 are easily washed down by rain in the form of dangerous mud-flows1 which spread across the lowlands1 and give rise to compact clays1 shrinking as they dry4 ,illustration3 ,fig4 #ae4 ,tuff-,cone with ,tuff-,beds at the base4 ,puy de la ,vache1 ,puy-de-,dme1 ,france4 ,lava-flows are masses of molten rock that have welled out from the vent1 without being torn to pieces by the explosion of the gases that they contained4 ,the rapidity of their flow depends on their chemical composition1 on the amount of gases present1 and on the temperature at which they are extruded4 ,the more highly siliceous lavas1 for a given temperature1 are more viscous than those towards the basaltic end of the series1 which contain only about #dh per cent4 of silica4 ,a lava of considerable fluidity will consolidate in somewhat thin sheets with smooth and ropy surfaces4 ,a less fluid type will become markedly scoriaceous1 where the vapours endeavour to escape from it2 the rugged crust formed on its upper cooling surface will be broken up by the continued movement of the more liquid mass below1 and the blocks thus formed may become rolled over the advancing front of the flow and entombed in the portion that has not yet consolidated4 ,the surface of ordinary lava-flows remains rough for centuries1 and only slowly crumbles down before weathering to form a soil4 ,while tuff-beds provide light and fertile lands1 the lava-streams remain marked out among them1 as sinuous bands of rock1 given over to an irregular growth of woodland4 ,by repeated outflows1 lavas tend to fill up the interspaces between the earlier streams1 just as these have filled up the hollows in the country over which they spread4 ,a uniform surface thus arises1 and lava-plains eventually bury a varied land of hill and dale4 ,where a number of small vents have opened1 perhaps along parallel fissures in the earth1 the flooding of the country with igneous rock may lead to an appearance of stratification in masses extending over hundreds of square miles4 ,sections in the igneous series1 however1 show that the individual flows dove-tail into and overlap one another1 more rapidly than is the case with the lenticular masses that constitute an ordinary sedimentary series4 ,after the constituents of the lava have begun to crystallise1 and when the rock may be considered solid1 cracks due to contraction are set up4 ,the upper part of the flow1 radiating its heat and parting with its gases into the air above1 solidifies comparatively rapidly1 and cracks arise without much regularity4 ,now and then1 columnar structure1 like that of dried starch1 appears on a small scale1 the columns starting from various oblique surfaces of cooling1 and lying in consequence in various directions in the rock4 ,j4 ,p4 ,iddings shows that curvature of the columns will result if one portion of the surface loses heat more rapidly than another4 ,as the contraction-cracks bounding the columns spread inwards1 the layer reached by them at any time in the lava will be farther in from a part of the surface where cooling is rapid than it will be from a part where it is slow4 ,hence the layer in the lava where contractional stresses are producing cracks1 i4e4 the layer reached at any time by the inner ends of the contraction-columns1 will be a curved one1 and its curvature will increase as it occupies positions more and more removed from the surface of the lava-flow4 ,the axes of the contraction-columns1 as they spread1 are perpendicular to this layer1 and the columns will thus curve as their development proceeds4 ,the base of a massive lava-flow1 however1 cools under much more uniform conditions1 and the columns1 stretching upwards from the ground and produced by slow contraction1 give rise to the regular prismatic structures long ago known as giants' causeways4 ,the original ,giant's ,causeway in the county of ,antrim is the lower part of a basaltic flow1 exposed by denudation on the shore4 ,fingal's ,cave in ,staffa owes its tough compact roof to the preservation of that portion of the flow which cooled downwards from the upper surface4 ,g4 ,p4 ,scrope#fc long ago observed this dual structure in columnar lavas4 ,the columns1 or the more irregular joint-blocks that sometimes represent them1 are often subdivided by further contraction into spheroids1 the coats of which peel off1 as the rock weathers1 like those of an onion4 ,the curved cross-joints of massive columns1 now convex upwards1 now concave1 represent the same tendency towards globular contraction4 ,a lava-flow is sometimes divided into large rudely spheroidal masses1 which fit into one another1 and which show signs of more rapid cooling on their surfaces4 ,these were particularly observed on the mountains near ,mont ,genvre by ,cole and ,gregory#fd1 who compared the forms to pillows or soft cushions pressed upon and against one another4 ,it was suggested that these forms were produced by the seething of viscid lavas1 masses being heaved up and falling over1 and the outer layers having time to cool in a glassy state before they were deformed by contact with others4 ,this pillow-structure has been widely recognised1 and ,j4 ,j4 ,h4 ,teall has remarked how often pillow-lavas are associated with radiolarian cherts4 ,he regarded them1 therefore1 as of submarine origin4 ,sir ,a4 ,geikie#fe1 moreover1 stated that the spheroidal sack-like structure was produced by the flow of such lavas into water or watery silt4 ,this acute suggestion has now been verified by ,tempest ,anderson#ff1 who has observed in ,samoa the chilling of the lobes of lava1 as they are thrust off into the sea and washed over by the waves4 ,h4 ,dewey and ,j4 ,s4 ,flett#fg have pointed out that pillow-structure commonly occurs in lavas in which there has been a conversion of lime soda felspars into albite1 a change frequent in a series of rocks which they call the spilitic suite4 ,the importation of soda is attributed to vapours entering soon after the consolidation of the rock1 and it is urged that any excess of sodium silicate must have escaped into the sea-water in which the pillow-lavas were produced4 ,hence radiolaria will flourish in the neighbourhood 7presuming that a decomposition of the silicate can be brought about71 and their remains will in time form flint in the hollows of the lavas4 ,the paper quoted contains numerous references to previous work1 and is a suggestive example of how petrographic study may go hand in hand with the appreciation of rocks from a natural history point of view4 ,it is only characteristic of the subject of petrology that ,g4 ,steinmann#fh has with equal ingenuity explained the relations between radiolaria and spilitic lavas by reminding us that gravity-determinations show an excess of basic material under the oceans and of lighter material1 rich in silica1 under continental land4 ,hence1 when deep-sea deposits are crumpled by earth-movements1 basic types of rock1 graduating even into serpentine1 become associated with radiolarian chert1 partly as extruded lavas1 but usually as intrusive sheets injected at the epoch of mountain-building4 ,the characters of igneous rocks in dykes1 that is1 of those types that have consolidated in fissures1 resemble in many respects the characters of lava-flows4 ,chilling being usually equal on both surfaces1 glassy or compact types of rock occur on both sides1 and the dyke is1 as previously observed1 more crystalline in the centre4 ,columnar structures arise from both surfaces1 the dyke also shrinking parallel to its margins4 ,in the outer layers so formed1 the columns are small1 and they increase in diameter nearer the centre4 ,in small dykes and veins1 the columns may run continuously from side to side2 in larger ones1 they meet along a central surface1 which forms1 on weathering1 a plane of weakness in the rock4 ,dykes may thus become worn away1 decay spreading from the central region1 and leaving the more resisting and more glassy portions clinging to the bounding walls4 ,where1 however1 the surrounding rocks are more easily worn away than the igneous invader1 as very often happens1 the dykes stand out on the surface as great ribs and walls4 ,the rocks cooled in the deep-seated cauldrons1 under what are styled plutonic conditions1 have parted with their gases so slowly that they do not show scoriaceous structure4 ,they may become very coarsely crystalline1 like many of the ,scandinavian granites2 minerals1 moreover1 may be produced which are unstable or difficult to form nearer the surface4 ,crystals developed in plutonic surroundings become carried forward when the partially consolidated mass is pressed up to a volcanic orifice1 and may undergo resorption on the way4 ,many1 however1 escape1 and impart a porphyritic structure to lavas4 ,the deep-seated rock1 from causes that promote the growth of one mineral and the retention of another in solution1 may also become porphyritic in situ1 smaller crystals1 or even a eutectic intergrowth1 finally filling in the ground4 ,the viscidity of igneous rocks may cause any of the types to show a fluidal structure4 ,constituents already formed become dragged along in parallel series as the mass moves forward4 ,sometimes a group of spherulites1 or a knot of felsitic matter caused by the dense growth of embryo-crystals1 is stretched out into a sheet1 and on fractured surfaces a banded structure characterises the mass4 ,these banded rocks record1 in their crumpled and obviously fluidal layers1 the formerly molten condition of the mass4 ,even completely crystalline rocks may show parallel arrangement of their minerals1 owing to flow during the last stages of consolidation1 or to pressure from the walls of the cauldron1 influencing the positions taken up by crystals that possess a rod-like or platy form4 ,illustration3 ,fig4 #af4 ,granite invading ,mica-,schist4 ,clifton1 near ,cape ,town4 ,adjacent sections were studied by ,charles ,darwin 7see p4 #aef74 ,the conspicuously banded structures in some crystalline rocks that are often grouped with the metamorphic gneisses may1 however1 be best explained by their composite origin1 and the history of the structure is easily determinable in the field4 ,a common case arises where a granite magma1 perhaps already bearing crystals1 is intruded1 under pressure operating from a distance1 into a well-bedded series of sedimentary rocks4 ,the sediments open up like the leaves of a book and admit the invader along their planes of stratification4 ,even limestone may thus become interlaminated with an igneous rock1 just as basalt has been known to separate the annual rings of trees involved in it4 ,this intimate admixture permits of extensive mineral changes1 and the two types of rock1 probably very different in geological age1 become welded together into a composite gneiss1 both members of which have influenced one another by contact-metamorphism1 often across a wide stretch of country 7,fig4 #af74 ,intrusive igneous rocks in the field will1 however1 ordinarily prove their character by cutting somewhere across the prevalent structure of the district4 ,when the materials that elsewhere form dykes penetrate between strata for considerable distances as intrusive sheets1 they may yet be traced to some point where they have made use of a crack across the bedding4 ,the necks or plugs of old volcanic centres sometimes seem to occupy orifices drilled1 or rather shattered1 by explosion right through the overlying obstacles4 ,the approximately circular necks in ,south ,africa1 filled by brecciated masses of serpentinous rock1 are notable examples4 ,the underground cauldrons themselves1 when brought to light by denudation1 are represented by regions of crystalline rock1 which may have various relations to their surroundings4 ,we may trace1 in every case1 upon their margins the ramifying veins that first proved to ,james ,hutton that granite was younger than the rocks among which it lay4 ,but the portion exposed may be merely the top of a huge body or batholite of igneous matter1 stretching far down into the crust2 or it may be part of a localised knot1 which filled up some cavity provided for it by earth-movement1 oozing in step by step as room was made for its advance4 ,in the latter case1 it was originally bounded above by some series of strata which was arched up as a dome or as an anticline4 ,or possibly strata have been moved apart from one another1 the upper ones sliding over the lower ones and at the same time bulging upwards1 so as to leave a cavity of roughly hemispherical form4 ,such a space1 allowing relief from pressure1 will be occupied by igneous rock1 which may or may not have a direct root through the stratum underneath it4 ,the igneous mass may in such cases be merely an expansion of a large intrusive sheet4 ,it sends off veins into the roof above1 and can only be distinguished from a batholite by the presence of stratified rock beneath it4 ,occurrences of this kind were first described in the ,henry ,mountains of ,utah by ,g4 ,k4 ,gilbert1 who gave them the name of stone-cisterns or laccoliths1 a word now commonly written laccolites4 ,it may be questioned if the expansion of the gases in the intruding igneous rock is sufficient in itself to form the laccolitic dome4 ,the igneous rock has probably been pressed into position by the forces that produced the earth-movements4 ,in many cases1 batholites seem to have worked their way upwards without any relation to earth-movements in the district4 ,the processes by which they come into place among other rocks are worthy of separate consideration4 ,,the ,,intrusion ,,of ,,large ,,bodies ,,of ,,igneous ,,rock ,attention has been already called to the composite gneisses formed by the intrusion of an igneous magma between the leaves1 as it were1 of sediments4 ,such occurrences are often seen on the margins of batholites or of any kind of igneous dome1 and they no doubt represent the picking off of layer after layer from the walls surrounding the intrusive mass4 ,if these layers can become absorbed into the igneous rock1 the crest of the dome can advance1 and the dome itself can widen1 so long as sufficient heat is supplied to it from below4 ,space is found for the intrusive mass at the expense of the marginal rocks2 but it is obvious that the portions absorbed merely add to the bulk of the igneous material4 ,the composition of the latter must also undergo modification4 ,its great size1 reaching as it does far down into the crust1 in comparison with the quantity of matter absorbed in the upper regions1 may render such modification very difficult to trace beyond the latest zone of contact4 ,petrologists differ very widely as to the extent to which igneous masses assume their place in the upper regions of the crust by processes of stoping1 absorption1 and assimilation4 ,the statement1 however1 in a recent work that the assimilation hypothesis is still supported by some ,french geologists is calculated to surprise those who recognise the trend of modern opinion both in ,america and on the continent of ,europe4 ,far from the views of ,a4 ,michel ,lvy1 ,c4 ,barrois1 and ,a4 ,lacroix1 surviving as an expression of national perversity1 they have been supported to a remarkable degree by the observations of ,sederholm in ,finland1 of ,lepsius and ,h4 ,credner in ,saxony1 of ,a4 ,lawson and ,f4 ,d4 ,adams in ,north ,america1 and by the careful reasoning of ,c4 ,doelter#fi based largely on his own experimental work4 ,a4 ,harker#gj and ,j4 ,p4 ,iddings#ga have argued that assimilation is merely a local phenomenon1 of little importance in the theory of igneous intrusion4 ,w4 ,c4 ,brgger#gb1 however1 who strongly supports the laccolitic view for the ,christiania district1 expresses himself with far more caution1 and leaves the way clear for conclusions as to absorption and mingling of molten products in the lower regions of the crust4 ,doelter lays stress on the influence of high temperature1 and especially of the highly heated gases in the igneous rock1 in promoting corrosion of the cauldron-walls4 ,he attributes greater power of corrosion to the magmas rich in silica1 and agrees with ,r4 ,a4 ,daly that the rapidly moving basic magmas reach the upper layers of the crust in a condition of comparative purity4 ,daly#gc may be looked on as an extremist in this matter2 but it is hard for those who have studied regions where the deep-seated cauldrons have been cut across by denudation to avoid very large views of igneous absorption4 ,the contact-zones between the igneous mass and the surrounding rocks are often seen merely in cross-section on the flanks of a batholite or laccolite4 ,in the areas of ,archan rocks1 on the other hand1 where prolonged denudation has exposed the zones of repeated interaction over hundreds of square miles on an approximately horizontal surface1 one may form some idea of the processes that are still effective in the depths4 ,g4 ,v4 ,hawes#gd1 in #ahha1 recognised the importance of the process known by the mining term of stoping1 as a means whereby igneous rocks work their way upward in the crust4 ,cracks in the overlying roof are entered by the magma1 blocks are wedged off1 and these are ultimately absorbed in the molten mass4 ,in this matter ,hawes stands as a pioneer4 ,as the viscosity of the magma increases during cooling1 the blocks last detached may remain embedded in the marginal zone4 ,the remarkable purity of this zone1 however1 in many cases has raised an obvious difficulty2 but it has been pointed out#ge that the modified marginal and composite rock may continuously sink down into the depths1 aided by any of the causes that promote magmatic differentiation1 while a fairly pure magma1 almost of the original composition1 is left on the crest of the advancing dome4 ,r4 ,a4 ,daly#gf has developed the stoping theory with considerable boldness4 ,the areas most likely to carry conviction to those who doubt that igneous masses can be intruded at the expense of their surroundings are those where banded gneisses have arisen on a regional scale 7see p4 #afj74 ,,the ,,range ,,of ,,composition ,,in ,,igneous ,,rocks ,the broad division of igneous rocks into those of light colour and of low specific gravity on the one hand and those that are dark and heavy on the other is a very natural one1 and ,bunsen and ,durocher insisted that two magmas were fundamental in the crust4 ,in one of these1 the acid magma1 which gives rise to granites and rhyolites1 silica formed about #gj per cent4 by weight of the ultimate rocks2 in the other1 it formed about #ej per cent41 and the products are basic diorites1 gabbros1 and basalts#gg4 ,the former group of rocks is rich in alkalies1 the latter1 the basic group1 in calcium1 magnesium1 and iron4 ,the mixture of these more extreme types of magma was held to give rise to what are now called intermediate rocks4 ,two other views are of course possible4 ,if the composition of the globe was originally uniform1 the two magmas must have arisen by separation from one of intermediate nature4 ,hence1 in any cauldron in the crust1 in place of one of two magmas1 an intermediate magma may be presumed to exist1 and to split up1 from various causes1 into a number of parts which are separately erupted at the surface4 ,charles ,darwin's#gh remarks as to the sinking of crystals in a cooling magma1 and the consequent production of a trachytic and basaltic type in the same cauldron1 led the way to a general acceptance of the theory of magmatic differentiation in laccolites and batholites4 ,w4 ,c4 ,brgger's#gi brilliant explanation of the variation and succession of types of igneous rock in the ,christiania district has had a profound influence on workers in other fields1 and has perhaps directed attention away from the parallel possibilities of differentiation by assimilation4 ,the assimilation theory provides the second possible view above referred to4 ,a magma may be modified by the rocks into which it intrudes1 so that a basic fluid may become charged with silica from a sandstone1 the product crystallising as a granite2 while an acid fluid may become so charged with limestone that diorite ultimately results4 ,a4 ,harker#hj has discussed both theories clearly1 with a strong leaning to the acceptance of magmatic differentiation in the cauldron as the only important cause of variation4 ,r4 ,a4 ,daly1 on the other hand1 goes at least as far as ,lacroix in ,france in supporting the theory of assimilation4 ,for him1 the primitive igneous magma is already basic1 and basalts are therefore the prevalent type of igneous rock4 ,they reach us1 moreover1 from considerable depths4 ,the acid rocks are formed by amalgamation of this magma with siliceous material lying nearer the earth's surface4 ,igneous rocks exceptionally rich in alkalies1 the so-called alkaline series1 result from the absorption of limestone in the magma2 denser lime-bearing silicates are thus formed1 which sink by gravitation1 leaving a lighter magma above in which soda has become concentrated4 ,carbon dioxide liberated from the limestone also plays a part in carrying up the alkalies that might otherwise remain in a lower portion#ha4 ,e4 ,h4 ,l4 ,schwarz#hb extends ,daly's views with an almost romantic fulness4 ,he holds1 with ,chamberlin1 that the primitive globe resulted from the aggregation of basic meteoritic material4 ,the more siliceous crust arose from the withdrawal of magnesium and iron into the depths by long-continued processes of leaching and gravitation4 ,the melting of this crust produces the acid igneous rocks4 ,igneous cauldrons originate in the heat due to faulting1 or to crumpling1 or even to the impact of gigantic meteorites4 ,when a molten magma is locally established1 variation occurs in it by assimilation of different types of material round it4 ,the balance of judgment as to differentiation and assimilation1 which should be regarded as parallel probabilities rather than as rival propositions1 is admirably held by ,c4 ,doelter#hc1 whose chapters on this matter can be appreciated by all geologists4 ,it is of course possible that differentiation of type1 from various causes1 has already proceeded so far in the earth's crust as to produce noteworthy contrasts in the rocks erupted in different areas4 ,the interior of our globe1 on ,chamberlin's planetesimal hypothesis1 need not have been uniform in constitution1 either at the outset or at any subsequent time4 ,j4 ,w4 ,judd#hd has called attention to the existence of petrographical provinces1 a conception that has been very fruitful in results4 ,these provinces have been grouped by ,harker#he in two branches1 characterised respectively by rocks rich in alkalies and by rocks rich in lime4 ,the former branch appears to be associated with the movements of faulting and block-structure1 rather than of crumpling1 that have produced ,e4 ,suess's ,atlantic type of coast4 ,the rocks rich in lime1 on the other hand1 are said to be characteristic of areas that have been folded like the countries bordering the ,pacific4 ,the names ,atlantic and ,pacific have consequently been given to the two branches1 but these terms seem too geographical in their suggestion4 ,dewey and ,flett#hf have put forward a third type of magma1 giving rise especially to albite as a primary or secondary constituent1 and characterised by the production of pillow-lavas4 ,this type is held to be associated with areas that have steadily subsided1 without much folding4 ,g4 ,steinmann#hg1 however1 has connected the spilites and ophiolitic rocks with regions of intense over-folding4 ,so far1 there are many cases where it is difficult to assign a petrographic province to one or other of these branches1 and the system seems to demand more simplicity within the provinces than nature is prepared to yield4 ,whatever the causes of variation1 it is necessary to mark out by names certain kinds of igneous material1 and it is generally accepted that the types thus set up are best based on chemical composition4 ,at the same time1 the minerals present in the rock1 and also its structure1 record certain phases of its history1 and deserve an important place in any system of classification4 ,the natural history of an igneous rock is concerned with its mode of occurrence1 and no isolated specimen can satisfy the geological investigator4 ,in the field1 the porphyritic crystals1 which have an important influence on the total chemical composition1 may be found to be strangers to the magma1 and to have been derived from some mass imperfectly absorbed4 ,the dark flecks and patches in a granitoid rock1 so often ascribed1 somewhat mysteriously1 to local segregation in the magma1 again and again prove to be metamorphosed and minutely injected fragments of foreign rocks#hh4 ,none the less1 a broad classification is possible on chemical grounds1 and the acid1 intermediate1 basic1 and ultrabasic grouping adopted by ,judd has been found of great convenience4 ,among acid rocks we have granite as the coarsely crystalline type1 with potassium felspars prevalent and the excess of silica manifest as quartz4 ,the finer grained and sometimes compact types are the eurites1 quartz-felsites1 or quartz-porphyries4 ,when the rock contains more or less residual glass1 we have what are now known as rhyolites1 of which ordinary obsidian is the most glassy representative4 ,the opposite types1 those of the basic group1 include1 at the coarsely crystalline end1 gabbro and basic diorite2 the finely crystalline forms are styled dolerites1 and those with a trace of glass1 or at any rate very fine-grained and compact1 are basalts4 ,glassy types are naturally rare in this group1 owing to the unsuitable chemical composition4 ,between granite and gabbro lie various rocks of intermediate composition1 some of them rich in soda rather than in potash4 ,syenite1 granodiorite1 and the diorites with a prevalence of soda over lime1 are coarsely crystalline types4 ,compact types of these of course occur4 ,it will be sufficient1 however1 here to name the forms with traces of residual glass1 which range from trachyte1 the type rich in potash1 to andesite1 which connects them with basalt1 in a series where lime ultimately predominates over soda4 ,in the ultrabasic group are a number of exceptional types4 ,olivine often becomes an important constituent1 and the rocks then decompose into the soft green or reddish masses known as serpentine--or1 more properly1 serpentine-rock4 ,igneous rocks1 owing to their range of mineral composition and of structure1 combined with their general hardness1 lend themselves to various economic purposes4 ,while the granites1 resisting atmospheric attack admirably in a polished state1 provide our handsomest building-stones1 dolerites and fine-grained diorites1 which owe their toughness largely to the interlocked relations of their constituent minerals1 serve as our most satisfactory road-metals4 ,,the ,,scenery ,,of ,,igneous ,,rocks ,volcanic landscapes1 where activity is very recent or still in progress1 present a number of characteristic surface-forms4 ,the cones that have accumulated round the vents surpass all other hills in regularity of outline1 and the crater in the summit is often relatively large4 ,lava-cones may be steep-sided bosses when formed of protrusions of viscid rocks rich in silica1 like the remarkable domes in the north of ,bohemia1 or they may present very gentle slopes where fluid basic lavas have been extruded4 ,tuff-cones are liable to be breached on one side1 owing to the outflow of lava which the crater-wall could not sustain1 and they then assume the form of a mountain in which glacial influences have hollowed out a cirque4 ,rain washes down the loose materials from great volcanic cones1 and emphasises the concave curve of the mountain sides1 the form that is so beautiful in ,fuji-yama in ,japan1 and which ,hokusai1 with pardonable and affectionate exaggeration1 reproduced in a hundred illustrations4 ,ultimately1 however1 grooves appear on the flanks of the cone1 in which permanent streams gather1 and the slopes are dissected and worn away4 ,during this process1 the tuffs yield steep and fantastic forms1 and wall-like dykes weather out among them4 ,the dykes are usually the last features to decay4 ,where the vent has been plugged with lava at the close of its activity1 the neck of rock often remains standing above the surrounding country4 ,the site of cone after cone can be picked out in this way in the ,cainozoic volcanic areas of central ,germany4 ,the jutting crag of trachyte or of basalt has often been seized on as the site of a feudal castle1 under which the dependent agriculturists still gather at nightfall in their red-roofed town4 ,the group of sheer-sided necks in the ,hegau in southern ,wrttemberg1 the ,hohentwiel1 ,hohenkrhen1 and the rest1 form a very striking landscape amid undulating ,cainozoic lands4 ,the lava-beds that cover wide areas are naturally of basic composition4 ,basalts thus form enormous plains with rugged surfaces1 on which at last a red-brown soil collects4 ,when exposed to denudation from the edge of the region inwards1 they develop a marked terrace-structure1 through which the rivers cut steep and grim ravines4 ,grass may grow on the ledges and the tables2 but the scarps1 controlled by the well-marked vertical jointing of the lavas1 remain sharp and prominent1 and the rock falls away from these walls in whole columns at a time4 ,this structure is characteristically seen in northern ,mull and the adjacent smaller isles1 and is still more impressive from the centre to the north of ,skye1 where the rain swept terraces covered by grass and bog and scanty oatfields1 and the black steps of rock between them1 present a scene of strange monotony and desolation4 ,in regions less exposed to stormy weather1 the lava-plateaus may provide good soils4 ,for instance1 after the great seaward scarp of the basalts has been crossed in the counties of ,antrim and of ,londonderry1 the lava-fields1 dropped by faults towards ,lough ,neagh1 are seen to be occupied by prosperous farms4 ,in arid countries1 however1 the savage surface of the flows merely becomes modified by red dust and scoriaceous gravel1 worn by wind and changes of temperature from the upstanding portions of the land4 ,where a stratified country has been freely invaded by sheets of lava along its planes of bedding1 the stratification is emphasised in any part exposed to weathering4 ,the resisting igneous rock stands out in scarps along the hills1 and marks out any folds that have been formed since the epoch of its intrusion4 ,when the beds remain fairly level1 and are also uplifted1 flat-topped hills are formed by the intrusive sheets1 like those that may be carved out of a country flooded over by lava-streams4 ,the crystalline rock1 very probably a dolerite1 protects what lies below it4 ,the kopjes north of the ,great ,karroo in the centre of the ,cape of ,good ,hope are thus level on the crest and bounded by a steep wall or krans of rock4 ,the edges of similar sills of igneous rock have controlled much of the scenery between the ,highland border of ,scotland and the ,tyne4 ,a fine example is the indented scarp of the ,great ,whin ,sill1 a sheet of dolerite intruded among the ,carboniferous strata of ,northumberland4 ,this mass forms a platform for ,bamburgh ,castle against the wild ,north ,sea1 and is traceable south-westward across the country towards ,carlisle4 ,north of ,hexham1 its escarpment is occupied by ,hadrian's wall1 and the town of ,borcovicus was planted on the edge1 overlooking all ,northumbria4 ,the farmers of ,north ,britain and ,ireland have long known upstanding igneous dykes as unprofitable whinstones4 ,the regularity of direction among dykes over very wide areas points to their intrusion along cracks produced by stretching of the crust4 ,radial grouping of dykes1 such as one finds near volcanic necks1 or1 on a gigantic scale1 round ,tycho on the moon1 may be due to explosive action2 but the majority of dykes seem to have followed upon earth-movement4 ,in the north of ,ireland1 from the coast of ,down to that of ,donegal1 a series of compact rocks of ,devonian age occurs in dykes lying almost invariably north and south4 ,the post-,cretaceous dykes of the same region have a still more uniform trend1 from north-west to south-east4 ,such series of dykes modify the scenery of coasts by forming promontories and serviceable piers for boats4 ,the offshoots near the surface of a great intrusive mass are far less regular4 ,we are here close to the zone of attack1 the shatter-zone1 and the structures or regular fracture-planes of the overlying rock only partially control the position taken up by the intrusive magma4 ,irregular knots and bosses appear in place of far-spreading sheets1 and a network of crossing veins occurs1 instead of a system of coordinated dykes4 ,the resulting country is hummocky and broken1 and1 where the cauldron itself has become exposed1 striking contrasts of surface are seen as we pass from the igneous core to the older and frequently stratified rocks upon its flanks4 ,some large bodies of intrusive rock have1 however1 been formed sheet by sheet1 and a bedded sill-like structure is then revealed in them on weathering4 ,sir ,a4 ,geikie#hi calls attention to this in his description of the heart of the black gabbro mass in ,skye4 ,but1 as a rule1 the continuity of structure in batholites1 and their characteristic joint-planes set at angles to one another1 cause them to appear as massive blocks in the landscape1 untraversed by any regular lines4 ,granite1 with its broad tabular jointing1 which is often developed parallel to a surface of cooling1 forms rounded slopes and domes after long-continued weathering4 ,when reared high into the zone of frost-action1 it develops spires and pinnacles1 as in the huge aiguilles of ,mont ,blanc4 ,but1 as decay goes on1 the uniform descent of boulders and sand forms spreading taluses1 banked against the lower slopes1 while the curving joints1 not too closely set1 promote a smoothness on the higher lands4 ,these joints1 moreover1 divide the rock into boulders almost ready-made4 ,tabular structure sometimes predominates2 but even in this case the exposed ends of the layers soon become rounded1 as the felspar crystals pass into a powdery state4 ,commonly1 a rough spheroidal structure prevails1 as may be traced in many of the ,dartmoor tors1 and the blocks that slip away through widening of the joints become more and more rounded as their surfaces crumble on the talus 7,fig4 #ag74 ,illustration3 ,fig4 #ag4 ,weathering ,granite4 ,lundy ,island4 ,in tropical lands1 granite exfoliates under the alternations of clear hot days and clear cold nights1 and the joint-structure allows of the formation of great round-backed surfaces1 on which spheroidal boulders appear poised4 ,these boulders are the relics of an overlying layer of granite1 most of which has slipped away to the hill-foot4 ,their surfaces crumble1 owing to the unequal expansion of the constituent minerals4 ,when the rainy season sets in1 the decomposed crust is washed away2 during the dry season it falls off in flakes and powder4 ,in this way the magnificent series of monoliths that surround the grave of ,cecil ,rhodes in the ,matopo ,hills have become separated out from a continuous sheet of granite4 ,they stand now like glacial boulders on a surface almost as smooth as that of a roche moutonne 7,fig4 #ah74 ,the landscape for miles around is fantastic with huge fallen masses1 and with high-perched blocks that seem about to fall4 ,similar scenery is well known in central ,india1 and exfoliation controls the form of mountain-domes in ,california and ,brazil4 ,j4 ,c4 ,branner#ij lays most stress on temperature-changes in the surface-zone1 and little on original spheroidal jointing1 in promoting the exfoliation of the rounded boulders4 ,illustration3 ,fig4 #ah4 ,granite weathering under tropical conditions4 ,rhodes's ,grave1 ,matopo ,hills1 ,s4 ,rhodesia4 ,the blocks like boulders are residues of a sheet of granite that once overlay the hill4 ,the basic rocks present far more rugged outlines4 ,when a cauldron occupied by basic diorite or by gabbro comes under denuding action1 the numerous crossing joints oppose the formation of domes or tables4 ,the weather widens one groove here1 another there2 the rock breaks away in angular fragments rather than as a powder over a broad surface1 and serrated edges and jagged pinnacles arise along the crests4 ,the diorites among our old metamorphic rocks in ,scotland or in ,ireland can be recognised on the sky-line at considerable distances4 ,sir ,a4 ,geikie1 in his ,scenery of ,scotland1 has made the contrast between granite and gabbro in the centre of the ,isle of ,skye familiar to all geologists4 ,here the two types of rock were erupted at no long interval1 and they have been exposed to denudation under the same conditions4 ,j4 ,macculloch dwelt in #ahaiia on the relative resistance of the gabbro and the rapid disintegration of the granite hills1 quaintly remarking of the latter that the loose stones1 by their constant descent from the summits1 obscure the rocky surface1 covering the sides with long torrents of red rubbish even more unpleasing to the sight than their conoidal forms4 ,macculloch noted that the loose blocks in the gabbro region lay much as they had fallen1 without the production of a sand4 ,in most mountain-chains produced by folding1 igneous matter has been forced up as an accompaniment of the earth-movements4 ,the local knots and laccolites1 or the great cores admitted along certain anticlines1 stand out on weathering among schistose or stratified hills4 ,their surfaces are marked by accidents1 and each peak as it comes into view offers something of a new surprise4 ,the wall of ,mont ,blanc from the angle near ,entrves1 and the huge crag of the ,matterhorn above the valley of the ,visp1 have illustrated to every traveller the dominance of igneous masses in the landscape4 ,in our own islands1 the granites of ,ben ,cruachan and ,cairn ,gorm have resisted long ages of denudation2 an intrusive sheet of finer grain forms the long sheer wall of ,cader ,idris2 while obsidian lava-flows1 now grey and dull and crystalline1 have furnished on ,snowdon the finest scenery of ,wales4 ,the fortress-town of ,edinburgh has arisen on the relics of a dead volcano2 and the high moor of ,leinster1 so long the peril of the ,english1 records an igneous cauldron that has been exposed to denudation from the opening of ,devonian times4 ,,chapter ,,vi ,,metamorphic ,,rocks ,,introduction#ib ,under the term metamorphism1 considered philologically1 any change may be included that is undergone by rocks after their original deposition4 ,van ,hise1 in his monumental treatise1 covers processes of cementation and alteration by percolating waters1 as well as those larger changes that accompany earth-movement and the transference of rocks into regions of igneous activity4 ,it is1 indeed1 impossible to draw any just line in this matter2 but there is a general agreement that metamorphic rocks are those that have been altered by heat or pressure or both1 either on a local or a regional scale1 with the result that new structures1 or new minerals1 or both1 have arisen in the mass4 ,the efficacy of heat alone or of pressure alone1 of contact-metamorphism or of dynamo-metamorphism1 in producing considerable changes has been much debated4 ,some of the thermal changes have been already referred to in the chapter on igneous rocks4 ,while1 moreover1 the new structures and the development of mica in ordinary slate bring it into the metamorphic group1 we have found it convenient to describe the slates in connexion with common clays4 ,the rocks now to be dealt with give evidence of more extreme changes1 and the crystalline character of their constituents is appreciable by the unaided eye4 ,for the most part1 then1 this chapter treats of gneisses and schists4 ,the wider use of the terms schiste and schiefer on the continent of ,europe makes it necessary in most countries to style the metamorphic forms crystalline schists4 ,over wide areas of certain countries1 and sometimes when we approach the localised cores of mountain-chains1 the rocks show a parallel arrangement of their constituents1 reminding us of sediments2 but their constituents are all crystalline1 and they are more interlocked with one another than is the case in ordinary strata4 ,such rocks have long been said to be foliated4 ,the term was used by ,g4 ,p4 ,scrope as far back as #ahbe2 but this author1 in common with most geologists of his day1 regarded the mineral folia as resulting from sedimentation4 ,d',aubuisson de ,voisins#ic had already referred the parallelism of the feuillets of mica in schists to some cause acting on them during the consolidation of the rock from a plastic state2 but it was left for ,charles ,darwin#id1 in his remarkable observations on metamorphic rocks in #ahdf1 to separate clearly foliation from stratification4 ,in all cases of metamorphism1 we have to bear in mind that the alteration may be both chemical and physical4 ,substances may have been removed from the rock1 others may have been imported4 ,the crystalline constituents that are now present do not necessarily result from the crystallisation of the original materials of the rock4 ,,mica ,,and ,,hornblende ,,schists ,schists are the ordinary foliated rocks of fine or medium grain4 ,the folia are really flattened lenticular mineral aggregates1 often bent and waved1 lying on and against one another1 with their platy surfaces in parallel planes4 ,they result 7i7 from the deformation under pressure of objects already present in the rock1 such as pebbles or crystals2 or 7ii7 from the development of minerals under pressure during the process of metamorphism1 such minerals being allowed greater facilities for growth in directions perpendicular to that from which the pressure is exerted2 or 7iii7 from the development of minerals1 notably mica1 along the planes of weakness provided by stratification or by cleavage4 ,the trend of foliation-planes across a country is often1 as ,darwin pointed out1 remarkably regular2 in some cases1 it follows that of the stratification1 in others that of cleavage4 ,the wrinkling of the foliation must be ascribed to subsequent compression1 and all the features seen in the strain-slip structure of slate 7p4 #ib7 are repeated on a somewhat coarser scale in schists4 ,some schists are undoubtedly produced by the contact-metamorphism of shales4 ,on the flanks of mountain-chains1 where argillaceous rocks have been arched into domes1 and where granite has intruded as a core1 the complete passage can be traced from sediment to schist4 ,the clay-rocks lend themselves readily to the production of mica1 usually of the pale type4 ,andalusite1 and occasionally sillimanite and kyanite1 arise4 ,andalusite often forms grey prisms of irregular outline1 resembling slate-pencils1 and standing out above the mica on any weathered surface4 ,almandine garnet is almost always present4 ,quartz occurs in streaks and patches1 which resolve themselves into granular aggregates on microscopic examination4 ,the mica imparts a distinct foliation to the mass2 but the original stratification is very often preserved1 and the minerals have developed along its planes4 ,small differences in the constitution of the original strata give rise to different types of schist1 interbedded with one another4 ,andalusite1 for instance1 may occur only in certain argillaceous layers1 while other layers are quartzose1 through the presence of original sand4 ,mica-schist is the commonest type of metamorphic rock4 ,where mineralisation has taken place over a wide area1 it may be difficult to say if the foliation-planes in a schist are those of bedding1 or of superinduced cleavage1 or whether they indicate a sliding movement in the mass under pressure1 whereby all preceding structures have become obliterated4 ,amphibole-schist1 often styled epidiorite1 consists of foliated hornblende1 or its greener ally actinolite1 associated with granular felspar and sometimes with equally granular quartz4 ,the amphibole being usually prismatic1 the crystals are found with their longer axes arranged in parallel planes1 and often streaked out parallel to one another4 ,minute wrinklings1 due to subsequent yielding1 are not so frequent as in mica-schists4 ,amphibole-schists occur commonly as knots and somewhat irregular masses among mica-schists1 and represent basic igneous rocks that were interbedded or intrusive in the sedimentary series4 ,the pyroxene of the original rock has become recrystallised as hornblende1 and the felspathic constituent has rearranged itself in granular forms4 ,j4 ,j4 ,h4 ,teall#ie has described in interesting detail an example from the older rocks of ,sutherland1 and his paper contains a useful discussion of problems of pressure-metamorphism4 ,,amphibolites ,hornblende-schists are often seen to pass into true diorites2 but they also have relationships with the more puzzling rocks known as amphibolites4 ,these1 again1 graduate into pyroxenites1 or rocks rich in pyroxene1 with granular quartz and triclinic felspar1 and into eclogites1 which may be defined as pyroxenites with garnet4 ,pyroxene-eclogite1 in ,south ,africa1 is associated with diamond#if1 and fragments of exploded eclogite abound in the igneous vents from which the diamonds are extracted4 ,what has been called pyroxene-granulite is a dark granular eclogite1 including rhombic pyroxene side by side with garnet1 and associated1 in ,saxony and ,skye1 with igneous intrusions4 ,in both localities it has been shown to result from the inclusion of basic rocks1 such as dolerites and gabbros1 in a bath of some invading magma4 ,the lens-like form of the ,saxon masses1 and the occurrence also of sheets of pyroxene-granulite interlaminated with fine-grained granite1 were till lately attributed to the rolling-out action of pressure-metamorphism4 ,by what ,h4 ,credner calls a complete reversal of opinion1 due mainly to the opening of new railway-sections1 the granular eclogites of ,saxony are now regarded as products of extreme contact-alteration1 combined with igneous flow#ig4 ,a4 ,harker#ih similarly points out that examples in ,skye are derived from basaltic lavas1 into which gabbro has intruded1 producing a complete reconstruction of the rock4 ,where a series of igneous rocks and sediments1 in some cases already altered by pressure1 has been attacked and partly melted up by granite1 amphibolite-blocks are found as the common residue in the mingled mass4 ,the quartzites and mica-schists of the mantle that overlies the granite dome may have disappeared by stoping and absorption 7see p4 #abf74 ,rocks rich in amphibole remain1 and they commonly contain pyroxene as well as hornblende4 ,in some cases1 as in ,skye and ,saxony1 they may be traced to basic igneous rocks2 but in others they may be referred with equal certainty to limestone4 ,the interaction of the granite magma and the calcareous sediment has produced a silicate rock completely different from either4 ,lvy#ii and ,lacroix have shown how the amphibolites of ,france may sometimes represent dolerites1 sometimes limestones4 ,their work has recently received striking support from the observations of the ,geological ,survey of ,canada#ajj4 ,streaky hornblende-gneisses over wide areas of ,ontario are now attributed to the partial absorption of overlying limestone by what was once regarded as a fundamental granite4 ,the amphibolite blocks have become drawn out into bands that follow all the flow-structure of the invading igneous mass4 ,a small area of the same kind was studied in #aijj in north-west ,ireland#aja1 where a remarkably pure granitoid rock1 consisting of quartz and alkali felspar1 has become enriched with dark mica at the expense of blocks of amphibolite included in it4 ,,metamorphic ,,marbles ,,and ,,quartzites ,some of the changes that convert limestone into crystalline marble have already been referred to on pp4 #cf and #ed4 ,the presence of mica in limestones may allow of foliation when pressure comes to be applied to them1 and calc-schists result4 ,the mica may be detrital1 or may arise through the metamorphism of clayey bands2 but it forms weak layers1 along which the shearing movements take place which lead to a schistose structure in the mass4 ,pure granular marble may also occasionally become converted into a calc-schist1 by deformation of its crystalline grains along gliding planes within each crystal4 ,when we consider quartzites1 the same question rises as in the case of crystalline limestones1 and it is often difficult to state that a quartzite owes its characters to metamorphism4 ,microscopic examination sometimes reveals the effects of earth-pressures in the crushed and powdered condition of the larger grains2 and no rocks exhibit the power of such pressures in producing structural modifications more strikingly than the coarse quartz-grits that are sometimes involved in regions of dynamic metamorphism4 ,pebbles and grains are alike deformed1 pressed out along planes of fracture1 and finally reduced to bands of powdered quartz4 ,when felspathic pebbles occur in these grits1 the resulting schistose mass has almost the appearance of a banded igneous rock1 and streaky white mica may arise from the alteration of potassium felspar4 ,some sandstones contain sufficient felspar or calcium carbonate to form a flux when they are subjected to thermal metamorphism4 ,at times a glass thus arises between the grains1 and reacts upon the original quartz4 ,when the igneous magma has melted up a sandstone or a quartzite1 blocks of the sediment may remain surrounded by a mixed and recrystallised product from both rocks4 ,wright and ,bailey#ajb have studied an example in ,colonsay1 where a hornblende rock has partly dissolved a quartzite1 the residual blocks being surrounded by halos of interaction1 composed of quartz and alkali felspar4 ,,gneisses ,gneisses may be broadly defined as banded crystalline rocks in which felspar is visible to the unaided eye4 ,though this will include many igneous masses1 it is doubtful if a more rigid description can be given4 ,numerous gneisses1 in fact1 owe their parallel structures to flow while in a molten state4 ,others are rocks that have been deformed by pressure1 and their constituents have become drawn out along planes of solid flow4 ,where actual shearing has taken place1 the minerals in the close neighbourhood of the planes of movement may become especially modified1 ground down1 and deformed4 ,the foliated structure may then be marked by the appearance of differentiated bands4 ,such bands may also arise from the spreading out under pressure of certain large constituents1 such as porphyritic crystals of felspar1 which produce white bands1 or of pyroxene1 which will become modified into granular amphibole and will produce dark streaks through the rock4 ,illustration3 ,fig4 #ai4 ,composite ,gneiss4 ,gartan ,lough1 ,co4 ,donegal4 ,fragments of mica-schist project from a gneiss1 the banding of which follows the foliation planes of the schist4 ,on the right the mass retains less schist and is more granitic4 ,gneisses may also result from the intrusion of felspathic igneous rocks1 in sheets of varying thickness1 between the layers of a sediment or a schist 7,fig4 #ai72 or from the intrusion of one igneous rock into another1 with varying degrees of interaction and absorption4 ,it has often been presumed that the invaded igneous rock must have been in such cases in a plastic state4 ,the supply of heat within the earth during such processes1 and the action of the gases1 corroding1 as ,doelter says1 like a blowpipe-flame1 are1 however1 clearly sufficient to melt down large blocks1 the residue being then carried forward as wisps or bands in the invader4 ,many strikingly banded gneisses are thus of composite origin4 ,their felspathic granitoid bands can be traced in the field to an igneous source1 while their darker and usually micaceous layers can as surely be attributed to the invasion and incorporation of adjacent schists 7,fig4 #bj74 ,but it is quite possible that in other cases the banded gneiss is a sedimentary rock which has undergone what ,judd#ajc has styled statical metamorphism4 ,the differences in successive bands are then due to original differences in successive strata2 one has yielded a granitic layer1 one a layer of quartzite1 one1 which was more argillaceous1 a layer of mica-schist4 ,the bands in such a gneiss record the stratification4 ,illustration3 ,fig4 #bj4 ,composite ,gneiss formed by intrusion of granite into hornblende-schist4 ngn1 near ,saltsjbaden1 ,sweden4 ,gneisses are often described as if they consisted of layers of various minerals1 quartz1 felspar1 and mica1 alternating one with another4 ,as a matter of fact1 a gneiss may exist in which there is no differentiation into layers2 the whole of the constituents have been drawn out and elongated1 any mica present becoming naturally conspicuous by its flattened wisp-like forms4 ,the banded gneisses1 on the other hand1 where layer-structure is obvious1 consist in reality of bands of different rock-types4 ,sometimes all the layers are granitoid1 but one band will contain only quartz and felspar1 while another will contain the same minerals with an admixture1 and perhaps a great predominance1 of mica4 ,g4 ,p4 ,scrope#ajd made an immense step forward when he realised in #ahbe that such banded rocks1 the inferior crystalline zones1 might be pushed out of position and protruded among others in a solid or nearly solid state4 ,he goes on1 ,the protrusion of the foliated rocks1 gneiss1 mica-schist1 clay-slate1 etc4 was chiefly occasioned by their peculiar structure2 the parallel plane surfaces of their component crystals1 particularly the plates of mica1 sliding with facility over one another2 while the laminar structure of these rocks was in turn increased during this process1 the crystals being elongated in the direction of their motion1 as in the case of the clinkstones and pearl-stones of the trachytic formation4 ,after this1 there was little left for the later advocates of dynamo metamorphism to put forward4 ,while ,darwin#aje recognised how the granite at ,cape ,town had worked its way insidiously between the layers of a schist1 it was left for ,michel ,lvy to emphasise the part played by what is called lit-par-lit injection in the making of banded gneiss 7see p4 #abj74 ,k4 ,a4 ,lossen1 ,johann ,lehmann1 and other distinguished workers in ,germany made clear1 on the other hand1 the effects of pressure in moulding and reforming crystalline rocks1 and even in bringing about the crystallisation of certain minerals in a previously sedimentary mass4 ,the dynamo-metamorphic school assumed immense importance from #ahhd onwards1 the date of the publication of ,lehmann's work on ,die ,entstehung der altkrystallinischen ,schiefergesteine1 and for a time the intrusion of igneous masses was held1 both in ,germany and the ,british ,isles1 to have had a merely local significance as a metamorphic agent4 ,wherever regional metamorphism was spoken of1 pressure-effects were held to be predominant4 ,indeed1 the profound modifications that may occur in rocks when lowered into subterranean cauldrons is only now becoming generally realised4 ,the tendency to regard the structures of large masses of gneiss as of necessity due to deformation and shearing in a solid state has1 however1 passed away#ajf4 ,pressure-effects are of course clearly traceable in most gneisses1 and are of immense importance in many metamorphic areas2 but we find again and again that gneissic structure has been injured rather than developed by crushing subsequent to the consolidation of the rock4 ,in some cases1 where this structure is due to igneous flow1 which of course often took place under considerable pressure1 even the puckerings of the stratified or foliated rock which was invaded by the igneous magma have been followed by the invading sheets4 ,in other cases1 as in the composite amphibolite gneiss of ,canada1 or the similar rocks of the ,ox ,mountains in ,ireland1 the contortions in the mingled mass are clearly due to the viscid flow of the consolidating invader4 ,the growing appreciation of the views on recurrent thermal metamorphism that were originally propounded by ,james ,hutton in #aghe has led to the assignment of far younger ages to many masses previously regarded as fundamental and ,archan4 ,some of these rocks are undoubtedly of high antiquity1 but are found to be intrusive in strata of a late pre-,cambrian series4 ,others1 such as the material of the ,saxon laccolite1 and the gneisses on the north-east ,bohemian border1 are now known to be of ,upper ,palozoic age4 ,,the ,,question ,,of ,a ,,fundamental ,,gneiss ,ever since ,a4 ,c4 ,lawson#ajg showed in ,canada how the ,laurentian gneiss had invaded and swallowed up the overlying ,huronian rocks1 suspicion began to fall on the doctrine of a fundamental gneiss4 ,we may now well ask ourselves the following questions3-- 7i7 ,was there a time in the early history of our globe when schists and gneisses were deposited as a prevalent type of sediment1 under conditions which have not since recurred8 7ii7 ,if so1 which of the characters of these pre-,cambrian rocks are original1 and which have been acquired through subsequent metamorphism8 7iii7 ,on the other hand1 is the prevalence of gneiss and schist in early pre-,cambrian groups of rock due to the fact that1 the older the rock1 the more metamorphism1 by recurrent heat and pressure1 it is likely to have undergone8 7iv7 ,we may prefer the theory of ,laplace1 that the earth is cooling from a molten state2 or the planetesimal theory1 according to which heat has been developed during the consolidation and contraction of an agglomerate of solid particles2 yet in either case we must admit that the earth's outer layers were once nearer to the heated parts of the earth than they are now4 ,is it not likely1 then1 that early sediments became frequently immersed in baths of molten matter1 and that contact-metamorphism and admixture on a regional scale have produced in them the characters that have been attributed to a fundamental gneiss#ajh8 ,j4 ,j4 ,sederholm#aji has traced in ,finland four groups of ,archan sedimentary material1 which have been successively invaded by granite from the depths4 ,the bare wave-swept isles of ,spikarna1 east of ,hang1 serve as models of structures that are traceable throughout the ,baltic lands4 ,the more we regard the oldest gneisses of one region after another1 the more we see in them igneous matter that has attempted to assimilate sediments of still older date4 ,the banded structures that have been appealed to as indicating the power of earth-movements to deform the solid crystalline crust prove1 in very many cases1 to record the foliation of rocks that were already metamorphosed before the igneous matter spread among them4 ,in some of these cases1 this foliation followed planes of original stratification1 and we are forced to conclude that true sedimentary structure may after all control the features of a gnarled and contorted fundamental gneiss4 ,we are still far from discovering the primitive crust formed about a molten globe1 and the brilliant proofs of evolution in the organic world are unmatched by any evidence of the evolution of rock-types during geological time4 ,,metamorphic ,,rocks ,,and ,,scenery ,metamorphic rocks are usually associated with the scenery of mountain1 moor1 and forest4 ,the highly altered siliceous masses furnish but indifferent soils4 ,the connexion between metamorphic rocks and earth-crumpling1 and their frequent penetration by granite1 lead to the production of rugged ridges and high moorlands1 among which denudation has cut romantic glens4 ,the schists weather out on the valley-walls along their foliation-surfaces1 and scarps arise like those of stratified rocks4 ,the face of such a scarp is broken away in a zigzag and splintery fashion1 and the sharp edges of the foliated mass stand out like teeth upon the sky-line4 ,gneisses associated with the schists present a contrast of smoother surfaces1 wherever denudation has been long continued4 ,foliated diorites and amphibolites1 however1 may produce wild crags that even overhang2 while recently exposed gneiss1 at high altitudes1 may give rise to pinnacles and serrated forms4 ,where alternations of quartzite and mica-schist occur1 irregularities of the surface are readily maintained4 ,heather climbs upon the yellow soils furnished by the schist1 and trees may gather in its hollows2 but the quartzite stands out bare and dominant4 ,in some cases the upturned beds of the latter weather out like dykes across the country4 ,worn-down plateaus of ancient gneiss1 the mere residues of mountain-land1 may be seen in the storm-swept levels of the ,outer ,hebrides1 and in the hummocky country1 a swelling sea of bare grey rock and peat-filled hollows1 that borders all the west of ,sutherland4 ,the irregular weathering of mica-schist1 and the readiness with which it can be carved by streams1 control the bold landscapes of the highlands from the ,trossachs to ,lough ,ness1 and thence away again to the northern sea4 ,here and there1 great domes of intrusive granite rise amid the broken moorlands2 at times1 a white cone of quartzite catches the eye with a gleam like that of snow4 ,we may traverse this country as an introduction to the high glacial plateaus and deeply notched seaward slopes of the metamorphic lands of ,norway2 or to the contrasts of jagged schists and resisting gneisses that meets us as we near the ,alpine core4 ,,references 7,the numbers of volumes are given throughout in thick type2 the dates are between brackets1 and the page-references follow in ordinary figures47 ,footnote #a3 ,cordier1 ,mmoire sur les substances dites en masse1 qui entrent dans la composition des ,roches ,volcaniques1 ,journ4 de ,physique1 #hc 7#ahaf71 #ace1 #bhe1 and #ceb4 ,footnote #b3 ,on specific gravity of mineral grains see especially ,w4 ,j4 ,sollas1 ,nature1 #dc 7#ahia71 #djd4 ,footnote #c3 ,sorby1 ,q4 ,journ4 ,geol4 ,soc4 ,london1 #ad 7#aheh71 #dec4 ,footnote #d3 ,katzer1 ,geologischer ,fhrer durch ,bosnien1 ,,ix internat4 ,geologencongress 7#aijc71 #aij4 ,footnote #e3 ,a4 ,w4 ,rogers1 ,geology of ,cape ,colony1 ed4 #b 7#aiji71 #dja4 ,footnote #f3 ,linck1 ,die ,bildung der ,oolithe u4 ,rogensteine1 ,neues ,jahrb4 fr ,min41 #af 7#aijc71 #die4 ,footnote #g3 ,daly1 ,the ,limeless ,ocean1 ,amer4 ,journ4 ,sci41 ,ser4 #d1 #bc 7#aijg71 #ajd1 and ,evolution of the ,limestones1 ,bull4 ,geol4 ,soc4 ,amer4 #bj 7#aiji71 #aec4 ,footnote #h3 ,a4 ,r4 ,horwood1 ,geol4 ,mag4 7#aiaj71 #agc2 and ,cole and ,little1 ibid4 7#aiaa71 #di1 with references to literature4 ,footnote #i3 ,the ,atoll of ,funafuti1 ,roy4 ,soc4 ,london 7#aijd74 ,footnote #aj3 ,m4 ,ogilvie 7,gordon71 ,coral in the ,dolomites1 ,geol4 ,mag4 7#ahid71 #a and #di1 and later papers4 ,footnote #aa3 ,gardiner and ,reynolds1 ,the ,portraine ,inlier 7,co4 ,dublin71 ,q4 ,journ4 ,geol4 ,soc41 #ec 7#ahig71 #ecb4 ,footnote #iaa3 ,walther1 ,einleitung in die ,geologie als historische ,wissenschaft2 #cter4 ,theil1 ,lithogenesis der ,gegenwart 7#ahid71 #gjg4 ,footnote #ab3 ,see ,nichols1 ,field ,columbian ,museum1 ,geology1 #c 7#aijf74 ,footnote #ac3 ,skeats1 ,limestones from upraised coral islands1 ,bull4 ,mus4 ,comp4 ,zool4 ,harvard1 #db 7#aijc71 ,no4 #b4 ,footnote #ad3 ,see generally ,w4 ,meigen1 ,neuere ,arbeiten ber die ,entstehung des ,dolomits1 ,geol4 ,rundschau1 #a 7#aiaj71 #di4 ,footnote #ae3 ,skeats1 ,origin of the ,dolomites of southern ,tyrol1 ,q4 ,journ4 ,geol4 ,soc41 #fa 7#aije71 #ig4 ,footnote #af3 ,pfaff1 ,beitrge ber die ,entstehung des ,magnesits u4 ,dolomits1 ,neues ,jahrb4 fr ,min41 ,beilage ,bd4 #i 7#ahid71 #dhe4 ,footnote #ag3 ,garwood1 ,on the origin of the concretions in the ,magnesian ,limestone of ,durham1 ,geol4 ,mag4 7#ahia71 #dcc4 ,footnote #ah3 ,skeats1 op4 cit41 ref4 #ae1 p4 #ace4 ,footnote #ai3 ,j4 ,j4 ,h4 ,teall1 ,on dedolomitisation1 ,geol4 ,mag4 7#ahia74 #eac1 and ,rep4 ,brit4 ,assoc4 7#aijc74 ,footnote #bj3 ,j4 ,s4 ,howe1 ,geology of ,building ,stones 7#aiaj71 #cec4 ,footnote #ba3 ,hinde1 ,on ,beds of ,sponge remains in the south of ,england1 ,phil4 ,trans4 7#ahhe71 ,pt4 #b1 #dbg4 ,footnote #bb3 ,sollas1 ,on the structure of the genus ,catagma1 ,ann4 and ,mag4 ,nat4 ,hist41 ,ser4 #e1 #b 7#ahgh71 #cfa4 ,also ibid41 #f 7#ahhj71 #ddg4 ,footnote #bc3 ,cayeux1 tude micrographique des ,terrains sdimentaires1 ,mm4 ,soc4 ,gol4 du ,nord41 #d 7#ahig71 #ddc4 ,footnote #bd3 ,jukes-,browne1 ,the amount of disseminated silica in the ,chalk in relation to flints1 ,geol4 ,mag4 7#ahic71 #ede4 ,footnote #be3 ,guppy1 ,observations of a ,naturalist in the ,pacific3 ,vanua ,levu 7#aijc71 chap4 xxv4 ,footnote #bf3 ,rogers1 op4 cit41 ref4 #e1 p4 #djc4 ,footnote #bg3 ,judd1 ,on the unmaking of ,flints1 ,proc4 ,geol4 ,assoc41 #aj 7#ahhg71 #bag4 ,also ,hintze1 ,handbuch der ,mineralogie1 #a 7#aijf71 #adgc4 ,footnote #bh3 ,grund1 in ,stille's ,geologische ,charakterbilder1 ,heft #c 7#aiaj74 ,footnote #bi3 ,rullmann1 ,handbuch der technischen ,mykologie1 #c 7#aijd-f71 and refs4 in ,centralblatt fr ,bakteriologie 7#aijd and onwards74 ,footnote #cj3 ,hinde1 ,catalogue of ,fossil ,sponges1 ,brit4 ,mus4 7#ahhc71 #bh4 ,footnote #ca3 ,rogers1 ,geology of ,cape ,colony1 ed4 #a 7#aije71 #cgc4 ,footnote #cb3 ,ibid41 #ceg4 ,footnote #cc3 ,lyons1 ,libyan ,desert1 ,q4 ,journ4 ,geol4 ,soc41 #ej 7#ahid71 #ecd and #ede4 ,footnote #cd3 ,victorian ,naturalist1 #bg 7#aiaj71 #ij4 ,footnote #ce3 ,sorby1 ,structure and origin of non-calcareous stratified rocks1 ,q4 ,journ4 ,geol4 ,soc41 #cf 7#ahhj71 ,proc41 #fc4 ,footnote #cf3 ,phillips1 ,constitution and history of ,grits and ,sandstones1 ibid41 #cg 7#ahha71 #f4 ,footnote #cg3 ,a4 ,daubre1 ,geologie exprimentale 7#ahgi71 #bef4 ,footnote #ch3 ,phillips1 op4 cit41 ref4 #cf1 p4 #bf4 ,footnote #ich3 ,j4 ,barrell shows how wind-borne sand may form a covering to the dry and sun-cracked surface of a lake-deposit2 ,relation between climate and terrestrial deposits1 ,journ4 ,geol41 #af 7#aijh71 #bhj4 ,footnote #ci3 ,lake and ,rastall1 ,text-book of ,geology 7#aiaj71 #big4 ,compare ,c4 ,lapworth1 ,intermediate ,text-book of ,geology 7#ahii71 #agf1 and ,geological ,structure of ,n4 ,w4 ,highlands1 ,geol4 ,surv4 ,scotland 7#aijg74 ,footnote #ici3 ,see ,a4 ,b4 ,searle1 ,the ,natural ,history of ,clay 7#aiab74 ,footnote #dj3 ,hall1 ,the ,soil1 ed4 #b 7#aijh71 #cd1 and ,e4 ,j4 ,russell1 ,clay1 ,standard ,cyclopedia of ,modern ,agriculture 7#aijh74 ,footnote #da3 ,reade and ,holland1 ,sands and ,sediments1 ,proc4 ,liv4 ,geol4 ,soc4 7#aijc-f74 ,footnote #db3 ,andrussow1 ,la ,mer ,noire1 ,guide des ,excursions1 viime ,congrs gol4 internat4 7#ahig74 ,footnote #dc3 ,b4 ,smith1 ,upper ,keuper ,sandstone1 ,geol4 ,mag4 7#aiaj71 #cjb4 ,compare ,f4 ,cresswell1 ,trans4 ,leicester ,lit4 and ,phil4 ,soc4 7#aiaj74 ,footnote #dd3 ,j4 ,murray and ,a4 ,renard1 ,deep ,sea ,deposits1 ,challenger ,rep4 7#ahia71 #bca4 ,footnote #de3 ,ibid41 #bcd4 ,footnote #df3 ,ibid41 #bbi4 ,footnote #dg3 ,harker1 ,slaty ,cleavage and allied rock-structures1 ,rep4 ,brit4 ,assoc4 7#ahhe74 ,footnote #dh3 ,leith1 ,rock ,cleavage1 ,bull4 ,u4 ,s4 ,geol4 ,surv41 ,no4 #bci 7#aije74 ,footnote #di3 ,lamplugh1 ,geology of ,isle of ,man1 ,mem4 ,geol4 ,surv4 ,gt4 ,brit4 7#aijc71 #gb-hf4 ,footnote #ej3 ,darwin1 ,geological ,observations on ,s4 ,america 7#ahdf71 chap4 vi4 ,footnote #ea3 ,reade and ,holland1 ,green ,slates of the ,lake ,district1 with a ,theory of ,slaty ,cleavage1 ,proc4 ,liv4 ,geol4 ,soc4 7#aijj-a71 #abd4 ,footnote #eb3 ,a4 ,harker1 ,on 'eyes' of ,pyrites c41 ,geol4 ,mag4 7#ahhi71 #cif4 ,footnote #ec3 ,t4 ,n4 ,dale illustrates an extreme case1 ,slate ,deposits of ,u4,s41 ,bull4 ,u4,s4 ,geol4 ,surv41 ,no4 #bge 7#aijf71 #ca4 ,footnote #ed3 ,harker1 op4 cit41 ref4 #dg1 p4 #ai4 ,footnote #ee3 ,leith1 op4 cit41 ref4 #dh1 p4 #aeb4 ,footnote #ef3 ,i4 ,russell1 ,glaciers of ,n4 ,america 7#ahig71 #be4 ,footnote #eg3 ,see1 for instance1 ,t4 ,w4 ,edgeworth ,david1 ,evidences of glacial action in ,australia1 ,q4 ,journ4 ,geol4 ,soc41 #eb 7#ahif71 #bhi4 ,footnote #eh3 ,for general discussions of ,igneous ,rocks1 see ,j4 ,j4 ,h4 ,teall1 ,british ,petrography 7#ahhh72 ,h4 ,rosenbusch1 ,mikroskopische ,physiographie1 ed4 #d 7#aije-g72 ,f4 ,zirkel1 ,lehrbuch der ,petrographie1 ed4 #b 7#ahid72 ,a4 ,harker1 ,natural ,history of ,igneous ,rocks 7#aiji72 ,j4 ,p4 ,iddings1 ,igneous ,rocks1 #a 7#aiji74 ,footnote #ei3 ,cross1 ,iddings1 ,pirsson1 and ,washington1 ,quantitative ,classification of ,igneous ,rocks 7#aijc74 ,footnote #fj3 ,harker1 op4 cit41 ref4 #eh1 p4 #ahf4 ,footnote #fa3 ,iddings1 op4 cit41 ref4 #eh1 p4 #acj c4 ,footnote #fb3 ,ibid41 pp4 #bbh-bda4 ,footnote #fc3 ,scrope1 ,considerations on ,volcanos 7#ahbe71 #ada4 ,footnote #fd3 ,g4 ,a4 ,j4 ,cole and ,j4 ,w4 ,gregory1 ,variolitic ,rocks of ,mt ,genvre1 ,q4 ,journ4 ,geol4 ,soc41 #df 7#ahij71 #caa4 ,footnote #fe3 ,a4 ,geikie1 ,ancient ,volcanoes of ,gt ,britain1 #a 7#ahig71 #be4 ,also ,c4 ,reid and ,h4 ,dewey1 ,pillow lava of ,cornwall1 ,q4 ,journ4 ,geol4 ,soc41 #fd 7#aijh71 #bfd4 ,footnote #ff3 ,anderson1 ,volcano of ,matavanu1 ibid41 #ff 7#aiaj71 #fcb4 ,footnote #fg3 ,dewey and ,flett1 ,british ,pillow lavas1 ,geol4 ,mag4 7#aiaa71 #bjb and #bda4 ,footnote #fh3 ,steinmann1 ,die ,schardtsche ,ueberfaltungstheorie c41 ,ber4 nat4 ,gesell4 ,freiburg i4 ,b41 #af 7#aije71 #dd4 ,footnote #fi3 ,doelter1 ,petrogenesis 7#aijf71 #cc and #aji-abc4 ,footnote #gj3 ,harker1 op4 cit41 ref4 #eh1 p4 #hb4 ,footnote #ga3 ,iddings1 op4 cit41 ref4 #eh1 p4 #bhj4 ,footnote #gb3 ,brgger1 ,die ,eruptionsfolge bei ,predazzo1 ,vidensskab4 ,skrifter 7#ahie71 ,no4 #g1 p4 #aeb4 ,footnote #gc3 ,daly1 ,secondary origin of certain ,granites1 ,am4 ,journ4 ,sci41 ,ser4 #d1 #bj 7#aije71 #ahe1 with useful references to ,bayley and others4 ,footnote #gd3 ,hawes1 ,the ,albany granite and its contact phenomena1 ibid41 ,ser4 #c1 #ba 7#ahha71 #ca4 ,footnote #ge3 ,g4 ,a4 ,j4 ,cole1 ,geology of ,slieve ,gallion1 ,sci4 ,trans4 ,r4 ,dublin ,soc41 #f 7#ahig71 #bdb4 ,footnote #gf3 ,daly1 ,mechanism of igneous intrusion1 ,am4 ,journ4 ,sci41 ,ser4 #d1 #ae 7#aijc71 #bfi1 and later4 ,footnote #gg3 ,for a recent review in favour of this theory1 see ,loewinson ,lessing1 ,the fundamental problems of ,petrogenesis1 ,geol4 ,mag4 7#aiaa71 #bdh and #bhi4 ,footnote #gh3 ,darwin1 ,geological ,observations on volcanic islands 7#ahdd71 chap4 ,,vi4 ,footnote #gi3 ,brgger1 ,die ,eruptivgesteine des ,kristianiagebietes 7#ahid c474 ,footnote #hj3 ,harker1 op4 cit41 ref4 #eh1 chaps4 ,,xiii and ,,xiv4 ,footnote #ha3 ,daly1 ,origin of the alkaline rocks1 ,bull4 ,geol4 ,soc4 ,am41 #ba 7#aiaj71 #ajh1 and ,magmatic differentiation in ,hawaii1 ,journ4 ,geol41 #ai 7#aiaa71 #cji4 ,see1 however1 ,h4 ,i4 ,jensen1 as to primitive accumulation of alkalies in the upper layers2 ,the distribution of ,alkaline ,rocks1 ,proc4 ,linn4 ,soc4 ,n4 ,s4 ,w41 #cc 7#aijh71 #eba4 ,footnote #hb3 ,schwarz1 ,causal ,geology 7#aiaj74 ,footnote #hc3 ,doelter1 op4 cit41 ref4 #fi1 pp4 #ga-bac4 ,footnote #hd3 ,judd1 ,on ,tertiary gabbros c41 ,q4 ,journ4 ,geol4 ,soc41 #db 7#ahhf71 #ed4 ,footnote #he3 ,harker1 op4 cit41 ref4 #eh1 p4 #ij1 and ,nature 7,sept #aiaa71 #cai4 ,see also ,jensen1 ref4 #ha1 p4 #ebb4 ,footnote #hf3 ,dewey and ,flett1 op4 cit41 ref4 #fg1 p4 #bde4 ,footnote #hg3 ,steinmann1 op4 cit41 ref4 #fh1 p4 #fd4 ,footnote #hh3 ,see especially ,w4 ,j4 ,sollas1 ,the volcanic district of ,carlingford1 ,trans4 ,r4 ,i4 ,acad41 #cj 7#ahid71 #ejb4 ,footnote #hi3 ,a4 ,geikie1 op4 cit41 ref4 #fe1 #b1 #cdd and fig4 #cdh4 ,footnote #ij3 ,branner1 ,decomposition of rocks in ,brazil1 ,bull4 ,geol4 ,soc4 ,am41 #g 7#ahif71 #bee4 ,footnote #ij3 ,macculloch1 ,description of the ,western ,islands of ,scotland1 #a 7#ahai71 #bfg4 ,footnote #ib3 ,for general discussions of ,metamorphic ,rocks1 see ,a4 ,delesse1 tudes sur le ,mtamorphisme des ,roches 7#aheh72 ,lehmann1 ,untersuchungen ber die ,entstehung der altkrystallinischen ,schiefergesteine 7#ahhd72 ,a4 ,geikie1 ,text-book of ,geology 7#aijc71 #gfd-hjg and #gbh2 ,van ,hise1 ,a ,treatise on ,metamorphism1 ,u4 ,s4 ,geol4 ,survey1 ,mon4 #dg 7#aijd72 ,u4 ,grubenmann1 ,die krystallinen ,schiefer1 ed4 #b 7#aiji72 ,a4 ,geikie and others1 ,the ,geological ,structure of the ,n4 ,w4 ,highlands of ,scotland1 ,mem4 ,geol4 ,surv4 ,scotland 7#aijg74 ,footnote #ic3 ,d',aubuisson de ,voisins1 ,trait de ,geognosie 7#ahai71 #a1 #bih4 ,footnote #id3 ,darwin1 ref4 #ej4 ,footnote #ie3 ,teall1 ,metamorphosis of ,dolerite into ,hornblende-,schist1 ,q4 ,journ4 ,geol4 ,soc41 #da 7#ahhe71 #acc4 ,footnote #if3 ,t4 ,g4 ,bonney1 ,the parent rock of the diamond in ,s4 ,africa1 ,geol4 ,mag4 7#ahii71 #cji4 ,footnote #ig3 ,r4 ,lepsius1 ,geologie von ,deutschland1 #bter4 ,teil 7#aijc71 #adf and #afi2 ,h4 ,credner1 ,die ,genesis des schsischen ,granulitgebirges1 ,renuntiations-programm 7#aijf74 ,footnote #ih3 ,harker1 ,igneous ,rocks of ,skye1 ,mem4 ,geol4 ,surv4 ,scotland 7#aijd71 #aae4 ,footnote #ii3 ,lvy1 ,excursion ,aydat1 ,bull4 ,soc4 gol4 ,france 7#ahhc71 #iaf2 ,granite de ,flamanville1 ,bull4 ,carte gol4 ,france #e 7#ahic71 #ccg4 ,footnote #ajj3 ,f4 ,d4 ,adams1 ,haliburton and ,bancroft areas1 ,mem4 ,geol4 ,surv4 ,canada1 ,no4 #f 7#aiaj71 #abj4 ,footnote #aja3 ,g4 ,a4 ,j4 ,cole1 ,metamorphic rocks in ,e4 ,tyrone and ,s4 ,donegal1 ,trans4 ,r4 ,i4 ,acad41 #ca 7#aijj71 #dec4 ,footnote #ajb3 ,w4 ,b4 ,wright and ,e4 ,b4 ,bailey1 ,geology of ,colonsay1 ,mem4 ,geol4 ,surv4 ,scotland 7#aiaa71 #bh4 ,footnote #ajc3 ,judd1 ,statical and dynamical metamorphism1 ,geol4 ,mag4 7#ahhi71 #bdf4 ,footnote #ajd3 ,scrope1 op4 cit41 ref4 #fc1 p4 #bcd4 ,footnote #aje3 ,darwin1 op4 cit41 ref4 #gh1 chap4 ,,vii4 ,footnote #ajf3 ,see especially ,j4 ,horne and ,e4 ,greenly1 ,foliated ,granites c4 in ,e4 ,sutherland1 ,q4 ,journ4 ,geol4 ,soc41 #eb 7#ahif71 #fcc4 ,footnote #ajg3 ,lawson1 ,geology of ,rainy ,lake ,region1 ,ann4 ,rep4 ,geol4 ,surv4 ,canada for #ahhg 7#ahhh74 ,footnote #ajh3 ,compare ,chamberlin and ,salisbury1 ,college ,text-book of ,geology 7#aiji71 #dbh1 and other works by these authors4 ,footnote #aji3 ,sederholm1 ,om granit och gneis i ,fennoskandia 7with ,english summary71 ,bull4 ,comm4 gol4 ,finlande1 ,no4 #bc 7#aijg71 and elsewhere4 ,,table ,,of ,,stratigraphical ,,systems ,quaternary ,group ,post-,pliocene and ,recent ,cainozoic ,group ,pliocene ,miocene ,oligocene ,eocene ,mesozoic ,group ,cretaceous ,jurassic ,triassic ,palozoic ,group ,permian ,carboniferous ,devonian ,gotlandian 7 ,silurian or ,upper ,silurian7 ,ordovician 7or ,lower ,silurian7 ,cambrian ,pre-,cambrian ,group ,,index 7,ref indicates that the name is quoted in the list of references1 pp4 #afb-afi47 ,acid igneous rocks1 #abg1 #acb ,adams1 ,f4 ,d41 #abe1 ref4 #ajj ,africa1 ,s41 #adh4 ,see ,cape of ,good ,hope and ,rhodesia4 ,agassiz1 ,a41 #be2 ,l41 #ih ,agents minralisateurs1 #ajg ,alg1 calcareous1 #be ,alkaline igneous rocks1 #abi ,alps1 #ad1 #af1 #bc1 #ach1 #adc1 #afb ,ammonites1 #bc ,amphibole-,schist1 #adg ,amphibolite1 #adh ,anderson1 ,t41 #aag ,andesite1 #acc ,andrussow1 ,n41 #hd ,antrim1 ,co41 #df1 #ace ,aragonite1 deposition of1 #ag2 in shells1 #bb1 #hf ,armitage1 #fd ,ash1 #hh1 #aaa ,assimilation in igneous rocks1 #abh ,atlantic and ,pacific types of igneous rocks1 #acj ,auvergne1 #aab ,axmouth1 #df ,bacteria1 extraction of iron by1 #fa ,bagshot ,heath1 #gc ,bailey1 ,e4 ,b41 ref4 #ajb ,banded structure1 #abj ,barrell1 ,j41 ref4 #ich ,barrois1 ,c41 #abe ,barytes in sandstone1 #fb ,basalt1 #acb1 #ace ,basic igneous rocks1 #abg1 #acb ,batholites1 #abc ,bavaria1 dolomites of1 #cb ,belemnites1 #bc ,black ,sea1 #ag1 #hd ,bohemia1 #acd1 #aeh ,bonney1 ,t4 ,g41 ref4 #if ,boulder-clay1 #if ,bournes1 #dc ,brachiopods1 #bd ,branner1 ,j4 ,c41 #adj ,brazil1 #hh1 #adj ,breccia1 #ee ,brgger1 ,w4 ,c41 #abe1 #abh ,brongniart1 ,a41 #b ,bunsen1 ,r4 ,w41 #abg ,cader ,idris1 #adc ,calcareous ,tufa1 #ad1 #af ,canada1 #ajc1 #aej1 #aeh ,caons of ,arizona1 #dg ,cape of ,good ,hope1 #af1 #da1 #ei1 #fc1 #ajc1 #aba1 #acf1 #aef ,causses1 #de1 #dh1 #ej ,cayeux1 ,l41 #ci ,cephalopods1 #bc ,chalk1 #bj1 #db ,chamberlin1 ,t4 ,c41 #abi ,chara-limestone1 #ai ,cheddar1 #dh ,chert1 #dj1 #fb ,china-clay1 #hf ,christiania district1 #abe1 #abh ,christmas ,island1 #cg ,clare1 ,co41 #df ,clay1 #gh ,cleavage1 #hi ,close1 ,maxwell ,h41 #ih ,cole1 ,g4 ,a4 ,j41 #aag1 refs4 #h1 #ge and #aja ,coleman1 ,a4 ,c41 #ajc ,colonsay1 #aeb ,columnar structure1 #aae ,composite gneiss1 #abb1 #aec ,cones1 volcanic1 #aab1 #acc ,conglomerates1 #gj ,connemara marble1 #cf ,contact metamorphism1 #add ,conybeare1 ,w4 ,d41 #ce ,coral-reefs1 #be2 silicification in1 #dj ,cordier1 ,p4 ,l4 ,a41 #c ,cork marble1 #ed ,credner1 ,h41 #abe1 #adi ,crinoidal limestone1 #bd ,cross1 ,w41 ref4 #ei ,crush-conglomerates1 #bh ,crystallisation in igneous rocks1 #ajg ,dale1 ,t4 ,n41 ref4 #ec ,daly1 ,r4 ,a41 #ah1 #cc1 #abe1 #abg1 #abh ,dana1 ,j4 ,d41 #cj ,darwin1 ,c41 #be1 #ij1 #abh1 #ade1 #aef ,daubre1 ,a41 #ff ,d',aubuisson de ,voisins1 #ade ,david1 ,t4 ,w4 ,e41 ref4 #eg ,dedolomitisation1 #ce ,de la ,beche1 ,h41 #ah ,delesse1 ,a41 ref4 #ib ,derbyshire1 #dh1 #gc1 #ig ,desert sands1 #fh1 #ga ,dewey1 ,h41 #aag1 #acj ,diatoms1 #dj ,differentiation in igneous rocks1 #abh ,dinaric ,alps1 #af1 #bc1 #eb ,diorite1 #acb ,doelter1 ,c41 #ah1 #ca1 #abe1 #acj1 #aed ,dolerite1 #acb ,dolinas1 #ej ,dolomite1 #ab1 #bf1 #bi1 #cj ,donegal1 ,co41 #acg1 #aej1 #aec ,down1 ,co41 #gd1 #acg ,dreikanter1 #ga ,drumlins1 #ih1 #ajb ,durham1 dolomite of1 #ce ,durocher1 ,j41 #abg ,dwyka ,conglomerate1 #ajc ,dykes1 #aaj1 #aah1 #acg ,dynamo-metamorphism1 #add ,eclogite1 #adh ,edinburgh1 #adc ,egypt1 #bb1 #fd1 #fh ,ehrenberg1 ,c4 ,g41 #e1 #bj ,epidiorite1 #adg ,eurite1 #acb ,eutectic proportion1 #aji ,exfoliation of granite1 #adj ,felsitic structure1 #ajh ,ferromagnesian minerals1 #aji ,fiji ,is41 #dj ,fingal's ,cave1 #aaf ,finland1 #aei ,flagstones1 #fi ,flett1 ,j4 ,s41 #aag1 #acj ,flint1 #ch1 #fb2 gravels1 #gd ,flocculation of clay1 #hj ,flow-cleavage1 #ib ,fluidal structure1 #abj ,foliation1 #ij1 #ade ,foraminifera1 #bj ,forehammer1 ,g41 #bi ,fracture-cleavage1 #ib ,freshwater molluscs1 #bc ,fuji-yama1 #acd ,funafuti atoll1 #ai1 #bf ,fundamental gneiss1 #aeh ,fusulina limestone1 #ba ,gabbro1 #acb1 #adb ,gardiner1 ,c41 #bi ,garwood1 ,e4 ,j41 #ce ,geikie1 ,a41 #aag1 #ach1 #adb ,giant's ,causeway1 #aaf ,gilbert1 ,g4 ,k41 #abc ,glacial gravels1 #ih ,glaciers1 arctic1 #ih ,glassy igneous rocks1 #aaj ,glauconite in chalk1 #bj ,globigerina-ooze1 #bj ,gneiss1 #abb1 #aeb1 #aeh1 #afa ,gordon1 ,m4 ,ogilvie1 #bg ,granite1 #acb1 #ach ,granodiorite1 #acb ,great ,salt ,lake1 ,utah1 #ae ,great ,whin ,sill1 #acf ,greenly1 ,e41 ref4 #ajf ,gregory1 ,j4 ,w41 #aag ,greywacke1 #eh ,grund1 ,a41 #ej ,guppy1 ,h4 ,b41 #dj ,halimeda1 #ai1 #bi ,hall1 ,a4 ,d41 #ha ,harker1 ,a41 #hi1 #ajg1 #abe1 #abh1 #acj1 #adi ,harlech ,beds1 #gd ,hawaii1 #ajf ,hawes1 ,g4 ,v41 #abf ,hebrides1 #aaf1 #ace1 #aeb1 #afa ,hegau1 the1 #ace ,henry ,mountains1 ,utah1 #abc ,hercegovina1 karstland1 #ad1 #eb ,highlands of ,scotland1 #gf1 #adc1 #afa ,hinde1 ,g4 ,j41 #ch1 #fb ,holland1 ,p41 #hc1 #ij ,hornblende-,schist1 #adg ,horne1 ,j41 ref4 #ajf ,horwood1 ,a4 ,b41 ref4 #h ,howe1 ,j4 ,a41 #ac ,hutton1 ,j41 #da1 #ajd1 #abb1 #aeh ,hydrozoa1 #be ,iddings1 ,j4 ,p41 #ajh1 #aae1 #abe1 ref4 #ei ,igneous ,rocks1 #ajc ,india1 #adj ,intermediate igneous rocks1 #abg1 #acb ,intrusion of igneous rocks1 #abd ,intrusive sheets1 #abb1 #acf ,irish ,channel1 limestone in1 #ag ,iron-bacteria1 #fa ,iron ,pyrites in muds1 #he ,jajce1 #af ,jensen1 ,h4 ,t41 ref4 #ha ,judd1 ,j4 ,w41 #f1 #db1 #fh1 #ajd1 #acj1 #aed ,jukes-,browne1 ,a41 #dj ,jura ,mts41 #df ,kalahari desert1 #da1 #fc ,kaolin1 #hg ,karlsbad1 #ad ,karst1 #di ,katzer1 ,f41 #af ,kerry1 #gf ,klement1 ,c41 #ca ,knoll structure1 #bh ,laccolites1 #abc ,lacroix1 ,a41 #ae1 #abe1 #aej ,lake1 ,p41 #gf ,lamellibranchs1 #bb ,lamplugh1 ,g4 ,w41 #hi ,landslips1 #df1 #id ,lapworth1 ,c41 ref4 #ci ,laterisation1 #fd ,laurentian gneiss1 #aeh ,lautaret ,pass1 #ie ,lava-flows1 #aac ,lava-plains1 #aad ,lawson1 ,a4 ,d41 #abe1 #aeh ,lehmann1 ,j41 #aeg ,leinster granite1 #adc ,leith1 ,c4 ,k41 #hi ,leith ,hill1 #gc ,leonhard1 ,k4 von1 #c ,lepsius1 ,r41 #abe1 ref4 #ig ,lessing1 ,l41 ref4 #gg ,lvy1 ,m41 #f1 #abe1 #aej1 #aef ,limestones1 #ab1 #aej2 deposited from solution1 #ad2 organic1 #ai ,linck1 ,g41 #af1 #ah1 #fa ,lit-par-lit injection1 #aeg ,lithoidal structure1 #ajh ,lithothamnium1 #bj1 #bi ,little1 ,o4 ,h41 ref4 #h ,llanberis1 #if ,loam1 #hb ,londonderry1 ,co41 #ace ,lossen1 ,k4 ,a41 #aeg ,lower ,greensand1 #fb1 #gc ,lundy ,id41 #aci ,lyons1 ,h4 ,g41 #fc ,macculloch1 ,j41 #adb ,magmas1 igneous1 #abg ,magmatic differentiation1 #abh ,magnesian limestone1 #ce ,magnesium in organic skeletons1 #bi ,marble1 #cf1 #ed1 #aej ,marl1 #hc ,martel1 ,e4 ,a41 #eb ,matopo ,hills1 #adj ,matterhorn1 #adc ,metamorphic ,rocks1 #adc ,mica-,schist1 #adg1 #afa ,millepora1 #be ,millersdale1 #dh ,minerals1 #f1 #h ,mojsisovics1 ,e41 #bg ,monaghan1 ,co41 #gd ,mont ,blanc1 #ach1 #adc ,mont ,genvre1 #aag ,mull1 #ace ,murray1 ,j41 #be ,nagelfluh1 #ad ,new ,forest1 #gd ,northumberland1 #acf ,norway1 #afb ,nubian ,sandstone1 #fc ,nummulitic limestone1 #ba ,obsidian1 #acb ,old ,red ,sandstone1 #ge ,oolitic grains1 #ae1 #ag ,oolitic ,limestone1 #ah1 #dj ,ophicalcite1 #cf ,order of crystallisation of minerals1 #ajh ,ox ,mountains1 #aeh ,paris basin1 #dj1 #gd ,petrographical provinces1 #acj ,pfaff1 #cj1 #cd ,phillips1 ,j4 ,a41 #fd1 #fg ,phillips1 ,w41 #ce ,phosphatic limestone1 #cf ,phosphorites du ,quercy1 #cg ,pillow-structure1 #aag ,pipe-clay1 #gh ,pisolite1 #ae1 #ah ,planetesimal theory1 #abi1 #acj1 #aei ,plutonic conditions1 #aai ,porosity of sandstone1 #ff2 of clay1 #gi ,porphyritic structure1 #aai ,portland stone1 #ah ,portrane1 ref4 #aa ,purbeck ,marble1 #ed ,pyroxenite1 #adh ,quartz veins1 #ef1 #fe ,quartz-felsite1 #acb ,quartzite1 #fc1 #gf1 #aea1 #afa ,quartz-porphyry1 #acb ,radiolaria1 #dj1 #aah ,ravines in limestone1 #dh ,reade1 ,t4 ,m41 #hc1 #ij ,red ,clay of deep seas1 #hh ,regional metamorphism1 #aeg ,reynolds1 ,s4 ,h41 #bi ,rhodesia1 #adj ,rhyolite1 #acb ,richthofen1 ,f4 von1 #be1 #bg ,ripple-marks1 #fi ,rock1 definition of1 #g ,roestone1 #ae ,rogers1 ,a4 ,w41 #da1 #fb1 #fc ,rosenbusch1 ,h41 #f1 ref4 #eh ,rothpletz1 ,a41 #bg ,russell1 ,e41 #hb ,russell1 ,i41 ref4 #ef ,samoa1 #aag ,sand-dunes1 #fb1 #fi ,sand-rock1 #fe ,sands1 origin1 #ef2 cementing of1 #fj2 grains1 #ff ,sandstones1 #ef2 crystalline1 #fd ,saxony1 #adh1 #adi1 #aeh ,sea1 action of on shore1 #eh1 #hg2 calcium carbonate in1 #af ,searle1 ,a4 ,b41 ref4 #ici ,sederholm1 ,j4 ,j41 #abe1 #aei ,semper1 ,k41 #be ,serpentine1 #acc ,schists1 #ade1 #afa ,schwarz1 ,e4 ,h4 ,l41 #abi ,scori1 #aab ,scoriaceous structure1 #ajf ,scrope1 ,g4 ,p41 #ajd1 #aaf1 #ade1 #aef ,shale1 #hc1 #if2 colours of1 #he ,sharpe1 ,d41 #hi ,shell-marl1 #bc ,silicates in igneous rocks1 #aji ,silicified wood1 #fd ,sills1 igneous1 #acf ,skeats1 ,e4 ,w41 #cj1 #ca1 #ce ,skye1 #ace1 #ach1 #adb1 #adi ,slate1 #hh1 #if ,smith1 ,b41 #hf ,snowdon1 #adc ,sollas1 ,w4 ,j41 #ch1 refs4 #b and #hh ,sorby1 ,h4 ,c41 #e1 #fd1 #ff1 #hi1 #ij ,southern ,uplands1 #gd ,spherulites1 #ajh ,spilitic lavas1 #aag1 #aca ,spitsbergen1 #bj1 #ha1 #ii1 #aja ,sponges1 siliceous1 #ch1 #fb ,steinmann1 ,g41 #aah1 #aca ,stoping process1 #abf ,strain-slip cleavage1 #ib ,sun-cracks1 #fi ,surrey ,hills1 #dc1 #gc ,swallow-holes1 #dd ,sweden1 gneiss of1 #aee ,syenite1 #acb ,teall1 ,j4 ,j4 ,h41 #aag1 #adh ,terra rossa1 #ej ,terrace-structure in limestone1 #df2 in basalt1 #ace ,thames1 material in solution1 #ag ,torridon ,sandstone1 #gf ,tors1 #ach ,trachyte1 #acc ,travertine1 #ae ,tridacna1 #bc ,trieste1 #ej ,tuff1 #aaa ,tyrol1 dolomites1 #bf1 #ca1 #ec ,ultrabasic igneous rocks1 #acb ,van ,hise1 ,c4 ,r41 #adc ,vesuvius1 #aaa ,victoria1 ,australia1 #fd ,volcanic ash1 #hh1 #aaa2 cones1 #aab1 #acc2 dust1 #aaa2 necks1 #abb1 #acd2 tuff1 #aaa ,walther1 ,j41 #bi ,weald1 #gc ,weathering in tropics1 #fd1 #adj ,west ,indies1 #ah1 #cg ,whinstone1 #acg ,wright1 ,w4 ,b41 #aeb ,yellowstone ,park1 #ae ,yoredale1 #gc ,zirkel1 ,f4 von1 #f1 ref4 #eh ,cambridge3 ,,printed ,,by ,,john ,,clay1 ,m4,a4 ,,at ,,the ,,university ,,press ,,the ,,cambridge ,,manuals ,,of ,,science ,,and ,,literature ,published by the ,cambridge ,university ,press under the general editorship of ,p4 ,giles1 ,litt4,d41 ,master of ,emmanuel ,college1 and ,a4 ,c4 ,seward1 ,f4,r4,s41 ,professor of ,botany in the ,university of ,cambridge4 ---------------------------------------- -------------- ,a series of handy volumes dealing with a wide range of subjects and bringing the results of modern research and intellectual activity within the reach both of the student and of the ordinary reader4 ---------------------------------------- -------------- ,,history ,,and ,,archaeology #db ,ancient ,assyria4 ,by ,rev4 ,c4 ,h4 ,w4 ,johns1 ,litt4,d4 #ea ,ancient ,babylonia4 ,by ,rev4 ,c4 ,h4 ,w4 ,johns1 ,litt4,d4 #dj ,a ,history of ,civilization in ,palestine4 ,by ,prof4 ,r4 ,a4 ,s4 ,macalister1 ,m4,a41 ,f4,s4,a4 #gh ,the ,peoples of ,india4 ,by ,j4 ,d4 ,anderson1 ,m4,a4 #di ,china and the ,manchus4 ,by ,prof4 ,h4 ,a4 ,giles1 ,,ll4,d4 #gi ,the ,evolution of ,new ,japan4 ,by ,prof4 ,j4 ,h4 ,longford4 #dc ,the ,civilization of ,ancient ,mexico4 ,by ,lewis ,spence4 #fj ,the ,vikings4 ,by ,prof4 ,allen ,mawer1 ,m4,a4 #bd ,new ,zealand4 ,by the ,hon4 ,sir ,robert ,stout1 ,k4,c4,m4,g41 ,,ll4,d41 and ,j4 ,logan ,stout1 ,,ll4,b4 7,n4,z474 #he ,military ,history4 ,by the ,hon4 ,j4 ,w4 ,fortescue4 #hd ,the ,royal ,navy4 ,by ,john ,leyland4 #gf ,naval ,warfare4 ,by ,j4 ,r4 ,thursfield1 ,m4,a4 #ae ,the ,ground ,plan of the ,english ,parish ,church4 ,by ,a4 ,hamilton ,thompson1 ,m4,a41 ,f4,s4,a4 #af ,the ,historical ,growth of the ,english ,parish ,church4 ,by ,a4 ,hamilton ,thompson1 ,m4,a41 ,f4,s4,a4 #fh ,english ,monasteries4 ,by ,a4 ,h4 ,thompson1 ,m4,a41 ,f4,s4,a4 #ej ,brasses4 ,by ,j4 ,s4 ,m4 ,ward1 ,b4,a41 ,f4,r4,hist4,s4 #ei ,ancient ,stained and ,painted ,glass4 ,by ,f4 ,s4 ,eden4 #hj ,a ,grammar of ,english ,heraldry4 ,by ,w4 ,h4 ,st ,j4 ,hope1 ,litt4,d4 ,,economics #gj ,copartnership in ,industry4 ,by ,c4 ,r4 ,fay1 ,m4,a4 #f ,cash and ,credit4 ,by ,d4 ,a4 ,barker4 #fg ,the ,theory of ,money4 ,by ,d4 ,a4 ,barker4 #hf ,economics and ,syndicalism4 ,by ,prof4 ,a4 ,w4 ,kirkaldy4 ,,literary ,,history #h ,the ,early ,religious ,poetry of the ,hebrews4 ,by the ,rev4 ,e4 ,g4 ,king1 ,d4,d4 #ba ,the ,early ,religious ,poetry of ,persia4 ,by the ,rev4 ,prof4 ,j4 ,hope ,moulton1 ,d4,d41 ,d4,theol4 7,berlin74 #i ,the ,history of the ,english ,bible4 ,by ,john ,brown1 ,d4,d4 #ab ,english ,dialects from the ,eighth ,century to the ,present ,day4 ,by ,w4 ,w4 ,skeat1 ,litt4,d41 ,d4,c4,l41 ,f4,b4,a4 #bb ,king ,arthur in ,history and ,legend4 ,by ,prof4 ,w4 ,lewis ,jones1 ,m4,a4 #ed ,the ,icelandic ,sagas4 ,by ,w4 ,a4 ,craigie1 ,,ll4,d4 #bc ,greek ,tragedy4 ,by ,j4 ,t4 ,sheppard1 ,m4,a4 #cc ,the ,ballad in ,literature4 ,by ,t4 ,f4 ,henderson4 #cg ,goethe and the ,twentieth ,century4 ,by ,prof4 ,j4 ,g4 ,robertson1 ,m4,a41 ,ph4,d4 #ci ,the ,troubadours4 ,by the ,rev4 ,h4 ,j4 ,chaytor1 ,m4,a4 #ff ,mysticism in ,english ,literature4 ,by ,miss ,c4 ,f4 ,e4 ,spurgeon4 ,,philosophy ,,and ,,religion #d ,the ,idea of ,god in ,early ,religions4 ,by ,dr ,f4 ,b4 ,jevons4 #eg ,comparative ,religion4 ,by ,dr ,f4 ,b4 ,jevons4 #fi ,plato3 ,moral and ,political ,ideals4 ,by ,mrs ,j4 ,adam4 #bf ,the ,moral ,life and ,moral ,worth4 ,by ,prof4 ,sorley1 ,litt4,d4 #c ,the ,english ,puritans4 ,by ,john ,brown1 ,d4,d4 #aa ,an ,historical ,account of the ,rise and ,development of ,presbyterianism in ,scotland4 ,by the ,rt ,hon4 the ,lord ,balfour of ,burleigh1 ,k4,t41 ,g4,c4,m4,g4 #da ,methodism4 ,by ,rev4 ,h4 ,b4 ,workman1 ,d4,lit4 ,,education #ch ,life in the ,medieval ,university4 ,by ,r4 ,s4 ,rait1 ,m4,a4 ,,law #ac ,the ,administration of ,justice in ,criminal ,matters 7in ,england and ,wales74 ,by ,g4 ,glover ,alexander1 ,m4,a41 ,,ll4,m4 ,,biology #a ,the ,coming of ,evolution4 ,by ,prof4 ,j4 ,w4 ,judd1 ,c4,b41 ,f4,r4,s4 #b ,heredity in the ,light of ,recent ,research4 ,by ,l4 ,doncaster1 ,sc4,d4 #be ,primitive ,animals4 ,by ,geoffrey ,smith1 ,m4,a4 #gc ,the ,life-story of ,insects4 ,by ,prof4 ,g4 ,h4 ,carpenter4 #dh ,the ,individual in the ,animal ,kingdom4 ,by ,j4 ,s4 ,huxley1 ,b4,a4 #bg ,life in the ,sea4 ,by ,james ,johnstone1 ,b4,sc4 #ge ,pearls4 ,by ,prof4 ,w4 ,j4 ,dakin4 #bh ,the ,migration of ,birds4 ,by ,t4 ,a4 ,coward4 #cf ,spiders4 ,by ,c4 ,warburton1 ,m4,a4 #fa ,bees and ,wasps4 ,by ,o4 ,h4 ,latter1 ,m4,a4 #df ,house ,flies4 ,by ,c4 ,g4 ,hewitt1 ,d4,sc4 #cb ,earthworms and their ,allies4 ,by ,f4 ,e4 ,beddard1 ,f4,r4,s4 #gd ,the ,flea4 ,by ,h4 ,russell4 #fd ,the ,wanderings of ,animals4 ,by ,h4 ,f4 ,gadow1 ,f4,r4,s4 ,,anthropology #bj ,the ,wanderings of ,peoples4 ,by ,dr ,a4 ,c4 ,haddon1 ,f4,r4,s4 #bi ,prehistoric ,man4 ,by ,dr ,w4 ,l4 ,h4 ,duckworth4 ,,geology #ce ,rocks and their ,origins4 ,by ,prof4 ,grenville ,a4 ,j4 ,cole4 #dd ,the ,work of ,rain and ,rivers4 ,by ,t4 ,g4 ,bonney1 ,sc4,d4 #g ,the ,natural ,history of ,coal4 ,by ,dr ,e4 ,a4 ,newell ,arber4 #cj ,the ,natural ,history of ,clay4 ,by ,alfred ,b4 ,searle4 #cd ,the ,origin of ,earthquakes4 ,by ,c4 ,davison1 ,sc4,d41 ,f4,g4,s4 #fb ,submerged ,forests4 ,by ,clement ,reid1 ,f4,r4,s4 #gb ,the ,fertility of the ,soil4 ,by ,e4 ,j4 ,russell1 ,d4,sc4 ,,botany #e ,plant-,animals3 a ,study in ,symbiosis4 ,by ,prof4 ,f4 ,w4 ,keeble4 #aj ,plant-,life on ,land4 ,by ,prof4 ,f4 ,o4 ,bower1 ,sc4,d41 ,f4,r4,s4 #ai ,links with the ,past in the ,plant-,world4 ,by ,prof4 ,a4 ,c4 ,seward1 ,f4,r4,s4 ,,physics #eb ,the ,earth4 ,by ,prof4 ,j4 ,h4 ,poynting1 ,f4,r4,s4 #ec ,the ,atmosphere4 ,by ,a4 ,j4 ,berry1 ,m4,a4 #ha ,the ,sun4 ,by ,prof4 ,r4 ,a4 ,sampson1 ,d4,sc41 ,f4,r4,s4 #fe ,beyond the ,atom4 ,by ,john ,cox1 ,m4,a4 #ee ,the ,physical ,basis of ,music4 ,by ,a4 ,wood1 ,m4,a4 #ga ,natural ,sources of ,energy4 ,by ,prof4 ,a4 ,h4 ,gibson1 ,d4,sc4 ,,psychology #ad ,an ,introduction to ,experimental ,psychology4 ,by ,dr ,c4 ,s4 ,myers4 #de ,the ,psychology of ,insanity4 ,by ,bernard ,hart1 ,m4,d4 #gg ,the ,beautiful4 ,by ,vernon ,lee4 ,,industrial ,,and ,,mechanical ,,science #ca ,the ,modern ,locomotive4 ,by ,c4 ,edgar ,allen1 ,a4,m4,i4,mech4,e4 #ef ,the ,modern ,warship4 ,by ,e4 ,l4 ,attwood4 #ag ,aerial ,locomotion4 ,by ,e4 ,h4 ,harper1 ,m4,a41 and ,allan ,e4 ,ferguson1 ,b4,sc4 #ah ,electricity in ,locomotion4 ,by ,a4 ,g4 ,whyte1 ,b4,sc4 #fc ,wireless ,telegraphy4 ,by ,prof4 ,c4 ,l4 ,fortescue1 ,m4,a4 #eh ,the ,story of a ,loaf of ,bread4 ,by ,prof4 ,t4 ,b4 ,wood1 ,m4,a4 #dg ,brewing4 ,by ,a4 ,chaston ,chapman1 ,f4,i4,c4 #hb ,coal-,mining4 ,by ,t4 ,c4 ,cantrill4 #hc ,leather4 ,by ,prof4 ,h4 ,r4 ,procter4 ,a very valuable series of books which combine in a very happy way a popular presentation of scientific truth along with the accuracy of treatment which in such subjects is essential4444 ,in their general appearance1 and in the quality of their binding1 print1 and paper1 these volumes are perhaps the most satisfactory of all those which offer to the inquiring layman the hardly earned products of technical and specialist research4--,spectator ,a complete set of these manuals is as essential to the equipment of a good school as is an encyclopaedia4444 ,we can conceive no better series of handy books for ready reference than those represented by the ,cambridge ,manuals4--,school ,world ,cambridge ,university ,press ,c4 ,f4 ,clay1 ,manager ,,london3 ,fetter ,lane1 ,e4,c4 ,,edinburgh3 #ajj ,princes ,street 99 99 99 99 99 ,transcriber ,note ,minor typos corrected4 ,the volume used endnotes which had several duplicated numbers with a bis extension4 ,those numbers were changed to #ijj the original number4 ,there is no anchor for ,footnote #cg and #f and #g have more than one anchor in the text4