,,the ,,elements ,,of ,,geology2 ,,adapted ,,to ,,the ,,use ,,of ,,schools ,,and ,,colleges4 ,,by ,,justin ,r4 ,,loomis1 ,,professor ,,of ,,chemistry ,,and ,,geology ,,in ,,waterville ,,college4 ,,with ,,numerous ,,illustrations4 ,,boston3 ,,gould ,,and ,,lincoln1 #ei ,,washington ,,street4 #aheb ,entered according to ,act of ,congress1 in the year #aheb1 ,by ,,gould ,,lincoln1 ,in the ,clerk's ,office of the ,district ,court of the ,district of ,massachusetts4 ,stereotyped by ,,hobart ,,robbins1 ,,boston4 ,,press ,,of ,g4 ,c4 ,,rand1 ,,cornhill1 ,,boston4 ,,preface ,in preparing the following work1 it was intended to present a systematic and somewhat complete statement of the principles of ,geology1 within such limits that they may be thoroughly studied in the time usually allotted to this science4 ,a sufficient number of leading facts has been introduced to enable the learner to feel that every important principle is a conclusion to which he has himself arrived2 and yet1 for the purpose of compression1 that fullness of detail has been avoided with which more extended works abound4 ,in furtherance of the same object1 authorities are seldom cited4 ,the consideration of geological changes is made a distinct chapter1 subsequent to the one on the arrangement of materials4 ,it should1 however1 be remembered that these processes of arranging and disturbing are not thus separated in time4 ,in nature the two processes are always going on together4 ,it seemed important to exhibit the science with as much unity and completeness as possible2 and hence1 discussions upon debatable points in ,theoretical ,geology1 so interesting to mature geologists1 would have been out of place here2 and yet those more intricate subjects have not been omitted4 ,a large proportion of the work is devoted to the explanation of geological phenomena1 in order to convey an idea of the modes of investigation adopted1 and the kind of evidence relied on4 ,where diversities of opinion exist1 that view has been selected which seemed most in harmony with the facts2 and the connection has not often been interrupted to combat1 or even to state1 the antagonist view4 ,technical terms have1 in a few instances1 been introduced1 and principles referred to1 which are subsequently explained4 ,the index will1 however1 enable the student to understand them1 without a separate glossary4 ,some may prefer to commence with the second chapter1 deferring the study of the elementary substances1 minerals and rocks1 to the last4 ,such a course may be pursued without special inconvenience4 ,questions have been added1 for the convenience of those teachers who may prefer to conduct their recitations by this means4 ,but1 when the circumstances of the case admit of it1 a much more complete knowledge of the subject will be acquired by pupils who are required to analyze the sections1 and proceed with the recitation themselves2 while the teacher has only to correct misapprehension1 explain what may seem obscure1 and introduce additional illustrations4 ,,list ,,of ,,illustrations4 #a4 ,columnar ,trap1 ,new ,holland4 7,dana47 #b4 ,the four divisions of rocks1 and their relative positions4 ,a1 ,volcanic ,rocks4 ,b1 ,granite4 #a1 #b1 #c1 #d1 ,granite of different ages4 ,c1 ,metamorphic ,rocks4 ,d1 ,fossiliferous ,rocks4 7,lyell47 #c4 ,granite veins in slate1 ,cape of ,good ,hope4 7,hall47 #d4 ,granite veins traversing granite4 7,hitchcock47 #e4 ,extinct volcanoes of ,auvergne4 7,scrope47 #f4 ,lava of different ages1 ,auvergne4 7,lyell47 #g4 ,strata folded and compressed by upheaval of granite4 #h4 ,favosites ,gothlandica4 #i4 ,catenipora escharoides4 7,chain coral47 #aj4 ,caryocrinus ornatus4 7,hall47 ,leptna alternate4 ,orthis testudinaria4 #aa4 7,hall47 ,delthyris ,niagarensis4 #ab4 ,section of a chambered shell1 showing the chambers and the siphuncle4 #ac4 ,orthoceras4 #ad4 ,curved ,cephalopoda1 a1 ,ammonite2 b1 ,crioceras2 c1 ,scaphite2 d1 ,ancyloceras2 e1 ,hamite2 f1 ,baculite2 g1 ,turrilite4 7,agassiz and ,gould47 #ae4 ,trilobite4 #af4 ,cephalaspis ,lyellii4 7,agassiz47 #ag4 ,pterichthys oblongus4 7,agassiz47 #ah4 ,fault in the coal formation1 a a1 layers of coal1 b b1 surface and soil4 #ai4 ,stigmaria ficoides2 ,newcastle4 7,lindley and ,hutton47 #bj4 ,trunk of sigillaria4 7,trimmer47 #ba4 ,bark of sigillaria4 7,natural size47 #bb4 ,sphenopteris crenata4 7,lindley47 #bc4 ,pachypteris lanceolata4 7,brongn47 #bd4 ,sigillaria levigata4 7,brongn47 #be4 ,lepidodendron ,sternbergii1 ,bohemia4 7,sternberg47 #bf4 ,calamite4 #bg4 ,heterocercal fish4 ,homocercal fish4 #bh4 ,impressions of ,raindrops1 ,wethersfield1 ,conn4 7,hitchcock47 #bi4 b1 ,bird tracks in the ,conn4 ,river ,sandstone1 a1 ,consecutive tracks2 c1 ,track of ,cheirotherium 7probably a reptile71 ,penn4 and ,germany4 #cj4 ,section in the ,isle of ,portland4 7,buckland47 #ca4 ,apiocrinites rotundus1 ,bradford1 ,eng4 7,miller47 #cb4 ,gryphea incurva4 #cc4 a1 ,outline of ,ichthyosaurus2 b1 ,plesiosaurus4 #cd4 ,pterodactyle4 #ce4 a1 ,diploctenium cordatum2 b1 ,marsupites2 c1 ,salenia2 d1 ,galerites2 e1 ,micraster cor-anguinum4 7,agassiz ,gould47 #cf4 b1 ,belemnite4 a1 ,restored outline of the animal to which it belonged4 #cg4 ,cerithium intermedium4 #ch4 ,murex alveolatus4 #ci4 ,conus concinnus4 #dj4 ,nummulite4 #da4 ,outline of paleotherium4 #db4 ,outline of anoplotherium4 #dc4 ,skeleton of the mastodon4 #dd4 ,univalve with entire mouth4 #de4 ,univalve with notched mouth4 #df4 ,unimuscular bivalve4 #dg4 ,bimuscular bivalve4 #dh4 ,parallel planes of cleavage intersecting curved strata4 7,sedgwick47 #di4 a b1 ,a vein of segregation2 c d1 ,a dike4 #ej4 ,faults and denuded strata4 #ea4 ,vertical conglomerate4 7,lyell47 #eb4 ,inclined strata in ,dorsetshire1 ,england4 7,buckland47 #ec4 ,dip of strata4 #ed4 ,axes and valleys in disturbed strata4 #ee4 ,curved strata of slate1 ,berwickshire1 ,eng4 7,lyell47 #ef4 ,folded strata4 #eg4 ,slope of mountains4 #eh4 ,europe at the ,silurian epoch4 7,guyot47 #ei4 ,europe at the tertiary epoch4 #fj4 ,area of elevation and depression in the ,pacific and ,indian ,oceans4 7,darwin47 #fa4 c c1 ,coral wall4 7,trimmer47 #fb4 c c1 ,coral wall above the sea-level2 c' c'1 ,second coral wall4 #fc4 ,coral wall after partial subsidence4 #fd4 ,atoll4 ,the coral wall only appearing4 ,the original island entirely submerged4 #fe4 ,remains of the temple of ,jupiter ,serapis1 near ,naples4 #ff4 ,detached hills of old red sandstone1 ,rosshire1 ,scotland4 7,lyell47 #fg4 ,section of denuded strata1 ,mass4 7,hitchcock47 #fh4 ,grooved and striated surface of rocks4 #fi4 ,artesian wells4 #gj4 ,segregated masses in rocks4 #ga4 ,columnar form taken by basalt on solidification4 #gb4 ,layers of limestone now forming1 ,san ,vignone1 ,italy4 7,lyell47 #gc4 ,erosion of rock by the action of the waves4 #gd4 ,marine currents4 #ge4 ,sediment deposited in horizontal layers4 #gf4 ,section of greensand1 ,bedfordshire1 ,eng4 7,lyell47 #gg4 ,glacier1 with lateral and medial moraines1 a a1 ,terminal moraines4 #gh4 ,iceberg4 #gi4 ,volcanic ,eruption4 7,trimmer47 #hj4 ,fractures produced by upheaval4 #ha4 ,fossiliferous rock altered by contact with granite4 #hb4 ,consecutive changes by which horizontal strata become vertical4 ,,table ,,of ,,contents4 ,page ,,chapter ,i4 ,,of ,,the ,,material ,,which ,,compose ,,the ,,crust ,,of ,,the ,,earth4 ,,section ,i4--,,elementary ,,substances1 #aa ,,section ,,ii4--,,simple ,,minerals1 #ac ,,section ,,iii4--,,the ,,mineral ,,masses ,,which ,,form ,,the ,,crust ,,of ,,the ,,earth1 #af ,,chapter ,,ii4 ,,of ,,the ,,arrangement ,,of ,,the ,,materials ,,which ,,compose ,,the ,,crust ,,of ,,the ,,earth4 ,,section ,i4--,,the ,,classification ,,of ,,rocks1 #ba ,,section ,,ii4--,,the ,,plutonic ,,rocks1 #bc ,,section ,,iii4--,,the ,,volcanic ,,rocks1 #be ,,section ,,iv4--,,the ,,non-,,fossiliferous ,,stratified 7,,or ,,metamorphic7 ,,rocks1 #cj ,,section ,v4--,,the ,,fossiliferous ,,rocks1 #cb ,,section ,,vi4--,,fossils1 #eg ,,section ,,vii4--,,the ,,time ,,necessary ,,for ,,the ,,formation ,,of ,,the ,,stratified ,,rocks1 #fc ,,chapter ,,iii4 ,,of ,,the ,,changes ,,to ,,which ,,the ,,crust ,,of ,,the ,,earth ,,has ,,been ,,subjected4 ,,section ,i4--,,changes ,,which ,,have ,,taken ,,place ,,at ,,great ,,depths ,,below ,,the ,,surface1 #fg ,,section ,,ii4--,,changes ,,in ,,the ,,mass ,,of ,,the ,,stratified ,,rocks1 #fh ,,section ,,iii4--,,changes ,,of ,,elevation ,,and ,,subsidence1 #gc ,,section ,,iv4--,,changes ,,on ,,the ,,surface ,,of ,,the ,,earth1 #he ,,section ,v4--,,changes ,,of ,,climate1 #hh ,,section ,,vi4--,,advantages ,,resulting ,,from ,,geological ,,changes1 #ia ,,chapter ,,iv4 ,,of ,,the ,,causes ,,of ,,geological ,,phenomena4 ,,section ,i4--,,atmospheric ,,causes1 #ie ,,section ,,ii4--,,chemical ,,action1 #ig ,,section ,,iii4--,,organic ,,causes1 #aja ,,section ,,iv4--,,aqueous ,,causes1 #ajc ,,section ,v4--,,aqueo-,,glacial ,,action1 #abj ,,section ,,vi4--,,igneous ,,causes1 #abg ,,chapter ,i4 ,,of ,,the ,,materials ,,which ,,compose ,,the ,,crust ,,of ,,the ,,earth4 ,,section ,i4--,,elementary ,,substances4 ,there are about sixty substances known to the chemist which are considered as elementary2 but most of them are rarely met with1 and only in minute quantities4 ,a few of them are1 however1 so abundant1 in the composition of the crust of the earth1 as to render some attention to them necessary4 ,oxygen is more widely diffused than any other substance4 ,it is an ingredient of water and of the atmosphere1 the former containing eighty-eight per cent41 and the latter twenty-one4 ,nearly all rocks contain oxygen in combination with the metallic and metalloid bases1 and the average proportion of oxygen which they contain is about forty-five per cent42 so that it will not differ much from the truth to consider the oxygen in the earth's crust as equal in weight to all the other substances which enter into its composition4 ,hydrogen occurs in nature principally in combination with oxygen1 forming water4 ,it is also an ingredient in bitumen and bituminous coal4 ,nitrogen is confined almost entirely to the atmosphere1 of which it forms four-fifths4 ,it enters into the composition of some varieties of coal1 and is sparingly diffused in most fossiliferous rocks4 ,one of the most important substances in nature is carbon4 ,it constitutes the principal part of all the varieties of coal1 as well as of graphite1 peat and bituminous matter4 ,a much larger amount of carbon exists in the carbonic acid which is combined with the oxides of the metalloids and metals4 ,the most abundant of these compounds is limestone1 which contains about twelve per cent1 of carbon4 ,in the neighborhood of volcanoes sulphur is found pure and in a crystalline form4 ,it is a constant ingredient in volcanic rocks1 and in several of the most important ores1 particularly those of lead1 copper and iron4 ,the most abundant sulphate is gypsum1 which contains twenty-six per cent1 of sulphur4 ,in small quantities it is widely diffused in rocks1 and in the waters of the ocean4 ,chlorine is found principally as an ingredient of rock-salt1 which contains sixty per cent1 of it1 and of sea-water1 which contains one and a half per cent4 ,fluorine is found1 though very sparingly1 in nearly all the unstratified rocks4 ,it forms nearly half of the mineral known as ,derbyshire spar4 ,of the metals1 ,iron is the only one that is found abundantly4 ,it enters into the composition of nearly all mineral substances4 ,it is generally combined with oxygen1 and occurs less frequently as a carbonate or sulphuret4 ,of volcanic rocks it forms about twenty per cent4 ,its ores are sometimes found in the form of dikes or seams1 having been injected from below2 at other times1 in the form of nodules or stratified masses1 like other rocks of mechanical origin4 ,manganese is likewise extensively diffused1 but in very small quantity4 ,the other metals are often met with1 but their localities are of very limited extent4 ,of the metallic bases of the earths and alkalies1 ,silicium is the most abundant4 ,it generally occurs in the form of silex1 which is an oxide of the metal4 ,there are but few rocks in which it is not found in considerable amount4 ,aluminium generally occurs as an oxide1 in which form it is alumina4 ,it is the base of the different varieties of clay and clay-slate4 ,it is also a constituent of felspar and mica4 ,potassium is an ingredient of felspar and mica1 and hence is found in all the primary and in most of the volcanic rocks1 as well as in the stratified rocks derived from them4 ,sodium is a constituent of a variety of felspar which is somewhat abundant in volcanic rocks4 ,its principal source is the extensive beds of rock-salt1 and the same substance in a state of solution in the waters of the ocean4 ,calcium constitutes about forty per cent1 of limestone1 and is an ingredient in nearly all igneous rocks4 ,this metal1 in the state of an oxide1 is lime4 ,magnesium is somewhat abundant1 but less so than calcium4 ,it is one of the bases of dolomite and magnesian limestone1 and is an ingredient of talc and all talcose rocks4 ,the substances now enumerated constitute nearly the entire mineral mass of the crust of the earth4 ,they may be arranged in the following order3-- ,i4 ,,non-,,metallic ,,substances4 ,oxygen4 ,hydrogen4 ,nitrogen4 ,carbon4 ,sulphur4 ,chlorine4 ,fluorine4 ,,ii4 ,,metals4 ,iron4 ,manganese4 ,,iii4 ,,metallic ,,bases ,,of ,,the ,,earths ,,and ,,alkalies4 ,silicium4 ,aluminium4 ,potassium4 ,sodium4 ,calcium4 ,magnesium4 ,these substances1 chemically combined1 form ,simple ,minerals4 ,,section ,,ii4--,,simple ,,minerals4 ,all substances found in the earth or upon its surface1 which are not the products of art or of organic life1 are regarded by the mineralogist as simple minerals4 ,about four hundred mineral species are known1 and the varieties are much more numerous2 but only a small number of them are so abundant as to claim the attention of the geologist4 ,an acquaintance with the following species is1 however1 necessary4 ,quartz is probably the most abundant mineral in nature4 ,it is composed wholly of silex4 ,its specific gravity is #b4fe4 ,it is the hardest of the common minerals1 gives sparks with steel1 scratches glass1 and breaks into irregular angular fragments under the hammer4 ,when crystallized1 its most common form is that of a six-sided prism1 terminated by six-sided pyramids4 ,when pure1 it is transparent or translucent1 and its lustre is highly vitreous4 ,the transparent variety is called rock crystal4 ,when purple1 it is amethyst4 ,when faint red1 it is rose quartz4 ,when its color is dark brown1 or gray1 and it has a conchoidal fracture1 it is flint4 ,when quartz occurs in white1 tuberous masses1 of a resinous lustre and conchoidal fracture1 it is opal4 ,the precious opal is distinguished by its lively play of colors4 ,jasper is opaque1 and contains a small per cent1 of oxide of iron1 by which it is colored dull red1 yellowish red or brown4 ,the light-colored1 massive1 translucent variety is chalcedony4 ,the flesh-colored specimens are carnelian4 ,when composed of layers of chalcedony of different colors1 it becomes agate4 ,several of the varieties of quartz1 such as amethyst1 opal1 carnelian and agate1 are used to considerable extent in jewelry4 ,felspar is composed of silex1 alumina and potassa4 ,it resembles quartz1 but it is not as hard1 cleaves more readily1 and is not generally transparent4 ,its specific gravity is #b4dg4 ,its lustre is feebly vitreous1 but pearly on its cleavage faces4 ,its color is sometimes green1 but generally dull white1 and often inclined to red or flesh-color4 ,mica is composed of the same ingredients as felspar1 together with oxide of iron4 ,its specific gravity is nearly three4 ,it is often colorless1 but frequently green1 smoky1 or black4 ,it may be known by its capability of division into exceedingly thin1 transparent1 elastic plates4 ,hornblende is composed of silex1 alumina and magnesia4 ,its specific gravity is a little above three4 ,its color is generally some shade of green4 ,when dark green or black1 whether in a massive or crystalline state1 it is common hornblende4 ,when light green1 it is actinolite4 ,the white variety is tremolite4 ,when it is composed of flexible fibres1 it is asbestus2 and when the fibres have also a silky lustre1 it is amianthus4 ,augite or ,pyroxene has1 till recently1 been considered as a variety of hornblende4 ,its specific gravity is slightly different2 its composition is the same1 and in general appearance it is not easily distinguished from hornblende4 ,it has1 however1 been made a distinct species1 because its crystalline form is different4 ,hypersthene is composed of silex1 magnesia and oxide of iron4 ,its specific gravity is #c4ch4 ,it closely resembles hornblende4 ,the lustre of its cleavage faces is metallic pearly4 ,its color is grayish or greenish black4 ,talc is composed of silex and magnesia4 ,its specific gravity is #b4g4 ,it resembles mica in its general appearance and in its lamellar structure1 but it is easily distinguished from it by its plates being not elastic1 and by its soapy feel4 ,its color is generally some shade of green4 ,soapstone is an impure variety of talc1 of a light gray color1 earthy texture1 and is unctuous to the touch4 ,chlorite1 another impure variety1 is a dark green rock1 massive1 easily cut with a knife1 and unctuous to the touch4 ,serpentine is composed of silex and magnesia4 ,its specific gravity is #b4ee4 ,it is generally massive1 unctuous to the touch1 and of a green color4 ,it is often variegated with spots of green of different shades4 ,with a mixture of carbonate of lime it forms the verd antique marble4 ,carbonate of ,lime1 or common limestone1 is composed of carbonic acid and lime4 ,its specific gravity is #b4fe4 ,it presents a great variety of forms4 ,in a crystalline state it is generally transparent1 and when so1 possesses the property of double refraction4 ,it may be distinguished from every other common species by its rapid effervescence with acids4 ,it readily cleaves parallel to all the faces of the primary form1 which is a rhombohedron4 ,sulphate of ,lime1 or ,gypsum1 is composed of sulphuric acid and lime4 ,its specific gravity is #b4cb4 ,when crystalline1 it has a pearly lustre1 is transparent1 and goes under the name of ,selenite4 ,common ,gypsum resembles the other earthy limestones1 but it is softer1 and may be readily distinguished by its not effervescing with acids4 ,to the minerals now enumerated may be added the following1 which are of frequent occurrence1 but not in great quantities2 namely1 carbonate of magnesia1 oxide of iron1 iron pyrites1 rock-salt1 coal1 bitumen1 schorl and garnet4 ,these simple minerals1 either in separate masses or mingled more or less intimately together1 compose almost wholly the earth's crust4 ,,section ,,iii4--,,the ,,mineral ,,masses ,,which ,,form ,,the ,,crust ,,of ,,the ,,earth4 ,that portion of the structure of the earth which is accessible to man is called the crust of the earth4 ,the mineral masses which compose it1 whether in a solid state1 like granite and limestone1 or in a yielding state1 like beds of sand and clay1 are called rocks4 ,the unstratified rocks are ,granite1 ,hypersthene rock1 ,limestone and ,serpentine1 and the ,trappean and ,volcanic rocks4 ,granite is a rock of a light gray color1 and is composed of quartz1 felspar and mica1 in variable proportions1 confusedly crystallized together4 ,the felspar is generally the predominant mineral4 ,it is sometimes of a very coarse texture1 the separate minerals occurring in masses of a foot or more in diameter4 ,at other times it is so fine-grained that the constituent minerals can scarcely be recognized by the naked eye2 and between these extremes there is every variety4 ,the term granite is not1 however1 confined to an aggregate of these three minerals4 ,in some instances the felspar so predominates as almost to exclude the other minerals1 when it is called felspathic granite4 ,when the quartz appears in the form of irregular and broken lines1 somewhat resembling written characters1 in a base of felspar1 it is called graphic granite4 ,when talc takes the place of mica1 it is talcose granite4 ,when hornblende takes the place of mica1 it is syenite4 ,granite or any rock becomes porphyritic when it contains imbedded crystals of felspar4 ,there is a rock of crystalline structure1 like granite1 but of a darker color1 which is called hypersthene rock4 ,it is composed of ,labrador felspar and hypersthene4 ,the mineral species serpentine and limestone often occur unstratified in considerable quantities4 ,volcanic rocks consist of the materials ejected from the craters of volcanoes4 ,they are composed of essentially the same minerals as trap rocks4 ,when the material has been thrown out in a melted state1 it is called lava4 ,lava1 at the time of its ejection1 contains a large amount of watery vapor at a high temperature4 ,under the immense pressure to which it is subjected in the volcanic foci1 it may exist in the form of water2 but when the lava is thrown out at the crater1 the pressure cannot much exceed that of the atmosphere4 ,the particles of water at once assume the gaseous form4 ,as lava possesses considerable viscidity1 the steam does not escape1 but renders the upper portion of the mass vesicular4 ,this vesicular lava is called scori4 ,by the movement of the stream of lava1 these vesicles become drawn out into fine capillary tubes1 converting the scori into pumice-stone4 ,a large part of the materials ejected from volcanoes is in the form of dust1 cinders and angular fragments of rock4 ,these soon become solidified1 forming volcanic tuff1 or volcanic breccia4 ,in submarine eruptions these fragments are spread out by the water into strata1 upon which other materials1 not volcanic1 are afterwards deposited4 ,these interposed strata are called volcanic grits4 ,the trappean rocks are composed of felspar1 mingled intimately and in small particles with augite or hornblende4 ,they also contain iron and potassa4 ,they are often porphyritic4 ,when they contain spherical cavities1 filled with some other mineral1 such as chlorite1 carbonate of lime or agate1 they are called amygdaloidal trap4 ,the principal varieties of trappean rock are basalt1 green stone1 and trachyte4 ,in basalt1 augite1 or1 in some cases1 hornblende1 is the predominant mineral4 ,it is a heavy1 close-grained rock1 of a black or dark brown color4 ,greenstone differs from basalt in containing a much larger proportion of felspar4 ,its structure is more granular1 and frequently it assumes so much of the crystalline form as to pass insensibly into syenite or granite4 ,it is a dark colored rock1 with a slight tinge of green4 ,both green stone and basalt are disposed to assume the columnar form1 the columns being arranged at right angles to the faces of the fissure into which the trap is injected4 ,when it is spread out into broad horizontal masses1 the columns are vertical4 7,fig4 #a47 ,trachyte is composed principally of felspar1 is of a grayish color1 and rough to the touch4 ,illustration3 ,fig4 #a4 ,of the stratified rocks the following are the most important3 ,gneiss is a rock closely resembling granite4 ,it is an aggregate of the same minerals1 but the proportion of mica is somewhat greater4 ,the only distinction between them is that the gneiss is stratified1 but the stratification is often so indistinct that it passes insensibly into granite4 ,generally1 however1 the stratification is so distinct as to present a marked difference4 ,mica slate is such a modification of gneiss that the mica becomes the predominant mineral1 with a small intermixture of quartz and felspar4 ,consequently the stratification becomes very distinct1 so as sometimes to render the mass divisible into thin sheets4 ,the stratification is often wavy1 and sometimes much contorted4 ,sandstone consists of grains or fragments of any other rock1 but more frequently of siliceous rocks4 ,the fragments are consolidated1 sometimes without any visible cement1 but often by a paste of argillaceous or calcareous substance4 ,the color varies with that of the rock from which it was derived4 ,generally1 however1 it is either drab or is colored red by oxide of iron4 ,the fragments are sometimes so minute as scarcely to give the rock the appearance of sandstone4 ,when they are of considerable size and rounded1 the rock is called conglomerate4 ,when they are angular1 it is called breccia4 ,greensand is a friable mixture of siliceous and calcareous particles1 colored by a slight intermixture of green earth or chlorite4 ,limestone is a very abundant rock1 and occurs in many different forms4 ,in transparent crystals it is ,iceland spar4 ,when white and crystalline1 it is primary limestone1 saccharine limestone1 or statuary marble4 ,when sub-crystalline it is generally more or less colored4 ,it is often clouded with bands or patches of white in a ground of some dark color4 ,when its texture is close1 and the crystallization scarcely apparent1 it is compact limestone4 ,the white1 earthy variety is chalk4 ,a variety of limestone composed of small spheres is called olite4 ,lias is the name given to an impure argillaceous variety of a brown or blue color4 ,any rock which contains a considerable proportion of carbonate of lime1 and which rapidly disintegrates on exposure to the atmosphere1 is called marl4 ,limestone sometimes contains carbonate of magnesia4 ,it is then magnesian limestone1 or dolomite4 ,clay consists of a mixture of siliceous and aluminous earth4 ,it is tough1 highly plastic1 and generally of a lead blue color4 ,it is always stratified1 and often divided into very thin lamin1 which are separated by sprinklings of sand only sufficient to keep them distinct4 ,clay slate1 or argillaceous schist1 is composed of the same materials as clay1 and differs from it only in having become solidified4 ,its color is gray1 dark brown or black4 ,in some beds it is purple4 ,shale is the same material in a state of partial solidification4 ,on exposure to the weather1 it soon disintegrates1 and is finally reconverted into clay4 ,all the varieties of argillaceous rock are easily distinguished by a peculiar odor which they emit when breathed upon4 ,argillaceous slate sometimes takes into its composition portions of some other mineral1 such as talc1 mica1 or hornblende4 ,when any of these minerals becomes so abundant as to constitute a considerable part of the mass1 the rock becomes talcose1 micaceous1 or hornblende slate4 ,sometimes this last variety loses all appearance of a fissile structure1 and is composed almost wholly of hornblende4 ,it is then called hornblende rock4 ,diluvium is the name applied to masses of sand1 gravel1 and large rocks1 called boulders1 heaped confusedly together on the surface of the earth4 ,it is also called drift4 ,,chapter ,,ii4 ,,of ,,the ,,arrangement ,,of ,,the ,,materials ,,which ,,compose ,,the ,,crust ,,of ,,the ,,earth4 ,,section ,i4--,,the ,,classification ,,of ,,rocks4 ,in the first place1 we divide rocks into stratified and unstratified4 ,this division is one which will in general be easily recognized1 even by the most inexperienced observer2 and the distinction is important1 because it separates the rocks of igneous origin from those which have been produced by deposition of sediment from water4 ,it will be shown hereafter that a part of the unstratified rocks have been formed at or near the surface of the earth2 that is1 they have taken their present form by passing from a state of fusion to a solid state above or between the stratified rocks1 as in the case of lava 7,fig4 #b1 ,a74 ,the other unstratified rocks have cooled so as to take the solid form below the stratified rocks1 as at ,b4 ,the first are called epigene1 or volcanic rocks2 the last1 hypogene1 or plutonic rocks4 ,the lowest portion of the second division1 the stratified rocks1 are termed non-fossiliferous1 from the fact that they contain no evidence of the existence of organic beings at the time when they were deposited4 ,their relation to the other rocks is shown at ,c4 ,it is supposed that these rocks have been subjected to great changes by heat from the igneous rocks below them4 ,on this account ,mr4 ,lyell proposes to call them metamorphic rocks4 ,the other portions of the stratified rocks are fossiliferous1 containing the remains of organic beings which lived at the period when the rocks were deposited4 ,they are represented at ,d4 ,the division of the last-named rocks info groups will be given hereafter4 ,illustration3 ,fig4 #b4 ,we have then four principal classes of rocks3 ,plutonic ,rocks1 ,volcanic ,rocks1 ,non-fossiliferous ,stratified ,rocks and ,fossiliferous ,rocks4 ,,section ,,ii4--,,the ,,plutonic ,,rocks4 ,granite is by far the most important of this class of rocks4 ,of its thickness no estimate can be made1 as no mining operations have ever penetrated through it1 and none of the most extensive displacements of rocks by natural causes has brought to the surface any other rock on which it rests4 ,it may1 therefore1 be considered the foundation rock1 the skeleton of the earth1 upon which all the other formations are supported4 ,the whole amount of granite in the earth's crust may be greater than that of all other rocks1 but it comes up through the other formations so as to be exposed over only a comparatively small portion of the surface1 and this is generally the central portion of mountain ranges1 or the highest parts of broken1 hill country4 ,still1 it is not unfrequently found in the more level regions1 in the form of slightly elevated ridges1 with the stratified rocks reclining against it4 ,the structure of granite seems frequently to be a confused mixture of the minerals which compose it1 without any approach to order in their arrangement2 but in many cases it is found to split freely in certain directions1 and to work with difficulty in any other4 ,this may result from an arrangement of the integrant crystals1 so that their cleavage planes approach more or less nearly to parallelism4 ,when this is the case with the mica or felspar1 it must diminish the cohesion in a direction perpendicular to these planes1 and thus facilitate the cleavage of the mass4 ,illustration3 ,fig4 #c4 ,granite is found to penetrate the stratified rocks in the form of veins4 ,the following section 7,fig4 #c7 will show the relation of granite veins to the granitic mass below4 ,the granite which is quarried for architectural purposes is often in comparatively small quantities1 disappearing at the distance of a few hundred yards beneath the stratified rock2 or else it exists in the form of isolated dome-shaped masses4 ,it is probable that1 if they could be followed sufficiently far1 they would be found to be portions of dikes coming from the general mass of granite below4 ,even the granite nuclei of the great mountain ranges may be considered as injected dikes of enormous magnitude4 ,illustration3 ,fig4 #d4 ,granite is itself intersected with granite veins more frequently1 perhaps1 than any other rocks2 but the vein is a coarser granite than the rock which it divides4 ,it is not uncommon to find one set of dikes intercepted and cut off by a second set1 and the second by a third4 ,the substance of the dikes was1 of course1 in a liquid state when it was injected1 and the first must have become solid before the second was thrown in2 hence the dikes are of different ages4 ,the dikes a b c1 represented in ,fig4 #d1 must have been injected in the order in which they are lettered4 ,it is probable that1 by the process of cooling1 the liquid mass from which these dikes have proceeded has been gradually solidifying from the surface downwards4 ,if so1 it would follow that the granite nearest the surface 7#a1 ,fig4 #b7 is the oldest1 and the newest is that which is at the greatest distance below 7#d74 ,it is possible that at great depths granite may be still forming1 that is1 taking the solid form1 though of this there can be no direct proof4 ,there is1 however1 proof that it has been liquid at periods of time very distant from each other2 for the dikes sometimes reach to the top of the coal formation 7for example71 and then spread themselves out horizontally1 as at a1 showing that the rock above the coal had not then been deposited4 ,another dike will extend through the new red sandstone1 as at b1 and spread itself out horizontally as before4 ,these horizontal layers of granite1 by their position in strata whose ages are known1 indicate the periods when granite has existed in a liquid state4 ,granite veins have been discovered in the ,pyrenees as recent as the close of the cretaceous period1 and in the ,andes they have been found among the tertiary rocks4 ,there are several other rocks1 of minor importance1 often found in connection with granite4 ,hypersthene rock1 in a few cases1 forms the principal part of mountain masses4 ,greenstone is more frequently associated with the trappean rocks1 but it sometimes passes imperceptibly into syenite and common granite4 ,limestone is found in considerable abundance1 and serpentine in small quantities1 as primary rocks1 and have evidently been formed like granite1 by solidifying from a state of fusion4 ,,section ,,iii4--,,the ,,volcanic ,,rocks4 ,the volcanic rocks consist of materials ejected from volcanoes4 ,they are1 however1 ejected in very different states2 sometimes as dust1 sand1 angular fragments of rock1 cinders1 c41 and sometimes as lava streams4 ,in some instances1 the lava has so little fluidity that it accumulates in a dome-shaped mass over the orifice of eruption1 and perhaps in a few instances it has been thrust upward in a solid state4 ,there are two principal varieties of lava1 the trachytic1 consisting mostly of felspar1 and the basaltic1 consisting of hornblende4 ,when both kinds are products of the same eruption1 the trachytic lava is thrown out first1 and the basaltic last4 ,the reason of this is1 that felspar is lighter than hornblende1 and probably rises to the surface of the lava mass at the volcanic focus1 and the basaltic lava is therefore reserved till the trachytic has been thrown off4 ,these1 like other rocks1 have been produced at different epochs4 ,there is1 however1 great difficulty in determining their age2 ,there are some differences of structure and composition observed1 in comparing the older and newer lavas2 but the only method that can be relied on to determine their age is their relation to other rocks4 ,when they occur between strata whose age is determined by imbedded fossils1 they must be of intermediate age between the inferior and superior strata4 #a4 ,modern ,volcanic ,rocks4--,some of the volcanic rocks are of modern origin1 and are produced by volcanoes now active4 ,the total amount of these1 and of all the other volcanic rocks1 is probably less than that of either of the other principal divisions of rocks2 yet they form no inconsiderable part of the earth's crust4 ,the number of active volcanoes is not far from three hundred1 and the number of eruptions annually is estimated at about twenty4 ,in some cases1 the lava consists of only a single stream1 of but a few hundred yards in extent4 ,it extends1 however1 not unfrequently twenty miles in length1 and two or three hundred yards in breadth4 ,the eruption of ,mount ,loa1 on the island of ,hawaii1 in #ahdj1 from the crater of ,kilauea1 covered an area of fifteen square miles to the depth of twelve feet2 and another eruption of the same mountain1 in #ahdc1 covered an area of at least fifty square miles4 ,the eruption in ,iceland1 in #aghc1 continued in almost incessant activity for a year1 and sent off two streams in opposite directions1 which reached a distance of fifty miles in one case1 and of forty in the other1 with a width varying from three to fifteen miles1 and with an average depth of more than a hundred feet4 ,the size of some of the volcanic mountains will also assist in forming an idea of the amount of volcanic rocks4 ,monte ,nuovo1 near ,naples1 which is a mile and a half in circumference and four hundred and forty feet high1 was thrown up in a single day4 tna1 which is eleven thousand feet high1 and eighty-seven miles in circumference at its base1 has probably been produced wholly by its own eruptions4 ,a large part of the chain of the ,andes consists of volcanic rock1 but the proportion we have not the means of estimating4 #b4 ,tertiary ,lavas4--,there is another class of volcanic products1 which are so situated with reference to the tertiary strata that they must be referred to that period4 ,the principal localities of these lavas1 so far as yet known1 are ,italy1 ,spain1 ,central ,france1 ,hungary1 and ,germany4 ,they are also found in ,south ,america4 ,those of ,central ,france have been studied with the most care4 ,they occur in several groups1 but they were the seats of volcanic activity during the same epoch1 and formed parts of one extensive volcanic region4 ,each of these minor areas1 embracing a circle of twenty or thirty miles in diameter1 is covered with hills two or three thousand feet in height1 which are composed entirely of volcanic products1 like the cone of tna4 ,on many of them there are perfectly-formed craters still remaining4 ,numerous streams of lava have flowed from these craters1 some of which can now be traced1 throughout their whole extent1 with as much certainty as if they were eruptions of the present century4 ,some of the lavas have accumulated around the orifices of eruption1 forming rounded1 dome-shaped eminences4 ,these lavas generally consist of trachyte1 and have therefore a low specific gravity1 and imperfect fluidity4 ,the basaltic lavas have often spread out over broad areas1 and1 when they have been confined in valleys1 have reached a distance of fifteen miles or more from their source4 ,there still remain indications of a current of lava which was thirty miles long1 six broad1 and in a part of its course from four to six hundred feet deep4 ,the above sketch 7,fig4 #e7 will give some idea of the highly volcanic aspect which the district of ,auvergne1 in ,france1 presents4 ,illustration3 ,fig4 #e4 ,the unimpaired state of some of the cones and craters1 and of the lava currents1 would lead to the impression that these regions have been the theatre of intense volcanic action within a very recent period4 ,but there is good reason to believe that this has not been the case4 ,the high antiquity of the most modern of these volcanoes is indeed sufficiently obvious4 ,had any of them been in a state of activity in the age of ,julius ,csar1 that general1 who encamped upon the plains of ,auvergne and laid siege to its principal city1 could hardly have failed to notice them4 ,it is equally certain that the commencement of their activity was at a late period in the history of the earth4 ,lava currents are frequently found in ,france resting upon the early tertiary strata1 but no lava current is found below them4 ,the later tertiary strata contain pebbles of volcanic rocks1 showing that lavas had been previously ejected1 but none are found in the older strata of this formation4 ,we must1 therefore1 conclude that these volcanic tracts assumed their volcanic character at some intermediate point in the tertiary period4 ,when we find that their activity commenced at so late a period and closed so long ago1 we might be led to suppose that it was of very short duration4 ,but a great number of facts1 in the present condition of the country1 require that we should assign to them a very prolonged activity4 ,a single instance will be sufficient to show the nature of the evidence upon which this conclusion rests4 ,the heavy line 7,fig4 #f7 represents the present form of one of the valleys4 ,a bed of lava forms the highest point of land represented1 and a second bed is found in an intermediate part of the slope4 ,the position of the upper bed must have been a valley1 when the lava flowed there4 ,we may represent this valley by the line a b c4 ,the slow operation of natural denuding causes at length excavated the valley d e h1 when another lava current flowed through it1 covering its bed of pebbles1 as before4 ,the same denuding causes have at length produced the present valley1 f g h4 ,these remnants of lava-currents1 as they have formed a very imperishable rock1 have protected the subjacent strata from erosion1 and furnish evidence of the position of the valley at different periods4 ,when we consider with what extreme slowness denuding causes produce changes on the surface1 and what extensive changes they have here nevertheless effected in the interval between the production of the different lava currents1 we are compelled to feel that that interval was a very prolonged one4 ,yet this period1 however long it may have been1 was evidently less than the period of activity of these volcanoes4 ,illustration3 ,fig4 #f4 #c4 ,volcanic rocks of an earlier date are also found1 sometimes as distinct lavas1 though generally as volcanic grits4 ,they occur interstratified with the cretaceous rocks1 and with every other formation of the fossiliferous series1 showing that1 from the earliest times1 these rocks have been accumulating as they now are4 ,the trappean rocks may1 in a general classification1 be considered as volcanic4 ,it will be shown1 hereafter1 that they are the lavas of submarine volcanoes4 ,they do not1 however1 occur in the form of lava currents1 but in great tabular masses1 generally between stratified rocks1 or in the form of dikes4 ,they are also entirely unconnected with cones or craters4 ,the trappean rocks occur more or less abundantly in all countries4 ,one of the most noted localities of this rock is a region embracing the north of ,ireland1 and several of the islands on the western coast of ,scotland4 ,it contains the celebrated ,giant's ,causeway1 which consists of a mass of columnar trap2 also ,fingal's ,cave1 which is produced by a portion of the trap being columnar1 and thus disintegrating more rapidly than the rest1 by the action of the waves4 ,an immense mass of greenstone trap1 which has generally been considered as a vast dike1 though often a mile in thickness1 is found extending from ,new ,haven to ,northampton1 on the west side of the ,connecticut river4 ,it then crosses to the east side1 and continues in a northerly direction to the ,massachusetts line4 ,under different names1 it constitutes a nearly continuous and precipitous mountain range for about one hundred miles4 ,dr4 ,hitchcock supposes this greenstone range to be1 not an injected dike1 but a tabular mass of ancient lava1 which was spread out on the bed of the ocean during the period of the deposition of the ,connecticut river sandstone4 ,it was subsequently covered with a deposit of strata of great thickness1 and then by subterranean forces thrown into its present inclined position4 ,there is a mass of basaltic rock in the valley of the ,columbia river1 in the ,oregon ,territory1 which extends without interruption for a distance of four hundred miles4 ,its breadth and thickness is not known1 but in some places the river has cut a channel in this rock to a depth of four hundred feet4 ,its age has not been determined1 and it will1 perhaps1 be found to be a tertiary or modern production4 ,,section ,,iv4--,,the ,,non-,,fossiliferous ,,stratified 7,,or ,,metamorphic7 ,,rocks4 #a4 ,gneiss is the most abundant rock in this class1 and is generally found reposing on granite4 ,its stratification is sometimes very distinct1 but it is often so imperfect that it can scarcely be recognized4 ,this is more frequently the case in the vicinity of granite on which it rests1 and into which it insensibly passes4 ,a large part of the material used for building purposes1 under the name of granite1 is obscurely marked gneiss4 ,in all primary countries it is an abundant rock1 occupying extensive districts1 and sometimes forming mountain masses4 #b4 ,mica slate lies next above gneiss1 and is a very abundant rock4 ,as it differs from gneiss only in the proportion of mica which it contains1 and as the quantity of mica in it is very different in different places1 it is often difficult to make the distinction between them4 ,it also passes by insensible degrees into the argillaceous rocks4 ,many of the argillaceous rocks are found1 upon close examination1 to contain mica in minute scales in such abundance as to make it doubtful whether they ought not to be regarded as mica slates2 that is1 the metamorphic action by which argillaceous slate is converted into mica slate had proceeded so far1 before it was arrested1 that it becomes impossible to say whether the argillaceous or micaceous characters predominate4 #c4 ,argillaceous slate4--,the last rock of this series is a slaty rock1 more or less highly argillaceous4 ,it does not differ in lithological characters from the same rock in the higher strata4 ,it is doubtful whether the roofing-slates should be considered as belonging to the metamorphic series or not4 ,they have been subjected to a very high degree of metamorphic action1 and yet strata intimately associated with them have1 in occasional instances1 contained fossils4 ,it is not easy to fix the exact upper limit of this series4 ,the fossils are few1 obscure1 and seldom met with in the lowest fossiliferous series2 and the transition is very gradual from the distinctly metamorphic to the fossiliferous rocks4 ,this renders it impossible always to determine accurately the line of separation4 ,the gneiss1 mica slate and argillaceous slate1 have the order of superposition in which they are here named4 ,they differ only in the amount of metamorphic action to which they have been subjected2 and the gneiss which is most highly metamorphic has1 by being the lowest1 been most acted upon1--the mica slate less1 and the argillaceous slate least4 ,in a particular locality1 however1 the lowest rock which was subjected to these causes of change1 instead of having been of such a character as to produce gneiss1 may have been a limestone1 and in that case the lowest metamorphic rock would be a saccharine marble4 ,in another locality the lowest rock may have been a sandstone1 which would be converted into quartz rock4 ,hence there may occur1 in any part of the metamorphic series1 crystalline limestone1 quartz rock1 hornblende slate1 chlorite slate1 and talcose slate2 and any one of these rocks may be as abundant in any particular region1 as gneiss1 mica slate or argillaceous slate1 is in another4 ,the metamorphic rocks occur in all countries where there has been any considerable amount of volcanic action1 and their total amount is very great2 but their stratification is so confused and contorted1 their superposition so irregular1 and denudations have been so extensive1 that no estimate can be made of their thickness4 ,they are1 perhaps1 equal to all the other stratified rocks4 ,,section ,v4--,,the ,,fossiliferous ,,rocks4 ,the fossiliferous rocks are divided into seven systems1 which are readily distinguished by the order of superposition1 lithological characters and organic remains4 ,these systems are the ,silurian1 the ,old ,red ,sandstone1 the ,carboniferous1 the ,new ,red ,sandstone1 the ,olitic1 the ,cretaceous1 and the ,tertiary systems4 ,there is also an eighth system now in process of formation4 ,it is the opinion of some geologists that there is another system situated between the metamorphic rocks and the silurian system4 ,it has been called by ,dr4 ,emmons1 who has studied it with much care1 the ,taconic ,system1 the ,taconic ,mountains1 in the western part of ,massachusetts1 being composed of these rocks4 ,it is the lower part of what has been called1 in ,england and ,wales1 the ,cambrian system4 ,the strata of this system have a nearly vertical position1 and consist principally of black1 greenish and purple slates1 of great thickness4 ,granular quartz rock1 however1 occurs in considerable quantity1 and in this country two thick and important beds of limestone are found4 ,these limestones are occasionally white and crystalline4 ,generally1 however1 as a mass1 they are a dark1 nearly black rock1 with a network of lines of a lighter color4 ,all the clouded marbles for architectural and ornamental purposes are from these beds1 and our roofing and writing slates are all obtained from the argillaceous portion of this system4 ,the number of species of organic remains contained in this system is very small1 and these1 so far as discovered1 belong to the annelida1 with a few doubtful cases of mollusca4 ,this system of rocks is found coming to the surface in a large part of ,new ,england1 and the eastern part of ,new ,york1 also in the western part of ,england and ,wales4 ,those geologists who deny the existence of this system consider these rocks as parts of the silurian system which have been most disturbed by subterranean forces1 and most altered by proximity to igneous rocks4 ,the annexed sketch 7,fig4 #g7 will exhibit the relations here referred to4 ,certain portions of the silurian rocks are supposed to have been thrown into folds by the upheaval of the primary rocks4 ,the plications nearest to the intrusive granite would be most altered4 ,that part of the figure below the line a a represents the outcropping edges as they now appear1 the upper portion of the folds having been removed by some abrading cause4 ,illustration3 ,fig4 #g4 ,as it is yet uncertain which of these views is correct1 convenience will justify us in retaining the name of ,cambrian system till further investigations shall settle the question4 #a4 ,the ,silurian ,system4--,the following tabular arrangement exhibits the divisions of the system as recognized in ,england1 in ,new ,york1 in ,pennsylvania and ,virginia1 and in ,ohio4 ,key to ,divisions ---------------- ,c - ,cambrian ,rocks4 ,s - ,silurian ,system4 ,d - ,devonian4 ,ch - ,champlain ,division4 ,on - ,ontario ,division4 ,he - ,helderberg ,division4 ,er - ,erie ,division4 ,divisions as recognized ,divisions as recognized ,pennsylvania ,ohio4 by ,english ,authors4 by the ,new ,york and ,virginia4 ,geologists4 _/------------------- _/----------------------- _/---------- _/-------- ,upper ,cambrian ,potsdam ,sandstone4 ,no4 #a4 ,c ,rocks1 of ,sedgwick ,calciferous ,sandrock4 ,birdseye ,limestone4 ,no4 #b4 7probably74 ,ch ,trenton ,limestone4 ,blue ,limestone ,llandeilo ,flags4 ,utica ,slate4 and ,marl4 ,no4 #c4 ,hudson ,river ,group4 ,gray ,sandstone4 ,no4 #d4 ,oneida ,conglomerate4 ,on ,caradoc ,sandstone4 ,medina ,sandstone4 ,no4 #e4 ,clinton ,group4 ,niagara ,group4 ,oneida ,salt ,group4 3 ,water-lime ,group4 3 ,pentamerus ,limestone4 ,no4 #f4 3 ,delthyris ,shaly 3 ,limestone4 3 ,s ,encrinal ,limestone4 3 ,cliff ,wenlock ,rocks4 ,he ,upper ,pentamerus 3 ,limestone4 3 ,limestone4 ,oriskany ,sandstone4 3 ,no4 #g4 3 ,cauda-,galli ,grit4 3 ,schoharie ,grit4 3 ,onondaga ,limestone4 ,wanting4 3 ,corniferous ,limestone4 ,wanting4 ,marcellus ,shales4 ,black ,hamilton ,group4 ,slate4 ,upper and ,lower ,no4 #h4 ,tully ,limestone4 ,ludlow ,rocks and ,er 3 ,genesee ,slate4 ,d 3 the ,devonian 3 ,portage ,group4 ,no4 #i4 ,waver 3 ,system4 ,chemung ,group4 ,sandstone4 ,this name1 ,silurian1 was first used to designate the lowest well-characterized fossiliferous rocks in ,england4 ,but it is now used to embrace the whole system as it occurs elsewhere4 ,it is well exhibited in ,new ,york1 both in consequence of its great development there1 and because the whole system is only slightly acted upon by disturbing forces1 so that the outcropping edge of each division extends over a large surface4 ,this system is of great thickness1 amounting1 in places where it is well developed1 to twenty thousand feet4 ,the ,champlain division commences with a quartzose sandstone1 passing gradually into limestone1 which is succeeded by a very thick argillaceous deposit1 the ,utica slate and ,hudson ,river group4 ,the ,ontario division in the lower part is a mass of sandstone4 ,above this is the ,clinton group1 consisting of shales and sandstones4 ,the most important part of this group1 in an economical point of view1 is a fossiliferous1 argillaceous iron ore1 coextensive with the group in this country1 and is worked to supply a large number of furnaces4 ,the last of the division is the ,niagara group1 which commences with a mass of shale1 and becoming at length calcareous1 it terminates in a firm compact limestone4 ,this limestone has withstood the action of denuding causes better than the shales either above or below it4 ,it therefore presents a bold escarpment at its outcrop1 and occasions waterfalls wherever streams of water cross it4 ,the falls of ,niagara are formed by this rock4 ,the ,niagara limestone1 in its extension westward1 becomes the lead-bearing rock of ,missouri1 ,iowa and ,wisconsin4 ,the ,helderberg division is a succession of highly fossiliferous limestones1 with the intervention of only occasional beds of grits and shales4 ,one member of the series is the ,onondaga ,salt group4 ,the water obtained from this group in ,new ,york annually furnishes immense quantities of salt4 ,the ,erie division consists of a thick mass of shales and sandstones4 ,illustration3 ,fig4 #h4 ,illustration3 ,fig4 #i4 ,illustration3 ,fig4 #aj4 ,the fossils of this system are very numerous1 but consist mostly of the lower forms of animal life4 ,corals 7,figs4 #h and #i7 are abundant1 and constitute in some places a large proportion of the limestones4 ,the ,crinoidea1 or lily-shaped animals1 consist of a jointed stem permanently attached1 and bearing at the free extremity of the stem an expanded portion1 which is the pelvis1 or digestive cavity4 ,the mouth is surrounded with a series of leaf-like tentacula1 which serve the purpose of seizing and holding food4 ,fig4 #aj represents the pelvis of one of the silurian fossils4 ,the general character of the animal is better represented by ,fig4 #cj4 ,the most abundant fossils of this period are the lowest orders of bivalve mollusca 7,fig4 #aa74 ,the ,cephalopoda are characterized by having the organs of locomotion attached to the head4 ,the shell of several species is peculiar in being divided into distinct cells1 or chambers 7,fig4 #ab1 b d71 perforated by a tube 7siphuncle a74 ,these fossil shells are sometimes straight1 as the ,orthoceras 7,fig4 #ac71 or curved1 as shown in the several forms of ,fig4 #ad4 ,the ,trilobite was an articulated1 crustaceous animal1 having two lines along the back dividing it into three lobes1 from which circumstance its name is derived4 ,it is found in great numbers in the ,silurian rocks 7,fig4 #ae74 ,in a few instances remains of fishes have been found1 but they by no means characterize the system4 ,illustration3 ,fig4 #aa4 ,illustration3 ,fig4 #ab4 ,illustration3 ,fig4 #ac4 ,illustration3 ,fig4 #ad4 ,illustration3 ,fig4 #ae4 ,the geographical range of this system is probably greater than that of any system of rocks above it4 ,it is found occupying a large part of the territory west of the ,alleghany ,mountains1 from ,canada1 through ,new ,york1 and the other states1 to ,alabama2 and extending westward to and beyond the ,mississippi river4 ,it occupies a large district in the west of ,england1 and is found in great force in the north and east of ,europe4 #b4 ,the ,old ,red ,sandstone4--,this formation consists almost entirely of a sandstone of a red color4 ,it admits of division into three parts1 though the characters vary in different places4 ,the lowest is a thin-bedded argillaceous sandstone1 consisting of finely levigated material1 and easily splitting into thin sheets4 ,from this circumstance it has received the name of tilestone4 ,the middle portion is composed of nodules or concretions of limestone imbedded in a paste of red sand and shale4 ,this has been called by ,english geologists1 cornstone1 and though very partially developed in some regions where the system is found1 it is yet a very persistent member4 ,the highest member of this formation is a mass of red sandstone1 often passing into a coarse conglomerate4 ,in ,england the thickness of the ,old ,red ,sandstone is not less than ten thousand feet4 ,in this country it is scarcely three thousand feet4 ,illustration3 ,fig4 #af4 ,the fossils of this system are a few shells1 a small number of vegetable species1 and in particular localities the remains of fishes in great abundance4 ,the system is characterized principally by fossils of this last kind4 ,the fishes of this system have a cartilaginous skeleton1 but are covered with plates of bone1 which were faced externally with enamel4 ,the jaws1 which consisted of solid bone1 were not covered with integument4 ,the exterior bony covering seems to have been the true skeleton1 as is1 in part1 the case with the tortoise4 ,in some of the fishes of this period there is a wing-like expansion on each side of the neck1 which has given them the name of ,pterychthis 7,fig4 #ag74 ,in others1 as the ,cephalaspis1 the plate of bone on the back is so large as to cover nearly the whole body1 and make it resemble a trilobite 7,fig4 #ah74 ,this system has an extensive geographical range4 ,in ,england1 it occupies a band of several miles in width1 extending from the ,welsh border northward through ,scotland to the ,orkney ,islands4 ,in this country1 it forms the ,catskill ,mountains1 in ,new ,york1 and extends south and west so as to underlie the coal-fields of ,pennsylvania and ,virginia4 #c4 ,the ,carboniferous ,system4--,this system consists of three parts1 distinguished by lithological and fossil characters4 ,the carboniferous limestone is a dark-colored1 compact limestone1 forming the base of the system1 and reposing on the old red sandstone4 ,its thickness is from six hundred to one thousand feet1 often with scarcely any intermixture of other rock2 but it sometimes loses its character of a limestone1 and becomes a sandstone1 or conglomerate4 ,it generally contains the ores of lead in considerable quantity1 and from this circumstance has been called metalliferous limestone4 ,in ,england it is the principal repository of these ores4 ,in the ,western ,states it is the upper portion of the lead-bearing strata4 ,illustration3 ,fig4 #ag4 ,the fossils are marine1 and very numerous4 ,corals and crinoidea are very abundant4 ,the crinoidea1 in some localities1 form so large a part of the rock as to have given to it the name of encrinal limestone4 ,the orthoceras and trilobite are found1 but become extinct with this formation4 ,several species of bivalves1 such as ,delthyris and ,leptna1 are also common4 ,next above the limestone lies the sandstone1 sometimes called millstone grit4 ,it is generally drab-colored1 but occasionally red4 ,its thickness is often equal to that of the limestone4 ,sometimes it is fine-grained and compact2 but generally it is coarse-grained1 and often passes into a conglomerate4 ,it contains but few fossils1 and those of vegetable origin4 ,the highest part of the system is the coal measures4 ,they consist of beds of sandstone1 limestone1 shale1 clay1 ironstone and coal1 occurring without much uniformity in their order of superposition4 ,the coal measures have a thickness of about three thousand feet4 ,the sandstones and limestones are not distinguishable from the sandstones and limestones in the lower part of the system4 ,the ironstone either occurs in concretionary nodules1 often formed around some organic nucleus1 or it is an argillaceous ore1 having a slaty structure4 ,in either case1 it consists of subordinate beds in the shale4 ,the coal consists of several beds distributed through the measures4 ,the beds vary in thickness from a few lines or inches to several feet4 ,in a few cases beds have been found measuring fifty or sixty feet in thickness4 ,the workable beds are ordinarily from three to six feet thick4 ,illustration3 ,fig4 #ah4 ,the carboniferous formation is very much disturbed by dikes1 faults 7,fig4 #ah2 see also ,fig4 #ej71 and other dislocations4 ,the amount of change of position in the strata1 by faults1 is very various2 frequently but a few feet4 ,in one case in ,england there is a fault of nearly a thousand feet4 ,there is a case of dislocation in ,belgium where the strata are bent into the form of the letter ,z1 so that a perpendicular shaft would cut through the same bed of coal several times4 ,the characters and order of superposition which have now been given may be regarded as the general type of the carboniferous formation4 ,there are1 however1 several important modifications4 #a4 ,beds of coal sometimes alternate with beds of millstone grit4 ,thus1 in ,scotland and in the north of ,england1 this intermediate member of the system disappears1 or1 rather1 is incorporated with the coal measures4 ,the same is true1 to considerable extent1 in this country4 #b4 ,sometimes the carboniferous limestone also disappears as a distinct member of the system1 partly by becoming arenaceous1 and partly by the intercalation of beds of coal4 ,in this last case1 the whole formation from the old to the new red sandstone becomes a series of coal measures4 ,in this country the carboniferous limestone is found very generally to underlie the coal strata4 #c4 ,the fractures and faults1 which were formerly supposed to be characteristic of the coal formation1 are seldom found in the great coal-fields of this country1 except in those of the anthracite coal of ,pennsylvania2 and even there they are much less common than in the coal-fields of ,europe4 ,there are three principal varieties of coal1 distinguished by the different proportions of bitumen which they contain4 ,the common bituminous coal kindles readily1 emits much smoke1 and throws out so much liquid bitumen that the whole soon cakes into a solid mass4 ,it contains about forty per cent1 of bitumen4 ,the second kind1 or cannel coal1 contains twenty per cent41 and inflames easily1 but does not agglutinate4 ,the stone-coal1 or anthracite1 contains scarcely any bitumen1 ignites with difficulty1 emits but little smoke1 and produces a very intense heat4 ,the bituminous varieties are always found in the least disturbed portions of the coal districts2 and the anthracite is found in the more broken and convulsed portions1 where we may suppose that the subterranean heat has been sufficient to drive off the volatile bituminous part1 and reduce it to the anthracite form4 ,hence the eastern ,pennsylvania coal-fields1 which lie near the principal axes of elevation of the ,appalachian ,mountains1 furnish only anthracite2 while the same coal-seams1 in their extension to the western part of the state1 are bituminous4 ,where coal is quarried in large quantity1 a shaft is sunk through the overlying strata to the coal-beds1 and the coal is raised to 'the surface by steam power4 ,after the coal has been quarried to some distance from the shaft1 pillars of unquarried coal are left to support the overlying strata4 ,fatal accidents have sometimes occurred by the giving away of these supports4 ,over a large part of the coal-fields of the ,united ,states it has not yet become necessary to sink shafts4 ,the quarrying is commenced at the outcrop of the coal-bed2 and1 till the cover becomes of considerable thickness1 it has been found economical to strip off the overlying rock1 rather than to work a subterranean gallery4 ,brine-springs are often found in the coal measures of sufficient strength to be used in the manufacture of salt4 ,this is now done to considerable extent in ,ohio4 ,in the valley of the ,kenhawa river1 ,kentucky1 the rocks of which belong to the carboniferous system1 the brine is nearly saturated with salt2 and in some of the borings they have even discovered beds of rock-salt of great thickness and purity4 ,there is no other part of the geological series so obviously connected with national prosperity as the coal formation4 ,while a country is new1 the forests furnish an abundant supply of fuel2 but in the course of a few years these are consumed4 ,this country will soon be principally dependent upon its coal-mines for fuel1 even for domestic purposes2 and1 in carrying on the great branches of national industry1 such as the smelting and working of iron1 and in the formation of steam for the purposes of manufacture and transportation1 we are already mainly dependent upon mineral coal4 ,a nation which does not possess an abundant supply of this mineral1 or which does not use it1 cannot long maintain a high degree of national prosperity4 ,in these inexhaustible masses of coal1 accumulated ages before the existence of the human race1 is a most obvious prospective arrangement for securing our happiness and improvement4 ,and this arrangement embraces not only the accumulation of a combustible material in such abundance1 but also its juxtaposition with an equally inexhaustible accumulation of iron ore1 and the limestone which is necessary as a flux in the reduction of the ore4 ,so bulky and heavy materials as coal and iron ore could neither of them have been transported to any considerable distance for the manufacture of iron2 and without the manufacture of iron on a large scale1 the present operations in manufactures and transportation could never have been entered upon4 ,a large proportion of the iron furnaces in this country1 and nearly all of them in ,great ,britain1 employ mineral coal for fuel1 and obtain their ore from the beds contained in the coal measures4 ,the fossils of the coal measures are almost entirely of vegetable origin1 and are very abundant4 ,they are seldom found in the coal-beds1 but in the strata of shale immediately above or below the solid coal4 ,illustration3 ,fig4 #ai4 ,the ,stigmaria 7,fig4 #ai7 is found most abundantly1 and in a large proportion of cases to the exclusion of every other form1 in the lower shales4 ,it consisted of a large dome-shaped mass1 often three or four feet in diameter1 with trailing branches1 or roots1 spreading off horizontally to a distance of twenty feet4 ,in a few instances tree ferns have been found1 petrified in a horizontal position1 and being apparently a mere continuation of the stigmaria4 ,hence the stigmaria has been supposed to be the base of the tall tree ferns1 the leaves of which so abound in the upper shales4 ,if this is not the case1 there are no forms of the existing flora of the earth analogous to the stigmaria4 ,it is always found in connection with the coal-beds of the carboniferous formation1 and never with the coal-beds which sometimes occur in the later formations4 ,illustration3 ,fig4 #bj4 ,illustration3 ,fig4 #ba4 ,the tree ferns 7,fig4 #bj7 attained a height of fifty or sixty feet1 and a diameter of four feet4 ,they have received the name of ,sigillaria in consequence of the seal-like impressions 7,fig4 #ba7 with which the surface is covered1 and which are the scars left where the fronds have fallen off4 ,these fronds 7fern leaves7 are the most abundant fossil of the series4 ,they are distinguished by some peculiarity in form1 as the ,sphenopteris 7wedge-shaped fern leaf71 ,pachypteris 7thick fern leaf71 c4 7,figs4 #bb and #bc47 ,illustration3 ,fig4 #bb4 ,illustration3 ,fig4 #bc4 ,illustration3 ,fig4 #bd4 ,illustration3 ,fig4 #be4 ,there was another kind of ,sigillaria 7,fig4 #bd71 in which the surface was fluted1 and the markings are superficial1 and occur on the ridges4 ,it reached as great a size as the tree ferns1 but to what general class of plants it belonged is still doubtful4 ,the ,lepidodendron 7scale-covered tree7 7,fig4 #be7 is the fossil which most nearly resembled in general appearance our present forest trees4 ,specimens are found four feet in diameter and seventy feet in height4 ,in botanical characters it resembled1 in some respects1 the trailing club-mosses1 while in others it was very similar to the ,norfolk ,island pine4 ,illustration3 ,fig4 #bf4 ,the ,calamite 7,fig4 #bf7 was a plant resembling1 in its jointed and striated surface1 the equisetum 7rush71 but was sometimes twelve inches in diameter4 ,the carboniferous formation exists more or less abundantly in all the great divisions of the earth4 ,it occurs in nearly all of the countries of ,europe4 ,the largest deposits known are1 however1 in the ,united ,states2 especially in the ,states of ,pennsylvania and ,virginia1 and in ,ohio4 #d4 ,the ,new ,red ,sandstone4--,the lower division of this formation1 called the ,permian system1 consists of a thick mass of sandstones1 generally of a red color1 with occasional alternations of argillaceous rock1 succeeded by a series of magnesian limestones4 ,the upper division1 or ,triassic system1 is composed of a red conglomerate1 a limestone which has received the name of ,muschelkalk 7shelly limestone71 and a series of variegated marls and sandstones4 ,the ores of copper are found1 to considerable extent1 in this formation4 ,the rich copper mines of ,germany are in the magnesian limestone1 or1 as it is there called1 ,zechstein 7minestone74 ,the ,lake ,superior copper mines occur in a red sandstone formation1 which will probably be found to belong to this system4 ,the salt-beds1 salt springs1 and beds of gypsum1 are so1 generally found in this rock in ,england1 that it has been called by the ,english geologists the saliferous system4 ,it is1 however1 found that in other countries these minerals occur in equal abundance in formations of an earlier and later date4 ,illustration3 ,fig4 #bg4 ,the fossils of this system are not abundant4 ,in the ,permian portion1 impressions of fishes are found1 always with the peculiarity that the tail is heterocercal 7,fig4 #bg72 that is1 with the spine continued into the upper lobe4 ,the same peculiarity prevails in the carboniferous and all the earlier formations4 ,fishes with the tail homocercal begin to appear in the ,triassic portion of this system1 and are found in all the subsequent formations4 ,the remains of saurians also occur in this formation4 ,illustration3 ,fig4 #bh4 ,the red sandstones seem to have been better adapted to retain the forms which were impressed upon them than to preserve the organic remains which were deposited in them4 ,hence1 while they contain but few fossils1 the strata are often covered with ripple marks1 with sun cracks1 occasioned by contraction while drying1 or with depressions produced by rain-drops1 and the pits are sometimes so perfect as to show the direction of the wind when the drops fell4 7,fig4 #bh47 ,the tracks of animals are also well preserved4 ,some of them were produced by reptiles 7,fig4 #bi1 c71 and some probably by marsupial animals1 but most of them by birds 7a1 b74 ,president ,hitchcock has distinguished the tracks of more than thirty species in the sandstones of the ,connecticut valley4 ,birds1 reptiles and marsupial animals1 seem to have been first introduced during this period4 ,illustration3 ,fig4 #bi4 ,the new red sandstone is well developed in all its members on the continent of ,europe4 ,in ,england1 all the members are present1 except the ,muschelkalk4 ,the ,triassic portion of it occurs in ,north ,america4 ,it is found in detached portions1 probably as parts of a continuous formation1 in ,nova ,scotia1 the eastern part of ,maine1 the ,connecticut valley1 and from ,new ,jersey southward through ,pennsylvania1 ,maryland1 c41 to ,south ,carolina4 #e4 ,the ,olitic ,system4--,the lower portion of this system is the ,lias1 and consists of a series of fissile1 argillaceous limestone1 marl1 and clays4 ,the ,olite forms the intermediate member of the system1 and consists of alternations of clay1 arenaceous rock and limestone4 ,some of the limestones have an olitic structure1 and the whole system takes its name from this circumstance1 though this structure is not found in all parts of it1 and is often found in other formations4 ,the central part of the olite1 the coral rag1 is principally a mass of corals and comminuted shells4 ,the ,wealden1 the highest member of the olitic system1 is an estuary deposit1 consisting of calcareous beds1 followed by sandstone1 and terminated by the ,wealden clay4 ,this system is throughout highly calcareous1 and furnishes1 wherever it is developed1 valuable materials for architectural and ornamental purposes4 ,this system is distinguished for the great amount and variety of its organic remains4 ,the vegetable productions were intermediate between those of the coal period and those of the present time4 ,the upper olite1 in the south of ,england1 contains the stumps of trees and other plants1 rooted in a black carbonaceous layer1 evidently the soil from which they grew4 ,these stumps and prostrate trunks are the remains of coniferous trees of large growth4 7,fig4 #cj47 ,corals occur in great abundance2 also encrinites 7,fig4 #ca71 mollusks 7,fig4 #cb71 and cephalopoda4 ,illustration3 ,fig4 #cj4 ,illustration3 ,fig4 #ca4 ,illustration3 ,fig4 #cb4 ,but this system is specially characterized by the remains of saurian reptiles4 ,the ,ichthyosaurus 7,fig4 #cc1 a7 was a marine animal1 having the general form of a fish1 while its head1 and especially its teeth1 resemble those of the crocodile4 ,it was an air-breathing animal like the cetacea1 and was furnished with similar paddles4 ,it was carnivorous1 and was undoubtedly the largest and most formidable animal existing in the earlier part of the olitic period4 ,its length could not have been less than thirty or forty feet4 ,illustration3 ,fig4 #cc4 ,the ,plesiosaurus 7,fig4 #cc1 b7 was also a marine animal1 and in ninny respects similar to the ,ichthyosaurus2 but its general form was more slender1 its head was small1 and its neck was of great length1 the cervical vertebr exceeding in number those of the swan4 ,illustration3 ,fig4 #cd4 ,the ,pterodactyle 7,fig4 #cd7 was a small saurian1 of the size1 probably1 of our largest eagle4 ,the finger-bones1 which in the other saurians form the paddles1 are in the ,pterodactyle very much lengthened1 so as to support a membranous expansion1 like that of the bat4 ,these wings were of sufficient size to enable it to sustain itself in the air1 and to make a rapid and easy flight4 ,the ,iguanodon is a ,wealden fossil1 remarkable for its great magnitude4 ,it is estimated that its length was seventy feet4 ,it was a lizard1 adapted for motion on land1 and was herbivorous4 ,this formation is well developed in ,england1 and1 with the exception of the ,wealden1 on the continent of ,europe4 ,it has been supposed that no part of the olitic series was to be found in this country2 but there is a highly arenaceous rock occupying the valley of the ,james river1 in the vicinity of ,richmond1 ,virginia1 of considerable extent1 and a thousand feet in thickness1 containing a bed of coal of forty feet in thickness1 which1 from its fossils1 must be referred to the olitic series4 #f4 ,the ,cretaceous ,formation4--,the lower part of this formation consists of greensand1 interstratified with beds of clay4 ,the intermediate portion is a mixture of argillaceous greensand and impure chalk4 ,the upper part is composed of chalk1 which is a friable1 nearly pure carbonate of lime4 ,the strata of chalk are separated1 at intervals of from three to six feet1 by layers of flint1 either in the form of nodules or of continuous strata4 ,these characters1 by which the cretaceous system is known in ,england1 are but partially recognized elsewhere4 ,thus1 in the ,alps1 the ,neocomian ,system1 consisting of crystalline limestones1 is the equivalent of the ,english greensand2 while the greensand of this country is the equivalent of the white chalk of ,england4 ,illustration3 ,fig4 #ce4 ,illustration3 ,fig4 #cf4 ,the fossils of the cretaceous formation are very different from those of the olite1 and are such as to show that it was deposited in deep seas4 ,microscopic shells are often so abundant as to constitute a large proportion of the mass4 ,zophytes are very numerous1 such as sponges1 corals1 star-fishes 7,fig4 #ce1 d e71 and a few crinoidea 7b74 ,mollusks were also abundant1 and cephalopoda1 consisting of chamber-shells and belemnites 7,fig4 #cf74 ,the belemnite probably resembled the existing cuttle-fish2 but the remains consist1 in most cases1 of a partially hollow calcareous substance 7b71 which was contained within the animal1 and formed its skeleton4 ,the chalk and greensand are largely developed in ,england2 and the same formation1 with different lithological characters1 is found in great force flanking the principal mountain ranges of southern ,europe1 and extending into ,asia4 ,in this country the system commences with the greensand and friable limestones of ,new ,jersey1 and following the ,alleghany range to its southern termination1 it bends around into a north-western direction1 and is continued into ,missouri4 #g4 ,the ,tertiary ,system4--,the tertiary strata embrace the formations from the cretaceous to the human era4 ,they consist of clay1 sand1 sandstone1 marl and limestone1 and are distinguished from the lower rocks by being less consolidated2 though the limestones are in some instances solidified1 and resemble the strata of earlier origin4 ,the tertiary strata are generally of less thickness than the older formations1 and less continuous1 being local deposits formed in lakes and estuaries4 ,in a few instances they have been thrown into inclined positions1 though in most cases they have been but slightly disturbed1 and raised but a few hundred feet above the present level of the sea4 ,the late tertiary strata seldom overlap the older1 so as to indicate their relative ages by superposition4 ,they have therefore been separated into groups according to the proportions of living and extinct species of shells which they are found to contain4 ,the oldest tertiary or ,eocene formation,a contains only four per cent1 of living species1 the ,miocene contains seventeen per cent41 the ,pleiocene forty per cent41 and the ,pleistocene ninety per cent4 ,a ,es1 dawn1 and kainos1 recent4 ,the formation which commenced at the dawn of the recent period1 containing but a small number of living species4 ,miocene 7meion1 less71 less recent than the ,pleiocene 7pleion1 more74 ,pleistocene 7pleistos1 most71 most recent4 ,during the pleistocene period1 peculiar conditions existed1 by which a great amount of loose material1 known by the name of drift1 was spread over the northern portions of both hemispheres4 ,in ,america it is found from ,nova ,scotia nearly to the ,rocky ,mountains1 and extending as far south as ,pennsylvania and the ,ohio river4 ,in ,europe1 it is found from the ,atlantic to the ,ural ,mountains1 and reaching south into ,germany and ,poland4 ,it is also found in the colder portions of ,south ,america1 and in the vicinity of several mountains1 as the ,alps4 ,it consists of irregular accumulations of earthy substances of different degrees of fineness1 but characterized by containing masses of rock of considerable size1 often of many tons weight1 called boulders4 ,rocks having the same lithological characters exist in situ north of where the boulders and other drift are now found1 though at a distance often of one or two hundred miles4 ,there can be no doubt but that the drift has been transported from these northern localities2 and the polished1 striated and grooved condition of the rocky surface1 wherever the drift is distributed1 has obviously been produced by the passage of the drift materials over it4 ,towards the close of this period1 while the land was a few hundred feet below its present level1 there were deposited in the valleys of the drift region beds of blue and gray clay1 materials which are used in making bricks and coarse pottery2 also beds of sand1 sometimes evenly spread out1 but often thrown into irregular mounds and ridges4 ,in regions which are not covered with drift1--as the south of ,europe and the ,united ,states1--the pleistocene deposits are succeeded1 without apparent change of conditions1 by those which are now taking place4 ,the formations of the tertiary period are distinguished from those of the cretaceous period by the absence of deep-sea fossils1 and from the olite by the absence of its characteristic saurians4 ,the mollusks are also very different1 such genera as the cerethium 7,fig4 #cg71 murex 7,fig4 #ch71 and conus 7,fig4 #ci71 which abound in the present seas1 first appearing in the tertiary period4 ,the nummulite 7,fig4 #dj71 a peculiar form of chambered shell1 is so abundant as to constitute in some places almost the entire rock4 ,the period is however characterized by the existence of a large number of pachydermatous animals1 of which the tapir1 hog1 horse and elephant1 are examples of living species4 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #ch4 ,illustration3 ,fig4 #ci4 ,illustration3 ,fig4 #dj4 ,the ,paleotherium 7,fig4 #da7 resembled1 in most respects1 the tapir4 ,it was furnished with a short proboscis1 and the foot was divided into three toes4 ,the length of the largest species was about that of the horse2 but its body was larger1 and it was of less height4 ,illustration3 ,fig4 #da4 ,illustration3 ,fig4 #db4 ,the ,anoplotherium 7,fig4 #db7 was a more slender animal1 and resembled in size and general form the gazelle4 ,the ,megatherium1 an animal of the late tertiary epoch1 was larger than the existing species of elephant1 and in its general structure and habits resembled the sloth4 ,the ,mastodon 7,fig4 #dc7 lived during the latest portion of the tertiary epoch4 ,its remains are found most abundantly where the animal seems to have perished by sinking into the soft marshy ground near the brackish springs of ,new ,york and ,kentucky4 ,but they are found also in ,europe and ,asia4 ,it was larger than any existing land animal1 and was nearly allied in structure and habits to the elephant4 ,illustration3 ,fig4 #dc4 ,the ,mammoth was a species of elephant1 now extinct1 of which remains are found with those of the mastodon1 but in the greatest abundance in ,europe and ,asia4 ,a large number of skeletons1 many of them imperfect1 have been discovered in the low grounds in the south-east of ,england4 ,it was this animal which was found encased in ice and sand in ,siberia1 in #ahjd4 ,contemporaneously with the existence of these huge animals1 a near approach was made to the present fauna of the earth1 by the introduction of ruminant animals resembling the ox and deer1 and especially by the existence of the class of animals which in anatomical characters stands next to man1 the apes and monkeys4 ,the tertiary system1 though not generally so continuous over extended areas as the older formations1 yet constitutes the surface of a very large part of ,europe4 7,see ,fig4 #ei47 ,in the ,united ,states the earlier portion is found along the seaboard1 from ,new ,jersey to ,louisiana1 and extending back towards the mountains to a distance varying from ten to one hundred miles4 ,the later deposits are found in detached portions throughout the ,eastern and ,middle ,states4 ,it covers a large surface in ,south ,america1 and is found in ,india4 #h4 ,the ,recent ,formation4--,it is intended to embrace in this term strata which have been formed since the creation of man4 ,it is1 however1 impossible to separate them by any well-defined characters from those of the tertiary period4 ,the recent formation consists of land which is forming by the filling up of lakes1 and by the increase of deltas from the accumulated sediment which rivers have furnished4 ,there is1 however1 no doubt but that formations on a large scale have continued in progress over extensive areas of the bed of the sea2 and they have been no less rapid1 we may presume1 than they were in earlier periods4 ,but1 though they are preserving the records of the present era1 they will probably remain in a great measure inaccessible for many ages4 ,these deposits1 so far as they are accessible1 are found to contain the remains of plants and animals 7including man7 now living in the vicinity where the deposits are forming4 ,,section ,,vi4--,,fossils4 ,any organic substance imbedded in a geological formation1 or any product of organic life1 as a coprolite or a coin1 or any marking which an organic substance has given to a rock1 is regarded as a fossil4 ,the study of fossils1 as a branch of practical geology1 requires an acquaintance with the principles and the minute details of botany and zoology4 ,without this knowledge1 however1 many of the general conclusions to which the study of fossils has led may be understood4 #a4 ,fossils are preserved in different ways4--,when any organic substance is imbedded in a forming rock1 it may itself remain2 or it may be removed by the infiltration of water1 or other causes1 so gradually as to leave its form1 and even its most delicate markings1 in the rock2 or some mineral substance may have been substituted1 and fill the space which the organic substance once occupied2 that is1 it may be an organic substance preserved1 it may be an impression of it1 or it may be a cast of it4 #b4 ,the process by which the substitution in this last case is effected is called mineralization4 ,the mineralizing ingredient is generally derived from the contiguous rock4 ,in siliceous rocks it is silex4 ,in calcareous rocks it is carbonate of lime4 ,when iron is diffused through a rock1 it often becomes the mineralizer4 ,the substituted mineral is generally a very perfect representation of the original fossil4 ,we cannot therefore suppose that the original substance was entirely removed before any of the mineral matter was deposited4 ,the substitution must have taken place particle by particle1 as the organic matter was removed4 ,fossils are1 in fact1 often found1 in which the mineralization has been arrested after it had commenced1 so that the fossil is in part an organic and in part a mineral substance4 ,it has been proved1 by direct experiment1 that these changes of removal and substitution are simultaneous4 ,pieces of wood were placed in a solution of sulphate of iron4 ,after a few days1 the wood was found to be partially mineralized1 and after the remaining ligneous matter had been removed by exposing it to a red heat1 oxide of iron was found to have taken the form of the wood so exactly1 that even the dotted vessels1 peculiar to the species employed1 were distinctly visible under the microscope4 #c4 ,as the fossiliferous strata are generally of marine origin1 it is to be presumed that only a small proportion of terrestrial animals are preserved2 and our knowledge of the organic remains which are preserved is yet so imperfect1 that discoveries are constantly making1 as examinations are extended4 ,still1 enough is known to enable us to draw some satisfactory conclusions as to the order in which living beings were created upon the earth4 ,though most of the earlier organic forms which have been preserved are of animal origin1 yet vegetable remains occasionally occur in connection with them1 and we must suppose vegetables to have been produced abundantly4 ,for all animal food consists of vegetable substances1 or of animal substances which have once existed in the vegetable form4 ,no animal is capable of effecting those combinations of inorganic matter upon which its growth and sustenance depend4 ,we may therefore conclude that the introduction of animals and vegetables was contemporaneous4 ,the greatest development of vegetable life was1 however1 during the carboniferous period4 ,the design of this abundant growth was prospective4 ,it was not produced for the support of animal life1 but for fuel1 and stored till man should be introduced1 and so far advanced in civilization as to make this supply of carbonaceous matter subservient to his wants and happiness4 ,in the earlier periods1 the lower forms of animal life were1 beyond all comparison1 the most abundant2 yet the four great divisions of the animal kingdom1 ,radiated1 ,articulated1 ,molluscous1 and ,vertebrated animals1 were all represented4 ,there is1 however1 no evidence that any vertebrated animals1 except fishes1 were created till after the carboniferous period4 ,in the next formation1 the new red sandstone1 we find the tracks of reptiles and birds1 and probably of marsupial animals4 ,the first evidence of the existence of mammalia in great numbers is in the tertiary period1 when the pachydermata and edentata were so much more abundant than they have ever been since1 and when the bimana first appear4 ,but there is no evidence from geology that man existed till after the close of the tertiary period4 ,the grounds upon which contrary statements have sometimes been made are untenable4 ,in ,ohio a very perfect impression of a human foot was found on a slab of limestone of the silurian age4 ,but it was subsequently ascertained to have been common for the aborigines1 in the vicinity of their encampments1 to cut in the rocks1 with surprising accuracy1 the forms of the tracks of man and other animals4 ,there is a human skeleton in the ,british ,museum imbedded in solid limestone1 and another in ,paris1 both taken from ,guadaloupe4 ,it was at one time supposed1 from the degree of solidification of the limestone1 that it must have been formed at an early geological period2 but it is found that the beach-sand of that island now solidifies rapidly1 from the carbonate of lime which the waters there hold in solution4 ,it is rendered probable that the skeletons found there have not been buried more than a century and a half4 #d4 ,as many parts of the bed of the present seas1 which are probably receiving detrital matter constantly1 are unfavorable for the development of animal life1 while other parts are highly favorable1 it might be presumed that animal life would be equally scanty in particular localities while the earlier rocks were forming1 and in other localities very abundant4 ,hence some strata1 for hundreds of feet in thickness1 are composed almost entirely of fossils1 while other strata are nearly or quite destitute of them4 ,the same member of a formation may in one place be full of fossils1 and in another without them4 ,the distribution of fossils is therefore subject to no general law2 at least1 none of which we can avail ourselves1 in the search for them4 #e4 ,the value of fossils in geology consists in the use which is made of them in determining the origin and age of strata4 ,as the animal species which inhabit bodies of fresh water are always different from those found in the sea1 their remains constitute the best means of determining whether a formation is of fresh water or marine origin4 ,in order to decide this point1 it may1 in some cases1 be necessary to be acquainted with the habits of particular species4 ,in most cases1 however1 it will be sufficient to remember that in fresh-water formations1 first1 there are no sponges1 corals1 or chambered shells2 second1 the univalves all have entire mouths 7,fig4 #dd74 ,third1 the bivalves are all bimuscular 7,fig4 #dg74 ,if1 therefore1 a formation is found to contain sponge1 coral1 a chambered shell1 a univalve with a deeply notched mouth 7,fig4 #de71 or a unimuscular bivalve 7,fig4 #df71 it must be considered a marine formation4 ,illustration3 ,fig4 #dd4 ,illustration3 ,fig4 #de4 ,illustration3 ,fig4 #df4 ,illustration3 ,fig4 #dg4 ,we have seen that the same formation1 as exhibited in different places1 differs in its thickness1 composition and degree of solidification4 ,if we could trace the strata through all the intermediate space1 we might be certain of their being the same formation1 notwithstanding the change in lithological characters4 ,but this can seldom be done1 even for a few miles in extent4 ,sections of the strata are obtained only occasionally1 where rivers have cut through them1 or where1 over limited areas1 the soil has been removed from the outcropping edges4 ,it is also frequently the case that the strata are so much disturbed that their position will furnish no aid in determining their age4 ,when folded axes occur 7as here represented71 the older strata are often the uppermost4 ,there is an instance in the ,alps in which strata of vast thickness have been inverted during the process of upheaval1 and now rest on a bed of rock formed from the debris which they had supplied4 ,illustration ,and yet it is important to determine what formations are of the same age1 notwithstanding their displacements1 difference in lithological characters1 and separation by great distances and by mountains or oceans4 ,this determination can be made only by a comparison of the imbedded fossils4 ,it is found that every formation1 and every important member of a formation1 contains an assemblage of fossils peculiar to itself4 ,when very widely separated1 the species of fossils may not be identical1 but so very similar that they are regarded as equivalent species4 ,the identification of formations consists in the identification of fossils4 ,it is for this purpose mainly that fossils are regarded as of so great importance4 #f4 ,if each formation is characterized by the presence of new species1 it follows that the work of creation was a progressive one1 continued through long periods of time4 ,the latest creation of which we have any geological evidence is that of man4 ,and if the leading design of the existence of this earth was as a theatre for the development of moral character1 it is to be presumed that the work of creation ceased when a species possessing moral capacities had been introduced4 ,it follows also1 from what has been said1 that there has been a constant disappearance1 a death1 of species4 ,it would seem that each species has a life assigned to it1 which is to be completed and surrendered4 ,though its continuance is many times longer than the life of any individual of the species1 yet it is the course of nature that species should disappear4 ,there may be something in the constitution of each species by which its continuance is limited1 making an old age and death necessary1 as it is in individuals4 ,but there are other causes by which the duration of species may often be terminated4 ,the subsidence of ,new ,holland would cause the destruction of a large number of species4 ,the preservation of the human species was at one time effected only by a special and miraculous interference4 ,slowly operating causes are now at work1 by which many species1 such as the elephant1 wolf and tiger1 will at length become extinct4 ,their existence in a natural state cannot long be continued in a civilized country4 ,the forest1 their natural abode1 disappears1 and some are intentionally destroyed1 because they render life and property unsafe4 ,under the operation of these causes1 the ,irish elk 7cervus giganteus7 has become extinct1 probably within the human era4 ,the ,dodo1 a gallinaceous bird1 found living when maritime communication between ,europe and the ,east ,indies was first established1 is now extinct4 ,the ,apteryx1 a bird belonging to ,new ,zealand1 has probably become extinct since the commencement of the present century4 ,,section ,,vii4--,,the ,,time ,,necessary ,,for ,,the ,,formation ,,of ,,the ,,stratified ,,rocks4 ,there are no means of which the geologist can avail himself to determine the antiquity of the earth1 or the amount of time since the sedimentary deposits commenced4 ,but a nigh degree of antiquity may yet be shown4 ,the materials for all the stratified rocks have been obtained by the destruction of previously solidified igneous rocks4 ,this destruction may have been accomplished in part by the operation of volcanic forces1 but much of it is the result of slow disintegration1 and of the eroding power of running water2 and we can scarcely conceive of a period sufficiently protracted for such results4 ,this conclusion of the high antiquity of the earth is confirmed by observing that the stratified rocks consist of layers often not thicker than sheets of paper1 and probably not averaging the tenth of an inch2 and yet each layer is separate from the rest1 in consequence of some change in the conditions under which it was deposited4 ,each layer was probably produced by the deposition of all the sediment furnished at one time1 and hence only as many layers would be formed in a year as the number of freshets in the rivers which furnished the materials4 ,if we consider the fossiliferous and metamorphic rocks to be each forty thousand feet in thickness1--which is not too large an estimate1--we must reckon the years by hundreds of thousands to make the time sufficiently extended for the result4 ,all the formations of any considerable extent now above the surface of the sea existed before the creation of man1 for none of them contain any evidence of the existence of human beings2 and if they had existed while these strata were forming1 sufficient evidence would have been left of the fact1 either in the form of fossilized human bones1 or of works of human art4 ,hence1 whatever be the estimate which we form of the antiquity of the earth1 from the slowness of denudation1 or from the thickness of the strata1 we must now add to that estimate the period elapsed since the creation of the human species4 ,we have seen that at different periods of the earth's history different species of animals inhabited it4 ,we are unable to fix with accuracy the ordinary duration of species4 ,but the species which are now extinct probably had an existence as long-continued as will be enjoyed by species now living4 ,many recent species are known to have existed at least nearly six thousand years1 without1 in most cases1 any indications of their soon becoming extinct4 ,whatever period be assigned as the ordinary duration of species1 that period has been several times repeated2 for the earth has been several times re-peopled1 and every time by species which had not before existed4 ,moreover1 the amount of organic matter in the strata must have required long periods of time for its accumulation4 ,the vegetable deposits1 now converted into coal1 are generally several feet thick1 and often over a hundred feet1 and are known to extend over several thousand square miles1 both in this country and in ,europe4 ,many of the sedimentary rocks consist almost entirely of animal remains4 ,the mountain limestone1 for instance1 is eight hundred feet or more in thickness1 and in some places consists of the exuvi of encrinites and testacea4 ,in other cases the length of time required is shown1 not from the amount of organic remains1 but from the evidence that they were deposited very slowly4 ,the polishing stone called tripoli is found in beds of ten or twelve feet in thickness1 and is composed entirely of the siliceous shells of animalcules1 so minute that1 according to the estimate of ,ehrenberg1 the number in a cubic inch is forty-one billions4 ,several other rocks1 such as semi-opal and flint1 are sometimes found to have a similar constitution4 ,the time necessary for the accumulation of beds several feet thick by the shells of animalcules so minute must have been very great4 ,each of these facts carries us back to a period immeasurably anterior to the creation of man1 as the epoch when the sedimentary deposits commenced4 ,there are no facts in geology which point to a different conclusion4 ,it is of the utmost importance to the geological student to familiarize himself with this principle4 ,it will assist him in comprehending the greatness of geological changes1 and in applying other principles in explanation of geological phenomena4 ,this principle1 so obvious to any one who allows himself to reason from the facts which geology presents1 has sometimes been regarded as at variance with the ,mosaic account of the creation4 ,and if this account really assigns an antiquity to the earth of not more than six thousand years1 the difficulty exists4 ,the statements made by ,moses are found1 upon examination1 to be of the most general character4 ,they assert1 in the first place1 simply that ,in the beginning ,god created the heaven and the earth4 ,the time which elapsed after this first act1 and previously to the acts of creation subsequently recorded1 is not limited by the sacred narrative4 ,it may have been during this indefinite lapse of time that ,god gave existence and enjoyment to a large number of animal species on the surface of the earth1 and at the same time effected most of those physical changes in the crust of it which have rendered it a fit abode for intellectual and moral beings4 ,but if the word day1 in the first chapter of ,genesis1 be considered to mean a prolonged period 7and philologists regard such an interpretation as admissible71 then that chapter is a record of the most important events in the history of the earth up to and including the introduction of man4 ,and the account1 thus understood1 coincides with the results of geological examinations4 ,instead1 then1 of discrepancy between the works and the word of ,god1 we have this remarkable fact1 that a history of the earth1 written long before the science of geology was known1 is not contradicted1 but confirmed1 by the progress of science thus far4 ,,chapter ,,iii4 ,,of ,,the ,,changes ,,to ,,which ,,the ,,crust ,,of ,,the ,,earth ,,has ,,been ,,subjected4 ,,section ,i4--,,changes ,,which ,,have ,,taken ,,place ,,at ,,great ,,depths ,,below ,,the ,,surface4 ,the lowest change of winch we can gain any information is the formation of granite4 ,it will be shown hereafter that it has been in a melted state1 and that it has taken its present form on cooling4 ,but whether any considerable portions of the granitic masses1 or of the melted masses now below the surface1 have resulted from the fusion of stratified rocks1 we have not the means of determining4 ,it is1 however1 not improbable1 that in the changes of level to which the crust of the earth has been subjected1 the stratified rocks may have gone down so far as to become melted4 ,at the same time1 the melted rock which is thrown to the surface by volcanoes is subjected to the various destroying agencies by which it becomes sedimentary matter1 to be deposited as mechanical strata4 ,thus1 as the igneous rocks from below are brought up to furnish materials for mechanical strata1 there must be an equal amount of depression of the mechanical strata towards the seats of igneous action4 ,and if this change takes place more rapidly than the thickness of crust increases1 then portions of the sedimentary rocks must be undergoing fusion4 ,next above the granite an immense thickness of rock occurs1 which exhibits1 from its stratification and from the water-worn fragments which it contains1 distinct evidence of its mechanical origin4 ,and yet it is very different from the later mechanical formations4 ,it is more highly crystalline2 it has1 to a great extent1 assumed a cleavage distinct from the planes of stratification1 and chemical affinity has been so far active as to produce new combinations1 and give to them their peculiar crystalline form1 as in the case of garnets1 iron pyrites1 c4 ,these strata also differ from those above them in containing no organic remains4 ,it is not certain that organic life existed on the earth at the time when these rocks were deposited4 ,either it did not1 or the evidence of it in the strata of that period has been obliterated4 ,the changes have at least been sufficient to justify their being characterized as metamorphic rocks4 ,,section ,,ii4--,,changes ,,in ,,the ,,mass ,,of ,,the ,,stratified ,,rocks4 #a4 ,the stratified rocks were deposited as mud or sand1 and were at first in a yielding state4 ,most of these deposits have become solidified rock1 such as limestone1 clay slate and sandstone4 ,the chalk of ,england is1 however1 but imperfectly consolidated1 the great sandstone formation of ,new ,holland is a friable mass easily disintegrated1 and occasionally beds of clay in a plastic state are found as far down as the coal4 ,among the later rocks the solidification is less general1 though there is some degree of hardening in all except the most superficial layers4 ,the fissile structure results from the solidification of the particles composing each layer separately4 #b4 ,since the solidification of the strata1 or perhaps in connection with it1 there has been something of movement among the particles1 resulting in mineral veins1 conchoidal structure1 c4 ,one of the most general changes of this kind is that by which a mass becomes separable into thin sheets1 independent of the stratification1 and not parallel with it4 ,this structure is represented by ,fig4 #dh1 in which the heavier lines are those of stratification1 and the lighter of cleavage4 #c4 ,the strata have been everywhere more or less broken1 and the fractures1 nearly vertical1 extend to groat depths4 ,when a fracture reaches the surface1 it often becomes a channel for water4 ,it is thus widened by the erosion1 the deepest parts become filled with debris1 and it becomes a gorge1 ravine or valley4 ,illustration3 ,fig4 #dh4 ,if the fracture does not come to the surface1 it becomes a cavern4 ,in limestone1 caverns which are formed in this way are very frequent1 and extend for many miles4 ,there is generally a stream of water running through them1 but not of sufficient volume to have produced the erosion which has been effected4 ,when the sides of the fracture are but little separated1 some mineral often separates itself from the adjacent rock1 and filling up the space1 reunites the broken parts4 ,it is then called a vein of segregation 7,fig4 #di1 a b74 ,but the fracture is more frequently filled with some volcanic rock injected from below4 ,it is then a dike 7c d71 and may have a width of many rods1 though it often diminishes in width till it is a mere thread4 ,a dike of which the injected material is a metallic ore is a mineral vein4 ,illustration3 ,fig4 #di4 #d4 ,the uplifting force by which the fracture is produced has frequently raised the rock on one side higher than it has on the other4 ,this is called a fault4 7,fig4 #ej47 ,the unequal movements by which the fault is produced seem in some instances to have been repeated several times1 and the grinding of the broken edges upon each other has polished and striated the sides of the fracture4 ,illustration3 ,fig4 #ej4 ,illustration3 ,fig4 #ea4 ,illustration3 ,fig4 #eb4 #e4 ,sedimentary rocks are often found with the planes of their strata more or less inclined4 ,it is evident that they were not thus formed4 ,the depositions of sediment from water will always be horizontal1 or1 at most1 only slightly inclined4 ,but there is often evidence in the rock itself that its strata were once horizontal4 ,it is frequently observed that vertical strata contain pebbles with their longer axes in the plane of the strata4 7,fig4 #ea47 ,when these pebbles were deposited1 the longer axes would take1 on an obvious mechanical principle1 a horizontal position4 ,their present vertical position must have resulted from a change in the position of the strata in which they are enclosed4 ,the same thing is shown by the position of a petrified forest in the south of ,england1 known as the ,portland dirt-bed4 ,some parts of it are inclined at an angle of forty-five degrees4 ,the position of the vegetable remains 7,fig4 #eb7 shows that when they were growing the surface was horizontal4 ,the line b d 7,fig4 #ec71 on inclined strata which makes with the horizon the greatest angle1 is called the direction of the dip4 ,the angle thus formed 7a b d7 is the angle of inclination4 ,when inclined strata come to the surface1 the exposed edge1 b c1 is the outcrop1 and the line of outcrop on a horizontal surface is called the strike of the strata4 ,illustration3 ,fig4 #ec4 ,when the inclined position is produced by an uplift of the strata1 along a given line1 so that they dip in opposite directions1 this line is called an anticlinal axis1 as at ,fig4 #ed4 ,if1 however1 the strata are fractured along this line1 as at b1 the fracture becomes a valley of elevation4 ,illustration3 ,fig4 #ed4 ,if depression take place along a given line1 as at c1 the strata will dip towards this line1 and it will be a synclinal axis4 ,the depression will be a valley of subsidence4 ,a synclinal axis would also be produced by an elevation of the strata1 as at d and e1 on each side of it1 and the valley thus produced is one of elevation4 ,when successive sets of strata1 as f and d1 ,fig4 #ec1 are not parallel1 they are said to be unconformable4 ,illustration3 ,fig4 #ee4 ,illustration3 ,fig4 #ef4 #f4 ,when the strata are subjected to displacement1 they do not always take a merely inclined position1 but are often contorted 7,fig4 #ee71 or folded together 7,fig4 #ef74 ,these folded axes frequently succeed each other for many miles4 7,see ,figs4 #g and #hb47 ,in the case represented by ,fig4 #ef1 if the highest portion has been removed1 so that the line a b represents the actual surface1 we shall have apparently a succession of deposits1 of which those at b would be the newest1 and the oldest would be found at a1 when in fact the strata at the extremities are parts of the same layer4 ,it is probable that disturbances like those now mentioned have been taking place continually1 in different places1 from the earliest times4 ,there have been no periods of universal disturbance1 and none of universal repose4 ,on the contrary1 the periods of disturbance in one part of the world have been periods of repose in another4 ,for example1 the coal measures of ,europe were much broken and disturbed before the deposition of the new red sandstone1 and the close of the coal period was at one time supposed to have been a period of general convulsion4 ,it is now ascertained that the principal coal-fields in this country were not much disturbed at that period1 and have not been since4 ,,section ,,iii4--,,changes ,,of ,,elevation ,,and ,,subsidence4 ,the continents1 if we except the more rugged and broken portions1 rise from the sea with an almost imperceptible ascent2 and even the mountains have a much gentler slope than we are apt to suppose1 so that a section of the earth parallel to the equator would be almost a perfect circle4 ,the slope of a mountain1 from its base to its highest point1 rarely forms with the horizon an angle of as much as twelve degrees4 ,in the following figure 7#eg71 ,a represents the peak of ,chimborazo1 ,b of ,teneriffe1 ,c of tna1 and ,d of ,mount ,loa1 the principal volcano of the ,sandwich ,islands4 ,the highest mountains would be represented on a twelve-inch globe by an altitude of less than the one-hundredth of an inch above the level of the sea4 ,but the rising and sinking of these masses1 though so small compared with the dimensions of the earth1 are yet geological changes on the largest scale4 #a4 ,the ,elevation of ,mountains4--,mountains have formerly been covered with the waters of the ocean4 ,this is evident1 in the case of some mountains1 from the existence of stratified rocks reaching to the summits4 ,the stratification could have been produced only by deposition from water4 ,it is1 moreover1 evident from the existence of marine fossils1 distributed through these strata1 so abundantly1 that they cannot be accounted for on any other hypothesis than that the animals lived and died where the remains of them are now found4 ,these strata must therefore have formed the bed of the sea while the fossils were accumulating4 ,illustration3 ,fig4 #eg4 ,there is no direct evidence that the granitic mountain peaks were ever submerged4 ,but there is reason for believing that the sedimentary strata which now occupy the lower slopes were1 at the time of their deposition1 continuous1--the igneous rock having subsequently broken through them1--so that the waters of the ocean once rested on the whole area which the mountain now occupies6 ,if the ocean could ever have been above its present level sufficiently to have covered all the sedimentary rocks1 we might assume that the height of mountains has not been changed4 ,but the level of the ocean cannot be subject to much variation4 ,the total amount of water on the globe is always the same4 ,if the continents and mountains were all submerged at once1 and the waters were expanded by the highest temperature consistent with the liquid form1 there would not be a change of level of more than two hundred and fifty feet4 ,we may assume1 then1 that the ocean level has always been essentially the same that it now is4 ,we must therefore conclude that the sedimentary rocks1 and the mountains of which they form a part1 have been elevated to their present position from the bed of the sea4 ,different mountain ranges have been elevated at different periods4 ,the silurian and carboniferous formations were deposited before the ,alleghany ,mountains1 which they contributed to form1 were elevated2 while the new red sandstone and the cretaceous and tertiary formations were deposited subsequently to the upheaval4 ,they are accordingly found at the base of the range1 nearly horizontal1 and have risen above the level of the ocean only as the continent generally has risen4 ,the ,pyrenees were elevated after the deposition of the cretaceous rocks1 and have carried them up so that they appear at a high angle1 while the tertiary rocks at the base are horizontal1 as in the ,united ,states4 ,the ,andes have carried up the tertiary rocks with them1 and their elevation must therefore belong to a recent period4 ,it appears that they are even yet rising4 ,it has recently been shown that the ,alps have been subjected to upheaval at several distinct periods4 ,at the close of the silurian period they formed a cluster of islands4 ,at the commencement of the tertiary period they became a mountain range1 and at the close of that period they were thrown up some two thousand feet higher1 to their present position4 ,nearly the same things will probably be found true of other mountain ranges1 when their structure has been minutely studied4 ,the elevation of contiguous parallel ridges will necessarily leave intervening valleys of elevation4 ,as mountain ranges generally consist of several such ridges1 valleys of this description are numerous1 and they are often of great extent4 ,it is obvious that there are mountains in the sea of as great height above the lowest valleys as the mountains of continents are above the level of the sea4 ,if a new continent should hereafter be formed by the elevation of a large area of the bed of the sea1 the existing mountains1 now appearing in the form of islands1 would partake of the general movement1 and the new continent would have the same general diversities of surface as existing continents4 ,the mountains would have existed long before the continent4 ,it is therefore to be supposed that the mountains of the present continents were elevated before the continents1 and that they stood for long periods as islands1 exposed to the action of waves1 tides1 and marine currents4 #b4 ,the ,elevation of ,continents4--,continents have been elevated by so slow a movement that it has not generally been perceived1 even when they have been peopled by nations advanced in civilization4 ,and yet satisfactory evidence is always left of former sea-levels4 ,almost every seaboard furnishes examples of beaches1 evidently once washed by the sea1 but now elevated more or less above high water4 ,at ,lubec1 near the northern extremity of the coast of ,maine1 barnacles,b are found attached to the rocks eighteen feet above high water4 ,the pilots at that place1 and for a hundred miles north and south of it1 speak of the ship-channels as diminishing in depth1 though it is certain that they are not filling up4 ,such facts are to be explained only by supposing that the coast is rising4 ,b ,the barnacle is a marine animal1 permanently fixed to the rocks1 and live but a short time without being surrounded by sea-water4 ,lakes are numerous throughout the northern portions of ,north ,america1 which are receiving annually large quantities of sediment1 and must ultimately become alluvial plains4 ,those of moderate depth1 as ,lake ,erie1 cannot require periods very protracted to fill them4 ,their continuance in such abundance indicates that the elevation of the continent to its present height is comparatively recent4 ,this conclusion is confirmed by evidence of another kind4 ,throughout this region of lakes1 beds of clay containing the remains of existing species of marine animals1 are found at all elevations from the sea-coast1 to the height of about four hundred feet1 but not higher4 ,these clay beds are very recent1 and were deposited when the surface was four hundred or five hundred feet lower than it now is2 and this amount of elevation has left the existing lakes scattered over the surface4,c ,c ,it is remarkable that on the shores of the great lakes there are certain plants the proper station of which is the immediate neighborhood of the ocean1 as if they had constituted part of the early flora of those regions when the lakes were filled with salt water1 and have survived the change that has taken place in the physical conditions of their soil4--,torrey's ,flora of the ,state of ,new ,york4 ,illustration3 ,fig4 #eh4 ,the following 7,fig4 #eh7 exhibits ,europe as it was during the ,silurian epoch1 and ,fig4 #ei as it was at the commencement of the tertiary epoch4 ,the land1 as it then existed1 is represented by the white surface1 the present waters by the dark shading1 and the land which has been reclaimed from the ocean by elevation since those periods by the lighter shading4 ,illustration3 ,fig4 #ei4 ,the whole southern part of ,south ,america1 embracing an area equal to that of ,europe1 has been elevated within a very recent period2 and some parts of it1 if not all of it1 are still rising4 ,the shells found on the plains from ,brazil to ,terra del ,fuego1 and on the ,pacific coast1 at a height of from one hundred to thirteen hundred feet1 are identical with those now inhabiting the adjacent seas4 ,and besides the organic remains1 there are1 in very many parts1 marks of erosion1 caves1 ancient beaches1 sand-dunes1 and successive terraces of gravel1 all which must have resulted from the action of the waves at a period not remote4 ,at ,lima1 articles of human skill peculiar to the original inhabitants of ,peru were found imbedded in a mass of sea-shells eighty-three feet above the present sea level4 ,the elevation on the ,pacific coast has been in part by sudden uplifts of a few feet at a time2 but it is found1 from time to time1 that there has been a change of level1 amounting to a foot or more in a year1 when there have been none of these sudden movements4 ,a considerable portion of ,europe1 reaching from ,north ,cape in ,norway to near the southern part of ,sweden1 more than a thousand miles1 and from the ,atlantic to ,st4 ,petersburg1 more than six hundred miles1 has been rising at the rate of about three feet in a century1 for at least two centuries1 and probably much longer4 ,this change is proved by the occurrence1 at considerable elevations above the sea1 of shells now found in the ,baltic2 by rocks once sunken1 now raised above the surface of the sea1 and by ancient seaports having become inland towns4 ,to determine the truth by actual measurement1 the ,royal ,academy of ,stockholm1 about thirty-five years since1 caused marks to be cut in the rocks along the coast1 to indicate the ordinary level of the water4 ,this is easily ascertained1 as the ,baltic is nearly a tideless sea4 ,the present level of the sea1 compared with that indicated by the marks before mentioned1 leaves no doubt that the country is rising4 #c4 ,the ,subsidence of ,land4--,elevations can be shown to have taken place by fossils1 and by other evidences of former sea levels which are left on the surface2 but depressions leave but few indications of change of level4 ,it is yet doubtful whether the depression is equal to the elevation2 that is1 whether the amount of land remains nearly constant1 or whether there has been an augmentation of the dry land within the tertiary and recent periods4 ,we are certain that the augmentation1 if any1 has not been equal to the elevation1 for subsidences to a great amount are known to have taken place4 ,there are occasional instances of submerged forests seen at low tide1 at some distance from the shore4 ,there are several near the coast of ,england and ,scotland1 and near the coast of ,massachusetts4 ,they are but a few feet below low water1 and do not indicate a subsidence of more than about twenty feet4 ,numerous instances are on record of the sinking down of wharfs and buildings near the sea during earthquakes4 ,almost every violent earthquake is accompanied by a change of level4 ,the changes of this kind which have been noticed are in seaport towns1 because greater facilities are there afforded for detecting them1 and because loss of property awakens attention to them2 but there is every reason to suppose that these changes of level extend to great distances both into the country and into the sea4 ,illustration3 ,fig4 #fj4 ,an immense area in the ,indian and ,pacific ,oceans1 probably ten millions of square miles1 is undergoing change of level4 ,the lines ,a ,b and ,d ,g 7,fig4 #fj7 represent nearly the axes of depression2 while an intermediate and two exterior parallel lines would represent axes of elevation4 ,the evidence of these changes is found principally in the peculiarities of the wall of coral rock encircling the islands4 ,the following figures represent1 in sections1 modifications of form of the same island4 ,the coral wall built up around the island by the polyps1 from the depth of fifty1 or at most of a hundred feet1 is shown at c c 7,fig4 #fa74 ,if the island is elevated1 this wall becomes a fringing reef 7,fig4 #fb71 b' becoming the level of the sea1 and the animal begins a new wall at the same depth as before4 ,but if the island is gradually sinking1 the wall is kept built up to the surface1 and becomes a barrier reef 7,fig4 #fc74 ,a channel is thus left between the island and the reef1 which1 though gradually filling up with broken coral or other sediment1 is generally deep enough for a ship-channel4 ,if the island continue to subside till it disappears1 and the coral wall is still kept at the surface1 it then becomes an atoll1 a circular coral island 7,fig4 #fd71 often of many leagues in diameter1 beaten by the surf on the outer edge1 but enclosing a quiet lake1 which communicates only by occasional channels with the ocean4 ,illustration3 ,fig4 #fa4 ,illustration3 ,fig4 #fb4 ,illustration3 ,fig4 #fc4 ,illustration3 ,fig4 #fd4 ,the islands contiguous to the lines ,a ,b and ,c ,d 7,fig4 #fj7 are uniformly atolls1 or are surrounded by barrier reefs1 and are therefore subsiding2 while the islands at a distance from these lines are surrounded by fringing reefs1 which indicate that they are rising4 ,a well-authenticated instance of gradual subsidence is that of ,greenland4 ,the entire western coast1 from its southern extremity to ,disco ,island1 a distance of six hundred miles1 has for the last two centuries been slowly subsiding4 ,the dwelling-houses and places of worship built by the early ,european settlers are now in part or entirely submerged4 ,the natives are said to be aware of the subsidence1 and never build their huts near the sea4 #d4 ,we have thus seen that both elevation and depression may take place4 ,there is reason to believe that these changes of level have1 in some cases1 been several times repeated4 ,in one of the eastern ranges of the ,andes1 opposite to ,chili1 there is a mass of marine strata of five thousand feet in thickness4 ,about the middle of the series there occurs a silicified forest4 ,in one place a clump of coniferous trees was found of more than fifty in number1 and a foot or more in diameter4 ,the base of the strata must have been twenty-five hundred feet below the surface of the sea1 in order to admit of the deposition of the first half of it4 ,it was then elevated1 so that a forest grew upon its surface4 ,it was then depressed at least twenty-five hundred feet1 more1 to admit of the deposition of the subsequent strata1 and the whole is now uplifted to form a mountain range of eight thousand feet in height4 ,illustration3 ,fig4 #fe4 ,the temple of ,jupiter ,serapis1 near ,naples1 in ,italy1 was built near the sea1 about eighteen hundred years ago4 ,it was gradually submerged1 and finally lost by the deposition of sediment nearly to the top of the columns4 ,it was afterwards elevated1 so as to be entirely above the level of the sea4 ,the remains of the temple 7,fig4 #fe7 were afterwards discovered by the columns projecting a little above the ground4 ,the sediment was removed to the depth of forty-six feet1 when the workmen came to the base of the columns1 and to a pavement seventy feet in diameter4 ,in #ahjg an artist was employed to take drawings of the ruin4 ,the pavement was then above the level of the sea4 ,sixteen years afterwards the same artist found the pavement covered with water1 and the depth has continued to increase since that time4 ,it is considered that for the last forty years the depression has been three-fourths of an inch a year4 ,instances enough have now been given to show how extensively the system admits of change4 ,they are sufficient to justify us in searching for indications of great revolutions in past times1 even where no such indications have as yet been discovered4 ,they will serve as a key to many otherwise inexplicable phenomena1 ,in order to the interpretation of such phenomena readily1 we must cease to look upon these as exceptional cases1 and regard them not only as facts1 but as facts of frequent occurrence4 ,from the examples which have now been given1 as well as from speculations upon the cause of these changes1 it seems highly probable that all the surface of the solid portion of the earth1 whether land or the bed of the sea1 is undergoing changes of level4 ,it may be so gradual that in the life of an individual it would be imperceptible1 even where the best means of detecting it exist4 ,these means are generally the works of man1 and they are themselves so liable to change1 that it would be scarcely possible to detect variations of level1 which amount to but a few inches in a century4 ,if we admit that the relations of land and water have always been variable1 it is impossible to arrive at any certain conclusion as to the amount1 position or form1 of the dry land at any former period4 ,we may determine1 with some degree of certainty1 what portions of the present continents were submerged at particular epochs4 ,thus1 we may infer that most of this country was submerged during the silurian period1 from the great extent of the ,silurian rocks2 and1 from the limited extent of the chalk formation in this country1 we know that during the cretaceous period most of the continent was above the surface of the sea4 ,but we have absolutely no data for determining what portions of the bed of the sea were at any time dry land4 ,it is supposable that the land has been principally confined to the equatorial regions at one period1 and to the polar at another4 ,at still a different period the land may have existed as islands scattered through a general ocean4 ,these relations may1 therefore1 be assumed to have existed1 if there are geological phenomena which best accord with such relations4 ,,section ,,iv4--,,changes ,,on ,,the ,,surface ,,of ,,the ,,earth4 #a4 ,the principal changes of this class consist in the wearing down and removing immense quantities of the surface rock4 ,the form in which the igneous rocks1 of which the entire crust of the earth was originally composed1 now appear1 furnishes no assistance in judging of the amount of denudation which they have suffered4 ,we can judge only from the amount of rock for which they have furnished the materials1 and these are the whole sedimentary series which exist both as dry land and as the bed of the sea4 #b4 ,the sedimentary rocks have also been subject to great denudation2 and we often have1 in what is left1 some indications of how much has been removed4 ,one of these indications consists in the now level surface of those portions of country in which large faults exist4 ,by the excavations for coal1 in ,england1 faults have been discovered of five or six hundred feet4 ,at the time that they were formed1 the surface must have presented precipitous escarpments 7as represented by the dotted lines in ,fig4 #ej7 of a height equal to the dislocation2 but the whole is now reduced to a general level 7z z71 denuding causes having removed the elevated portions4 ,the extent of valleys will often give some idea of the amount of denudation to which a region has been subjected4 ,in the north-west of ,scotland there is a succession of hills of about three thousand feet in elevation1 consisting1 for the upper two thousand feet1 of horizontal strata of old red sandstone4 7,fig4 #ff47 ,we cannot conceive that these mountain masses were deposited in their present isolated form4 ,the whole intervening spaces must have been filled with strata continuous with those by which the elevations are formed4,d ,d ,i entertain little doubt that when this loftier portion of ,scotland1 including the entire ,highlands1 first presented its broad back over the waves1 the upper surface consisted exclusively1 from one extremity to the other1 of a continuous tract of old red sandstone2 though1 ere the land finally emerged1 the ocean currents of ages had swept it away1 all except in the lower and last raised borders1 and in detached localities where it still remains1 as in the pyramidal hills of ,western ,rosshire1 to show the amazing depth to which it had once overlaid the inferior rocks4--,miller1 ,old ,red ,sandstone1 p4 #bb4 ,illustration3 ,fig4 #ff4 ,illustration3 ,fig4 #fg4 ,a somewhat similar instance occurs in the ,connecticut river sandstone1 in the central part of ,massachusetts4 ,the following figure 7,fig4 #fg7 represents two mountains of #a the sandstone1 between which the ,connecticut river flows4 ,the dotted lines indicate a depth of one thousand feet of the rock which has been swept away4 ,it is also thought that a bed of equal depth has been removed from this section southward1 through the ,state of ,connecticut1 to the sea-coast4 #c4 ,valleys1 and even many of the larger valleys1 are produced by the wearing down of the surface4 ,the lower portion of the ,connecticut valley is one of denudation1 though in its upper part it is a valley of elevation1 resulting from the upheaval of the ,green and ,white ,mountains4 ,the water-courses from the mountains are transverse to the direction of the ranges1 and generally consist of valleys of denudation4 ,these valleys were no doubt originally fractures1 produced while the mountains were rising4 ,the fractures have been subsequently widened by denudation into valleys4 ,illustration3 ,fig4 #fh4 #d4 ,the rocky surface1 beyond the fortieth parallels of latitude1 and in the vicinity of glacier-producing mountains1 is generally covered with grooves and stri 7,fig4 #fh71 varying from several inches in depth to the finest perceptible lines4 ,rocks that are of a soft consistence1 or which have been long exposed to atmospheric agents1 seldom exhibit these marks1 though there are probably few places1 outside of the parallels before mentioned1 where the rocky surface1 if it has been protected from atmospheric decay1 does not contain such grooving4 #e4 ,another change at the surface consists in the formation of a soil2 that is1 of a superficial layer1 of no great thickness1 of earthy matter1 a large proportion of which is always in a minutely divided state4 ,in some instances it is common sediment1 unsolidified2 in others1 it consists of the surface rock in a state of disintegration2 but a large part of the soil within the region where the grooved surfaces are found consists of materials transported from a distance4 ,soils are distinguished according to their predominant minerals1 as siliceous1 aluminous and calcareous4 ,if siliceous matter is in excess1 it will be a light1 warm soil1 and allow the water to pass through it too freely4 ,if the clay predominates1 the soil is cold1 stiff1 and too retentive of moisture4 ,a proper admixture of these three ingredients constitutes the best soils4 ,there are some other mineral ingredients essential to the productiveness of soils1 but they are always in small proportion4 ,in addition to the inorganic part which is common to the upper soil1 and the subsoil1 there is required1 in order to render the upper layer productive1 a large admixture of decaying animal and vegetable matter4 ,,section ,v4--,,changes ,,of ,,climate4 ,our means of determining the climate of any former period consists in a comparison of the fossils of such period with the existing forms of life in warm and cold climates4 ,the earliest abundant vegetation consisted principally of ferns1 rushes and mosses1 and a larger growth was attained than is attained by any of the allied forms of the present time4 ,we may infer that the circumstances under which these lower forms of vegetable life are now produced in the largest proportion1 compared with other forms1 and under which they grow to the largest size1 are the circumstances approaching most nearly those under which the early vegetation was produced4 ,these circumstances are found to be a position elevated but little above the level of the sea1 a humid atmosphere1 and the highest terrestrial temperature4 ,such facts favor the conclusion that during the coal period an ultra-tropical climate prevailed1 and that the land existed in the form of low islands1 thickly set in a general ocean4 ,the peculiar characters of some of the animal fossils1 from the earliest fossiliferous to the tertiary series1 indicate that a warmer climate prevailed during their formation than now exists4 ,the remains of marine animals1 such as the cephalopoda1 are found in great numbers and in high latitudes1 in a fossil state2 but similar species1 as the nautilus1 now abound only between the tropics4 ,the same is true of the crinoidea4 ,coralline limestone is also found in great abundance and in high northern latitudes2 but the stone-producing coral now exists only in very warm seas4 ,the remains of saurian reptiles are numerous in the olite and ,wealden2 but all the larger recent species of the lizard tribe1 such as the crocodile1 are confined to the warmer regions of the earth4 ,a former warm climate in ,siberia is indicated by the occurrence there of the remains of elephants4 ,these animals were so abundant that their tusks are now collected as an article of commerce4 ,the abundance and high state of preservation of these remains seem to preclude the explanation that they were conveyed there1 from the present tropical regions1 by any great geological convulsion4 ,the species must therefore have inhabited the country1 though the elephant is now found only between the tropics4 ,the ,siberian elephant was a different species from any now existing1 and1 unlike the recent species1 had a covering of coarse hair4 ,there is1 however1 no reason to conclude that it could endure a continued low temperature2 and its sustenance would have been impossible1 from the very stinted vegetation which that region now affords4 ,we must therefore suppose that ,siberia enjoyed1 at the period when it supported these animals in such abundance1 a tropical climate4 ,most of the facts which go to prove a change of climate have been observed in the northern hemisphere2 but the explorations in ,south ,america and ,new ,holland furnish ground for believing that the geological phenomena of the two hemispheres are essentially alike1 and that the indications of climate are the same for the same periods4 ,such is1 in general1 the evidence in reference to climate2 and it leads to the conclusion that a highly tropical climate prevailed in the temperate1 and for some distance1 at least1 into the polar zones1 in the early geological periods2 while there is no reason for supposing that the tropical regions experienced a temperature too high for physical life to endure it4 ,the climate of the earth was characterized then by a higher temperature than now1 and by greater uniformity4 ,this was the climate1 with perhaps a gradual reduction of temperature1 till the later portions of the tertiary period4 ,before the close of the tertiary period1 a change occurred1 and probably a rapid one1 to a more rigorous climate than now exists4 ,the destruction of the elephant in ,siberia was evidently sudden1 and was followed by extreme cold2 for the animals are in some cases entirely preserved in ice1 and in so perfect a state that1 when the ice which surrounds them becomes melted1 the flesh is devoured by carnivorous animals4 ,there are occasionally found1 in the drift of the boulder period1 shells similar to those of the ,arctic regions1 and in a condition to show that they have not been transported4 ,the clay beds of the northern portion of the ,united ,states and of ,canada were deposited during the last depression of that portion of the continent1 and they contain the remains of marine animals identical in several instances with species now living1 but confined to more northern regions4 ,it must therefore be admitted that the interval between the middle tertiary and the modern era was one of great cold4 ,it is generally referred to as the ,glacial period4 ,very considerable local changes of climate have also occurred within the historical period4 ,thus the mean temperature of the ,alps has been so reduced that the ancient passes have in modern times become choked up with snow1 and other passes have been sought1--a result1 perhaps1 of additional upheaval4 ,it would seem that ,siberia is now receiving a milder climate4 ,the ice in which elephants have for centuries been imbedded has been slowly melting for at least thirty years4 ,,section ,,vi4--,,advantages ,,resulting ,,from ,,geological ,,changes4 #a4 ,the division of the general surface into land and water1 as well as the diversified form of the land1 the existence of mountains and low lands1 and the consequent modifications of climate1 the waterfalls1 and the river-systems1 constituting the drainage of continents1 are all results of the process of upheaval4 #b4 ,a large part of the mineral substances employed for architectural and economical purposes are oceanic deposits1 such as the marbles1 slates1 sandstones and mineral salt1 and would have been inaccessible if they had not been elevated from the position in which they were formed4 ,and the elevation of them above the bed of the sea would have exposed only the superficial layer1 if they had not been either irregularly uplifted1 as at e c 7,fig4 #fi71 or unequally worn down1 as at b4 ,illustration3 ,fig4 #fi4 ,the granitic rocks1 as they were formed below the aqueous rocks1 must have remained unknown and useless1 if they had not been brought to the surface1 as at c1 by the most convulsive efforts of nature of which we have any knowledge4 ,thus1 natural mechanical forces have effected for man what the mechanical forces under his control would be entirely insufficient to accomplish4 #c4 ,it is by changes of this kind that we become acquainted with the geological structure of the crust of the earth4 ,mining operations have never extended to a greater depth than three thousand feet1 while the inclined position of the strata exposes for examination1 along their outcropping edges1 e a c1 the whole series1 even to the primary rocks4 ,the upheaval of the granitic rocks1 and the removal by denudation of the overlying deposits1 shows us the crystalline character which the earthy materials take1 when subjected to pressure and cooled from fusion with extreme slowness4 ,thus we have1 exposed to observation1 the process of nature in the formation and modification of rocks for several miles in depth4 ,of the central portions1 however1 including by far the largest part of the mass of the earth1 we have no knowledge whatever4 #d4 ,springs1 and the other means of obtaining water for domestic purposes1 depend in part upon the inclined position of strata1 and the broken and uneven condition of the surface1 and in part upon the alternation of permeable and impermeable strata4 ,if all the strata were porous1 like the sandstones1 the water which falls upon the surface would gradually settle through them to the level of the sea2 or1 if they were all impermeable1 like the clays1 the water would pass over the surface1 and be collected in lakes or the ocean4 ,as it is1 the porous structure of the soil and of some rocks acts as a reservoir1 from which the water is gradually discharged1 and the intervention of impermeable strata prevents its taking a perpendicular direction downwards4 ,thus1 if the stratum e b 7,fig4 #fi7 consists of porous rock1 and the one below is impermeable1 the water which is absorbed at e will appear at b as a spring4 ,or1 if the line a d is a fracture1 the water received at c may reappear as a spring at a4 ,if the strata were perforated by boring at e till the porous stratum a is reached1 the water will rise to the surface1 constituting an ,artesian well4 ,an ordinary well consists of an excavation continued till a stratum is reached which is permanently saturated with water4 #e4 ,most of the metallic ores which occur in the stratified rocks1 with the exception of iron1 are found in fractures or as dikes4 ,without these disturbances of the strata1 the ores would have remained either sparingly diffused throughout the adjacent strata1 or as a part of the melted mass at the volcanic centres4 ,the ores and metals which are found in the primary rocks are accessible only by the bringing up of these rocks to the surface4 ,the fracturing1 displacement1 and elevation of the strata1 attended1 as is often the case1 with the destruction of property and of the life both of man and the inferior animals1 might1 at first view1 be thought an unnecessary1 if not a wanton infringement upon arrangements already established4 ,but the results which we have noticed1 though by no means a full enumeration of the advantages resulting from geological changes1 are sufficient to show that even the more violent disturbances to which the crust of the earth has been subjected constitute an important part of that series of adjustments which has rendered it a suitable abode for human beings4 ,these changes are therefore neither useless nor accidental1 but are essential parts of a wise and beneficent system4 ,,chapter ,,iv4 ,,of ,,the ,,causes ,,of ,,geological ,,phenomena4 ,an exhibition of the composition and structure of the earth1 together with an account1 as far as there is reliable evidence1 of the modifications which they have undergone1 has been the object of the preceding chapters4 ,they are mainly a collection and classification of observed facts4 ,no reference has been made to causes or modes of operation1 except in a few cases where it was necessary in order that a statement or description1 might be intelligible4 ,if the facts have been given with sufficient clearness and detail to convey a correct general idea of the crust of the earth1 we are prepared to inquire what are the agencies employed1 and how they have operated in producing it4 ,it is the province of the geologist to question every known power in nature1 and to ascertain what geological effects each one is now producing2 and1 observing what effects are produced by given causes1 he is to judge of the causes which have produced like effects in past geological periods4 ,some of these causes are in their nature limited1 and effects can be referred to them only within those limits4 ,thus1 the congelation of water expands it by a certain proportion of its volume1 and beyond that it can have no effect4 ,but the expansive power of steam varies with the temperature2 and hence the effects referred to it may be equally varied4 ,thus1 we are not to expect exact uniformity of results in all past times1 but the results will vary only as the circumstances vary upon which the operation of these causes depends4 ,geological causes1 in most instances1 operate with extreme slowness2 and therefore it will require a series of observations1 continued for a long time1 to ascertain what are the capabilities of these causes4 ,but a single instance of their effects proves their capabilities thus far4 ,hence1 one instance of the deposition of a stratum of salt in a salt lake2 of the filling of a fracture with fluid lava2 of a volcanic eruption1 like that of ,iceland in #aghc2 of the subsidence of a volcanic mountain1 as that of ,papandayang in ,java2 or of the rising of a large area of land1 as in ,sweden1 as fully proves that natural causes exist capable of producing these effects1 as if the effects were produced daily4 ,as these effects increase in number1 and careful observations are made and authentic accounts preserved1 the means of correctly explaining geological phenomena will increase4 ,the causes thus far known are ,atmospheric ,causes1 ,chemical ,action1 ,organic ,agency1 and ,aqueous1 ,aqueo-glacial and ,igneous ,action4 ,,section ,i4--,,atmospheric ,,causes4 ,the oxygen of the atmosphere is capable of uniting with some of the constituents of rocks1 by which their cohesion is weakened or destroyed4 ,this is the cause of the rapid disintegration of some varieties of granite4 ,the protoxide of iron which they contain is converted1 by contact with the atmosphere1 into the peroxide4 ,its volume is thus increased1 and portions of the rock are separated from the mass4 ,when granite or limestone contains sulphuret of iron1 the oxygen of the atmosphere1 in connection with moisture1 combines with the sulphur1 forming sulphuric acid1 by which limestone and the felspar of granite are rapidly decomposed4 ,hence1 a rock which contains an oxide or sulphuret of iron should not be used for architectural purposes4 ,carbonic acid is another constituent of the atmosphere which operates as a decomposing agent4 ,the water that falls from the atmosphere is charged with it1 and thus becomes capable of dissolving calcareous rocks4 ,carbonic acid is thus indirectly the means of the rapid destruction of rocks of this class4 ,it is also believed that carbonic acid enters into direct combination with some of the constituents of rocks1 and particularly felspar2 for it is found that in those countries where carbonic acid issues in great quantities from the earth1 the rocks1 especially those which contain felspar1 disintegrate rapidly4 ,masses of many tons' weight1 which appear to be solid granite1 after being broken are found to be in such a state of decay that fragments may be reduced to sand between the fingers4 ,the moisture of the atmosphere has some effect as a decomposing agent4 ,rocks which are exposed to frequent alternations of moisture and dryness soon crumble into fragments4 ,rain1 falling upon the surface of rock1 produces1 mechanically1 a destroying effect1 which is not to be overlooked4 ,variations of temperature1 especially those alternations above and below the freezing point1 have greater influence than any other cause in the destruction of rocks4 ,when the water with which a rock is saturated congeals1 the resulting expansion tends to enlarge the interstices1 and thus to separate the particles of the rock4 ,when the ice melts1 the particles fail to resume the closeness of arrangement with which they were before packed4 ,by frequent repetition of this action1 the superficial portion loses its cohesion1 and disintegrates4 ,it is also found that in the region of perpetual snow the surface of the mountain masses is covered with rock in a disintegrated or fragmentary state1 in greater abundance than below the snow line2 but no explanation of this fact has yet been found4 ,in mountainous regions1 electrical discharges and violent storms have some destroying effect4 ,winds have considerable power in changing the place of earthy matter in a disintegrated state4 ,in deserts1 the sands are carried in great quantities to great distances4 ,the causes now enumerated1 when considered separately1 and as acting for only limited periods of time1 seem hardly worthy of notice2 but when considered as operating conjointly1 and for indefinite periods of time1 they must have produced important changes on the surface of the earth4 ,from these causes1 the surface and ornaments of castles and other ancient edifices1 and of boulders1 and all insulated rocks1 are found to be decayed1 and often to a considerable depth4 ,it is from these causes that a soil is produced on every surface of rock which is not so exposed to the action of currents that the debris is removed as fast as it is formed4 ,hence it is1 also1 that a slope of detritus is formed at the base of every declivity1 so that the ledge appears only at the highest points4 ,it is from a combination of these atmospheric causes that a large part of the sediment is furnished which brooks and rivers carry away4 ,and when cohesion is not entirely overcome1 it is so far weakened that other causes are much more effectual than they would otherwise be1 in effecting the disintegration of rocks4 ,,section ,,ii4--,,chemical ,,action4 ,all those changes in which the action is molecular1--that is1 between the molecules as such1 and not between the masses1--including the effects of the imponderable substances1 we regard as resulting from chemical agency4 ,under the control of these molecular forces the crystalline rocks have taken their form2 and if the crust of the earth could have remained in a fixed condition1 in which these forces would have been in equilibrium1 no further chemical action could have taken place4 ,but1 instead of being in a fixed condition1 the present system is one of perpetual change4 ,various disturbances of this equilibrium of forces1--such1 for instance1 as the diurnal and annual changes of temperature at the surface1 and the still greater secular changes of temperature at great depths1--will bring the chemical forces into operation4 ,the mechanical disintegration of the crystalline rocks1 and the deposition of them in strata independently of the chemical affinity of their particles1 will give occasion for chemical changes1--that is1 for a rearrangement of the particles in accordance with their affinities1--whenever any movement of the particles among themselves can take place4 ,these movements take place1 to a very great extent1 under the influence of electrical currents1 and of change of temperature1 even while the masses retain their solid form4 ,chemical affinity has exhibited itself on the largest scale in the formation of the various mineral species of which the crust of the earth is composed2 but we may also refer to the same cause the formation of divisional planes in rocks1 the concretionary arrangement1 and mineral veins4 #a4 ,divisional ,planes4--,it has before been stated1 that the older rocks1 in many cases1 cleave freely in planes not parallel with the stratification4 7,see ,fig4 #dh47 ,in some instances1 in beds of lava1 a similar cleavage exists1 sufficiently perfect to allow of its use as a roofing material4 ,in these cases1 there must have been a rearrangement of the particles1 so that their axes of greatest attraction would lie in parallel planes2 the same arrangement which exists in mica and other crystalline substances1 which have one and but one free cleavage4 ,a similar arrangement has sometimes taken place under such circumstances as to submit the process to more careful scrutiny4 ,in the gold mines of ,chili1 the powder from which the gold has been washed is thrown into a common heap4 ,a great deal of chemical action then commences2 salts of various kinds effloresce on the surface1 and the mass becomes hard1 and divides into fragments which possess an even and well-defined slaty structure4 ,when a portion of clay1 worked into a paste with a very weak acid1 is submitted to a weak voltaic action for several months1 and then dried1 it is found to have acquired a distinct though imperfect cleavage structure4 ,it appears1 then1 that both electrical currents and ordinary chemical action are capable of arranging the particles of an earthy mass into separable layers4 ,we may then regard this change in the older rocks as an imperfect crystallization1 and probably induced by electro-chemical agency4 ,it is also found that all rocks are divided into huge blocks by seams not parallel with the cleavage1 and too regular to be considered as fractures4 ,these seams bear an analogy to the secondary faces of crystals1 which are never parallel to the cleavage4 #b4 ,concretionary ,formations4--,there exist in many rocks concretions which differ from the mass of the rocks4 ,in most of the tertiary clays there are small concretionary nodules1 which contain more calcareous matter than the mass of clay around them4 ,in the coal formation1 the nodular iron ore consists of concretionary masses4 ,in the chalk formation1 nodules of flint abound1 and generally in layers4 ,in many of these cases1 particularly in the clays and coal1 the nodules have an organic nucleus1 and1 although concretionary1 they retain the marks of stratification of the adjacent rocks4 ,hence they could not have been deposited in the form of nodules4 ,there must therefore have been in the rock1 though in the solid state1 such motion among the molecules that particles of a particular mineral have separated from the mass and rearranged themselves in concretionary layers1 yet so gradually as not to disturb the lines of original stratification4 ,illustration3 ,fig4 #gj4 ,there are other instances1 similar to the last in all respects1 except that the segregated portion does not take the concretionary form4 ,when gypsum is distributed in small proportion through a formation1 there seems very little reason to doubt but that it is1 by a molecular action1 segregated from the strata in lenticular masses1 as at a 7,fig4 #gj74 ,many of the limestone strata contain irregular aggregations of quartz4 ,it is presumed that the siliceous and calcareous matter was deposited together as sediment1 and that the aggregation has resulted from a movement among the particles similar to that by which the concretionary structure is produced4 ,the columnar structure of basalt seems to have resulted from a peculiar molecular action1 at first resembling a concretionary arrangement1 while the mass was cooling from a state of fusion4 ,in experimenting to ascertain the cause of this structure1 ,mr4 ,watt fused in a furnace seven hundred pounds of basalt4 ,when cooled1 he found that numerous spheroids had been formed1 and that when two of them came in contact1 they did not penetrate each other1 but were mutually compressed and separated by a well-defined plane1 invested with a rusty coating4 ,when several met1 they formed prisms4 7,fig4 #ga47 ,illustration3 ,fig4 #ga4 #c4 ,mineral ,veins4--,the phenomena of veins are such that they cannot all be referred to the same cause4 ,in some1 the vein-stuff has been protruded as a dike1 differing from ordinary dikes only in the accidental circumstance that it contains a metal or a metallic ore4 ,mineral veins are not1 however1 generally filled by injection from below4 ,it is found that those veins only are productive which have an east and west direction4 ,but injected dikes run in all directions4 ,the ore often varies in richness at different depths in the vein1 or passes into ore of some other metal4 ,the ore also varies in kind and quality1 according to the character of the rock through which the vein passes4 ,these phenomena are best explained by supposing that the sediment of which the strata were formed contained the mineral substances of these veins in small proportion4 ,after they were solidified1 and fractures had been formed1 the mineral substance was transferred by molecular action to the fissures1 and deposited4 ,it was shown by the early experiments of ,davy1 that voltaic currents are capable of taking up mineral substances from their solutions1 and removing them from one cup to another4 ,it has been ascertained that in most mineral veins a proper apparatus will detect the existence of electric currents4 ,it may be regarded as certain1 that the unequal heating of different parts of the surface at the same time1 by the sun1 causes a vast current of feeble intensity to circulate around the earth once in twenty-four hours4 ,the unequal distribution of heat below the surface may also produce currents subject to other laws4 ,we should expect that these currents would take up the mineral substances diffused through rocks1 and deposit them by themselves4 ,it seems probable1 therefore1 that the molecular action1 from which the segregation of metallic veins has resulted1 was that of voltaic currents4 ,,section ,,iii4--,,organic ,,causes4 ,the effects of all organic causes in producing geological changes are inconsiderable1 compared with those of inorganic causes4 ,with the exception of the coral formation1 the most important of these effects are those produced by human agency4 ,we find examples of this agency in the distribution of animals and plants beyond the regions where they are indigenous2 in the increased numbers of certain species1 and in the diminution1 if not extinction1 of others2 in the modifications of climate1 dependent on the destruction of the forests and the cultivation of the soil2 in controlling the course of rivers2 in arresting by embankments the encroachments of the sea2 in breaking up and changing the place of great quantities of rock by mining and engineering operations2 and in the increased quantity of sediment furnished to streams by cultivating the surface1 and thus preventing the protecting influence which the matted roots of trees and the smaller vegetables would otherwise have4 ,such effects1 though attributable mainly to man1 are produced in some degree by all other animals4 ,besides these general effects1 it is the existence of organic forms that has conferred on all the sedimentary rocks their fossiliferous character4 ,the records of the climate of each geological period1 of the physical geography1 of the vegetable productions1 and of the animal forms by which the earth was peopled1 consist in the remains of the living beings of these several periods1 imbedded in the contemporaneous rock formations4 ,but in the sediment deposited since the human era there must have been furnished both the remains of human beings and works of art1 such as implements of labor and war1 pottery1 coins1 fragments of ships1 c4 ,moreover1 the quantity of material which has been furnished by organic causes is by no means small4 ,the coal-beds are the product of vegetable growth exclusively4 ,we not unfrequently find strata of great extent consisting almost entirely of the shells of molluscous animals1 of the stems of encrinites1 or of the shields of microscopic animalcules4 ,but the most abundant rock which can be regarded as the product of animal organization is the coral formation4 ,it consists of immense walls of coral limestone1 separating either an atoll or the land of an island or continent from the open sea4 ,the base of this wall has a width varying from a hundred feet to a mile or more1 and the outer edge of it is at such a distance from the shore as to give a depth not much exceeding a hundred feet4 ,over this area of the bed of the sea1 which forms the base of the wall1 the coral polyp commenced its work4 ,attaching itself in immense numbers over this area1 it deposits calcareous matter from its under surface1 and thus1 by degrees1 elevates itself towards the surface of the water1 till it reaches a level a little above low-water mark4 ,the height of the wall would not1 with these conditions1 exceed one hundred feet2 but some hundreds of the islands surrounded by coral walls are gradually subsiding4 ,the depositions of the polyps keep pace with the subsidence1 so that this wall has reached an elevation from its base of a thousand feet1 and in one instance of two thousand feet4 7,see ,figs4 #fa1 #fb1 #fc1 #fd47 ,most of the islands of the torrid zone are thus surrounded with coral reefs1 except a few where the cold polar currents reduce the temperature too low to admit of their growth4 ,in one instance1 along the north-east coast of ,new ,holland1 there is a coral reef1 some twenty-five miles from the land1 which has a continuous extension1 excepting occasional inlets of no great depth1 of a thousand miles4 ,the reef along the island of ,new ,caledonia is four hundred miles long4 ,a large number of other reefs have a nearly equal extension4 ,there is thus an area of several thousands of square miles covered to a great depth with this coralline limestone4 ,some limestone formations of great extent among the older rocks were the work of similar animals4 ,these lower forms of organization have1 therefore1 always been important geological agents1 both in collecting the carbonate of lime from its solution in the waters of the ocean1 and in depositing it as solid rock4 ,,section ,,iv4--,,aqueous ,,causes4 ,water is1 next to heat1 the most important geological agent4 ,all the stratified rocks are aqueous deposits1 and their total amount is in some respects a measure of the influence which this agent has exerted4 ,the materials have been obtained from the destruction of prexisting rocks1 transported by water1 and deposited in layers4 ,when the first strata were formed1 the sediment must have been obtained entirely from igneous rocks1 because only those rocks existed2 but now it is obtained from every kind of rock which is exposed to abrading or decomposing agencies4 ,hence1 many of the later formations contain fragments1 and sometimes within the fragments well-characterized fossils1 of earlier formations4 ,the sediment which is ultimately to become stratified rock is deposited on the beds of the ocean1 and other great reservoirs of water4 ,the formation of most of the aqueous rocks1 therefore1 as well as of the igneous rocks1 is deep below the surface2 and neither of these operations1 on the large scale1 is directly exposed to our observation4 ,we may1 however1 learn by observation1 how the sediment is furnished to the waters and transported by them1 and we can form some correct ideas of the manner in which it will be laid down on the bed of the ocean1 and solidified4 ,i4 ,the ,furnishing of ,sediment4 #a4 ,almost all the minerals which occur in the geological formations are1 to some slight extent1 soluble in water4 ,hence1 rain water1 by passing through a stratum of earth or rock and reppearing as a spring1 loses the insipidity which it had as pure water1 and becomes palatable4 ,it is then found to hold in solution some small proportion of earthy substances1 upon which this change of taste depends4 ,although the proportion of dissolved matter is very small1 yet the surface of earth upon which this distilled water is shed is one-fourth of the surface of the globe1 and solution below all that surface is constantly taking place4 ,no inconsiderable amount must thus have been furnished1 from the existing rocks of each period1 towards the formation of the strata of a later period4 ,there are some substances which are soluble in water1 in large quantities4 ,rock-salt is an example4 ,it is not found in any very large proportion in rocks generally1 but a very large aggregate amount has been taken up by the waters which have filtered through the strata4 ,the ocean gathers into itself1 by degrees1 all the soluble substances which are thus taken up4 ,it receives supplies of water charged with these substances from springs1 rivers and lakes4 ,it returns as much water as it receives2 but it is always in the form of vapor1 and is therefore pure water4 ,hence the saline properties of the ocean1 and of those inland seas which have no outlets4 ,there is thus gathered the materials for the rock-salt deposits4 ,but many substances which are not considered soluble in water become so by some modification of the water4 ,water of a high temperature is capable of dissolving silex4 ,in ,iceland and other volcanic regions1 the hot springs are charged with silex1 which is deposited as the water cools4 ,thus1 siliceous formations accumulate around springs of this kind4 ,the various agates may have been deposited from such solutions4 ,in the decomposition of mica1 felspar and volcanic rocks1 a considerable amount of potassa is set free4 ,potassa or soda renders the water in which it is dissolved capable of dissolving silex in large quantity4 ,in these ways water removes1 with some degree of rapidity1 one of the most insoluble minerals which rocks contain4 ,in volcanic countries1 and in coal districts1 carbonic acid is abundant1 both in spring-water and in the gaseous form4 ,water charged with this gas becomes capable of dissolving limestone4 ,where the water is exposed to the air1 the gas gradually escapes1 and the calcareous matter is deposited4 ,many accumulations of this kind are now taking place4 ,some have already extended several miles in length1 and they are often of great thickness1 in one instance1 in ,italy1 two hundred feet 7,fig4 #gb74 ,it is also probable that many calcareous springs issue below the surface of lakes and seas1 and thus1 both fresh-water and marine deposits would now be forming4 ,these formations are distinctly stratified1 and are white and crystalline1 and become solid at the time of deposition4 ,illustration3 ,fig4 #gb4 ,these dissolved materials are less observed than others1 because they do not render the water turbid2 but there is reason to believe that several of the aqueous formations1 particularly the limestones1 have been built up chiefly from them4 #b4 ,the abrading action of rivers furnishes considerable detrital matter4 ,the general form of the river courses is determined by other causes than the agency of the river itself1 yet a river which has a rapid current is continually deepening its channel4 ,we have proof of this by observing1 when the water is low1 that irregularity of surface which running water always produces1 by wearing away the softer parts of the rock1 and leaving the harder in relief4 ,hence1 a river will have its rapids either where the hardest strata occur1 and which therefore wear down least rapidly1 or where the rock has been hardened by the intrusion or near proximity of dikes4 ,the abrading power of rivers occasionally becomes greatly increased by waterfalls4 ,the force which the water acquires in its descent is such as to excavate a deep cavity at the foot of the fall1 reaching back under the ledge from which the water descends4 ,the ledge is therefore constantly being undermined4 ,the cataract of ,niagara is peculiar1 in having the rock at its base of a soft and friable texture1 so that it is rapidly worn away1 while the upper rock is a compact siliceous limestone4 ,if the order of superposition had been the reverse1 the falls would have been converted into a series of rapids4 ,it is now preserved as a single fall1 and as such it has probably cut the gorge1 about two hundred feet deep and seven miles in length1 through which its waters now reach ,lake ,ontario4 ,a few years since1 a large mass1 perhaps half an acre in area1 fell from the centre of the horse-shoe fall4 ,another mass of equal size has recently fallen from the western extremity of the ledge4 ,thus the fall is gradually receding4 ,but the foreign substances1 such as drift-wood1 ice1 sand and gravel1 with which the waters of a river are occasionally charged1 contribute more than everything else to its abrading power4 ,at such times its volume is generally greatest1 and its current the most rapid4 ,its bed is then sometimes perceptibly deepened and widened in a few hours4 ,much the greater part1 however1 of the earthy matter which rivers convey in such quantity to the ocean1 is furnished by other means than the eroding action of the river itself4 ,it is the loose material1 the soil and alluvium1 to which the solid rocks have been reduced by the imperceptible but incessantly operating atmospheric agencies1 from which most of the sediment of rivers is obtained4 ,after a rain1 every tributary rivulet is turbid with suspended earthy matter1 and it is from these sources that the larger streams receive the most of their sediment4 ,some observations have been made for the purpose of ascertaining the quantity of sediment which rivers annually carry into the sea4 ,the ,kennebec furnishes materials which1 if spread evenly on an area of one mile square1 and consolidated into rock of the specific gravity of granite1 would have a thickness of six inches4 ,the ,merrimac furnishes about two-thirds as much1 the ,ganges about two hundred and fifty times as much1 and the ,mississippi two thousand times as much4 ,thus1 the tendency is1 to reduce the highest parts of the land1 and to fill up the depressions of the sea2 and though we have not data enough to form any reliable estimate of the total annual discharge of sediment into the ocean by rivers1 yet they are sufficient to show that the effects of this kind are on a large scale1 and to relieve us from any impression that existing agencies are inadequate to the production of the stratified rocks4 #c4 ,the action of waves is another means by which detrital matter is furnished4 ,wherever the shore consists of loose materials1 and is favorably situated to be acted upon by the waves1 there is annually a sensible encroachment of the sea4 ,such encroachments are rapidly making in many places2 and thus a large amount of sediment is delivered to the waters of the ocean4 ,the waves also encroach upon the coast when it consists of rocks1 even of the most indestructible kinds4 ,they continually beat upon it1 undermine the cliffs1 and precipitate them into the sea4 ,the tides increase the power of the waves1 by varying the place of their action1 so as to present the same surface of rock alternately to the action of water and of the air1 frost and sun4 ,during storms1 the waves have sufficient force to break off fragments of rock from the escarpment1 sometimes in masses weighing twenty tons or more1 and remove them many rods inland4 ,a bold1 rocky coast always exhibits evidence of a great amount of erosion4 ,the steep escarpments and the high rugged shafts of rock 7,fig4 #gc7 against which the waves now beat are the remnants of masses of rock which once extended further into the sea1 but have been worn away by the waves4 ,it is by such agency that the deep inlets and harbors of the coast of ,new ,england and ,nova ,scotia have been excavated4 ,illustration3 ,fig4 #gc4 ,this more violent action of the waves is only occasional2 but when of less power1 they are incessantly rolling the loosened fragments of rock upon each other1 and thus wearing them down to particles small enough to be carried away by the water4 #d4 ,the action of waves is confined to the coast1 and never extends to great depths4 ,but marine currents act principally on the bed of the sea4 ,the temperature of the mass of the ocean is much higher in the equatorial than in the polar regions4 ,at the surface1 the difference amounts to sixty degrees4 ,the waters of the torrid zone are thus expanded1 and flow over the colder waters of the north and south2 while these colder waters of the polar seas flow back1 in an under current1 towards the equator4 ,for the same reason1--a difference of temperature1--there will be1 in the higher regions of the atmosphere1 a current of warm and moist air flowing from the equator north and south1 while the cold and dry air conies in from the polar regions towards the equator4 ,in this way the equatorial waters are carried1 in a state of vapor1 towards the poles1 where they are condensed1 and go to increase the currents of water moving towards the equator4 ,such are the general causes of the oceanic movements in a north and south direction2 but these currents at once become deflected westward1 by the diurnal revolution of the earth1 as the trade winds do4 ,hence there results a ,pacific equatorial current1 which has a motion of about thirty miles a day1 and an ,atlantic equatorial current1 moving from sixty to seventy miles a day4 ,the principal marine currents are shown in ,fig4 #gd4 ,the currents moving towards the poles are superficial1 and therefore do not produce any marked geological effects4 ,but the polar currents1 and those which are produced from them1 are of great depth1 and there is no reason to suppose that they do not move1 from their commencement1 along the bed of the ocean4 ,there is also reason to suppose that they exist at great depths1 where the opposing superficial currents entirely conceal them4 ,wherever these currents come to the surface1 their motion is undoubtedly greater than it is at the bottom1 where it is retarded by the friction which the moving waters encounter1 and by the irregularities of the bed of the ocean4 ,it should1 however1 be remembered1 that they move with the weight of the whole superior body of water2 and therefore1 though the motion be very slow1 it will still possess great power4 ,any irregularities in the bed of the ocean beneath such a current must be subject to very rapid abrasion4 ,we shall sea hereafter1 that earthquake vibrations often shiver the rocks at the solid surface2 and if any of these ridges at the bottom of the ocean were thus acted upon1 the loosened portions would be swept away by the current and deposited at lower levels1 or where the current subsides4 ,if1 in any instance during an earthquake convulsion1 a fault should be produced across one of these marine currents1 like the great fault of over five hundred feet in ,england1 the abutment thus thrown up would soon be worn down2 and if it consisted of unconsolidated matter1 it would be swept away almost bodily4 ,illustration3 ,fig4 #gd4 ,the effect of such currents will be greatest where they are deflected by a continent or island4 ,thus1 a marine current sets from near ,new ,holland in a direct line to the north of the island of ,madagascar1 where it is arrested by the ,african coast1 and deflected into the narrow ,mozambique channel1 and there acquires a velocity of four or five miles an hour4 ,it is impossible that any kind of rock should receive the constant force of such a body of water without being rapidly worn away2 and1 if there should be any difference of texture in this rocky barrier1 the softer portions would yield the most rapidly1 and thus valleys might be formed4 ,it is not improbable that the deep indentation on the western coast of ,africa may have been due1 in a great measure1 to the coast current from the ,cape of ,good ,hope2 and that the ,caribbean ,sea and the ,gulf of ,mexico may have been excavated by the force of the ,atlantic equatorial current being thrown into this angle4 ,we may regard these currents as oceanic rivers2 and it is obvious that the volume of the terrestrial rivers would bear no comparison with that of these currents1 and their effects would be equally small in the comparison4 ,the ,gulf ,stream1 and the ,mozambique and other similar currents1 must be wearing down the valleys through which they flow1 to such an extent as to furnish an immense amount of detrital matter for the formation of new rocks4 ,it is principally to the agency of these deep marine currents that we are to refer those extensive denudations1 so abundant on the present continents1 such as the wearing out of the intermediate masses of rock between the hills already referred to 7,fig4 #ff71 the denudation of the ,connecticut river sandstone1 and1 perhaps1 the excavations which have formed ,lake ,erie and ,lake ,ontario4 ,,ii4 ,the ,transportation of ,sediment4 ,the detrital matter obtained in these several ways is swept away by running water4 ,the specific gravity of rocks does not1 in general1 exceed two and a half4 ,hence1 to keep them suspended in water1 will require a force of only three-fifths of what would be necessary to suspend them in the atmosphere4 ,in the case of river currents1 the velocity and irregularity of motion are generally sufficient to keep all the finer sediment equally distributed4 ,there will1 however1 be a division of the sediment according to the strength of the current4 ,hence1 the bed of a mountain stream1 if there is any loose material1 always consists of pebbles4 ,as it approaches the alluvial region1 the bed is sandy2 and when the current becomes very sluggish1 it consists of a fine mud4 ,rivers never deposit all their sediment1 some of them none of it1 along their course4 ,large rivers continue partially distinct from the ocean water to a considerable distance beyond their mouths4 ,the waters of the ,amazon have been recognized at a distance of three hundred miles4 ,this depends in part upon the volume and velocity of the river2 more1 however1 upon the fact that river water is lighter than sea water4 ,this extension of a river will1 in most cases1 be sufficient to deliver a part of its sediment into a marine current4 ,when such a current sweeps very near the mouth of a river1 as it does to that of the ,niger1 the ,amazon1 or the ,mississippi1 it is probable that most of its sediment is carried away by it4 ,the transporting power of a marine current is greater than that of a river1 in consequence of the greater specific gravity of its water2 but it has scarcely any of that irregular motion of rapid rivers1 upon which their transporting power in a great degree depends4 ,the force of the current alone1 when it reaches the bottom1 is1 however1 sufficient to remove every form of loose earthy matter4 ,thus it may be presumed that the ,gulf ,stream sweeps all the sediment from its bed until it reaches the latitude of ,cape ,hatteras1 where the cold waters from the north begin to underlie it1 and it takes the character of a surface stream4 ,but the transporting power of marine currents depends mostly upon the depth of water4 ,it is found1 by experiment1 that ordinary river sediment will sink in water about one foot in an hour4 ,a current1 therefore1 of a thousand feet in depth1 which moves a mile in an hour1 would carry its sediment a thousand miles4 ,it is obvious1 then1 that there is no part of the bed of the sea which may not be receiving sediment4 ,,iii4 ,the ,deposition of ,sediment4 ,from what has been said of the weight of sediment1 it follows that it will be deposited whenever the water in which it is suspended is at rest4 ,hence1 when a river increases in breadth so as to form a lake1 the waters at the outlet are seldom turbid4 ,the earthy matters with which the principal and tributary streams were charged all settle to the bottom1 and go to lessen the capacity of the reservoir4 ,thus lakes are continually diminishing in depth and area4 ,in many instances1 they are already filled with sediment1 and are thus converted into alluvial plains1 through which the river flows in a narrow channel4 ,it is frequently the case that a river1 as it approaches the sea1 has so slow a motion that its sediment is deposited on the bed of the stream4 ,thus the bed will be raised1 and the banks will also be raised1 by the deposition of sediment upon them at periods of overflow4 ,the river will then be raised above the adjacent country4 ,the river ,po1 for the last part of its course1 is from ten to twenty feet above the adjacent lands4 ,the same is true of the ,mississippi1 and many other rivers4 ,the streets of ,new ,orleans are several feet below the surface of the river4 ,in an uninhabited country1 such a river would soon seek a new and lower channel2 but in a populous country1 it becomes a matter of interest and safety to confine the river in its old channel1 by artificial embankments4 ,but the principal part of the sediment of rivers is conveyed to the sea4 ,it here mingles with the debris which the waves have furnished1 and a part of it is deposited to form deltas4 ,the remaining part is taken up by marine currents1 mingled with the debris which they have furnished1 and is spread out on the bed of the ocean4 ,of the extent of these deposits we can form no estimate4 ,those of rivers and lakes are comparatively unimportant1 as they are in the older formations4 ,some of the delta deposits are already of great extent4 ,that of the ,ganges contains an area of twenty-six thousand square miles1 that of the ,niger twenty-five thousand1 and that of the ,nile twelve thousand4 ,the delta of the ,rhone has increased its area by three hundred square miles in the last thousand years4 ,the ,po has encroached upon the ,adriatic two thousand square miles in the last two thousand years1 and the ,mississippi has enlarged its delta by one hundred square miles in the last hundred years4 ,in the deep valleys of the ocean accumulations may be taking place on as large a scale as they ever have been in former times4 ,,iv4 ,character of the ,formations thus produced4 ,sedimentary matter thus deposited would take the form of strata4 ,thus1 a delta deposit may receive at one time from a river a layer of coarse gravel and pebbles1 and in the course of a few hours the current may be so reduced that it will convey to the same place only fine sand and silt4 ,or1 if a depositing current receive its sediment only at intervals1 the heaviest particles would be thrown down first1 and the more finely levigated particles would continue to fall1 till the water became transparent4 ,another supply would furnish another similar stratum1 and so on4 ,the same arrangement might result from the sediment being furnished by different rivers4 ,thus1 if sediment were furnished to the ,gulf ,stream by the ,merrimac river1 and the streams emptying into the ,bay of ,fundy1 the freshets would occur earlier in the season in the ,merrimac1 and it would furnish a supply of sediment from a region of primary rocks4 ,a later supply would come from the red sandstone region of ,nova ,scotia1 and the stratification would be indicated by the different kinds of rock produced4 ,thus stratification will result from difference in the color1 composition1 or size of the particles of which rocks consist4 ,a great variety of causes1 both general and local1 may therefore give to a deposit this character4 ,hence1 as stratified rocks are produced by the sediment now laid down from water1 we may conclude that the older stratified rocks are the sediment deposited in like manner1 in former times4 ,the occurrence of layers of different composition1 as one way in which the stratification is indicated1 is produced by local and frequently recurring causes4 ,there are1 however1 other alternations of much greater extent2 those1 for example1 nearly twenty in number1 distinguished by striking differences in lithological character1 into which the ,new ,york system of rocks is divided4 ,these alternations have resulted from more general causes4 ,the physical geography of a wide region must have been so different1 at the different periods during which these several formations were deposited1 as to change1 at each period1 the kind of sediment furnished to the forming currents1 and modify the types of animal life4 ,we have seen that the same causes that determined the stratified arrangement will determine the alternations of strata of coarse and fine materials4 ,it is obvious that the stratification of the marine deposits will be nearly horizontal4 ,if the surface were very irregular upon which the deposition commenced1 the irregularity would constantly diminish2 for the movement of the water over this surface1 however slow1 would tend to remove the accumulations from the highest points1 and leave them at the lowest 7,fig4 #ge74 ,delta and lake deposits will1 however1 dip somewhat1 though never at a high angle1 towards the deep water4 ,in certain situations1 where a river and a tidal wave1 coming in conflict1 cause1 in succession1 eddies and currents in opposite directions1 we should expect to find the stratification very irregular 7,fig4 #gf72 sometimes false stratifications 7a b71 sometimes the strata cut off abruptly1 and at other times contorted or dipping in opposite directions within short distances4 ,illustration3 ,fig4 #ge4 ,wherever sediment is deposited1 it will entomb whatever of the remains of animal or vegetable life may be mingled with it4 ,they will be at once protected against the influence of all the ordinary decomposing agencies1 and will continue for ages to retain their peculiar markings1 and even their colors4 ,they will thus constitute1 in all future time1 a record of the present condition of the organic world4 ,the lacustrine deposits can contain only fresh-water species of animals1 marine deposits only marine animals1 while deltas may contain the remains of marine life mingled with those which have been washed down by rivers4 ,the remains of birds1 insects1 and terrestrial animals1 may occasionally occur1 in every kind of deposit4 ,sediment deposited in deep water will never contain fossils in abundance1 the deep parts of the ocean being almost wholly destitute of animal or vegetable life4 ,it is only in water of a few fathoms that the greater number of species and of individuals occur4 ,in all these particulars the deposits now forming sustain a close resemblance to the older formations4 ,illustration3 ,fig4 #gf4 ,there are certain formations1 as that of the coal1 which required conditions for their formation different from those of ordinary sedimentary deposits4 ,coal consists of mineralized vegetable matter4 ,its vegetable origin is proved by the uniform occurrence of vegetable fossils almost exclusively in the coal measures4 ,when reduced to thin slices and examined under a high magnifying power1 a structure very similar to the ligneous tissue of existing conifer is sometimes found to exist4 ,there are probably vegetable deposits now taking place not altogether unlike those which produced the coal measures4 ,we know that many rivers--the ,mississippi1 for example--now carry into the sea great quantities of ligneous matter4 ,before the country was inhabited by man1 the quantity was undoubtedly much greater than it now is4 ,it floats for a time2 but the ligneous tissue itself is heavier than water1 and as soon as the air is excluded from the pores1 and they are filled with water1 it will sink4 ,the woody and earthy matters are swept into the sea together2 but1 as they sink under different circumstances1 they will be deposited separately4 ,thus wood may continue to accumulate in particular places in the sea for long periods1 with but little intermixture of earthy substances4 ,it is1 however1 to be expected that1 in the progress of geological changes1 the places which at one time receive deposits of wood will at another receive detrital matter1 and thus the wood will become deeply buried beneath sedimentary strata4 ,wood thus situated will become converted into coal4 ,trees which had been covered to considerable depth with earth have been found near the ,mississippi river changed to lignite1 a substance resembling charcoal4 ,in this case1 the wood had been exposed to no greater heat than is common to the crust of the earth at the depth where it was found2 and yet it had undergone this change since the country has been known to ,europeans1 as it retained the marks of the axe when it was discovered4 ,it has also been found by experiment that vegetable matter1 by long submersion in water1 passes into the state of lignite4 ,this is the first step in the conversion of wood into mineral coal4 ,when lignite is exposed to moderate heat and great pressure1 it loses the characters of lignite1 and becomes mineral coal4 ,this is shown by facts observed in ,germany1 ,ireland and ,iceland1 where beds of lignite have been overspread by basalt4 ,the upper portions of the lignite are changed to mineral coal4 ,the lower portions1 which the heat did not reach1 retain the characters of lignite4 ,beds of vegetable matter1 with a great thickness of rock deposited above them1 would therefore be subject to all the conditions necessary to convert them into coal1 namely1 pressure from the superincumbent mass1 and the heat which the strata uniformly assume at great depths4 ,it is not improbable1 therefore1 that coal-beds are now forming1 and that they have been formed at every geological period since an abundant terrestrial vegetation commenced4 ,accordingly1 there occurs in ,virginia an extensive coal-field in the olite formation4 ,coal-fields also occur in ,england1 of less extent1 in the same formation4 ,in ,france1 and other parts of ,europe1 there are extensive beds of lignite in the tertiary formation4 ,we have therefore no difficulty in accounting1 in a general way1 for the formations of the carboniferous period4 ,the vegetables were probably less woody than those of the present time of equal size1 and were therefore more easily prostrated and committed to the waters4 ,they grew rapidly in moist ground1 and perhaps in shoal-water1 and required an atmosphere charged with moisture and of a high temperature4 ,thus much is inferred from the conditions most favorable for the growth of recent species analogous to the coal-plants4 ,these recent species are tropical plants1 and grow in moist insular situations1 conditions which would have existed at the carboniferous period1 if the present coal-fields were then an archipelago dotted with low islands4 ,such being regarded as the origin of the coal-beds1 the alternations of the earthy and carbonaceous strata may be referred1 provisionally1 to those great changes in physical geography upon which the other alternations of strata on a large scale depend4 ,but the regularity with which the coal-seams and sandstone succeed each other presents some difficulties which1 in the present state of knowledge1 we cannot satisfactorily account for4 ,beds of salt occur1 interstratified with other rocks1 in nearly all countries4 ,still1 it is not a sedimentary deposit1 and its formation must depend upon peculiar circumstances4 ,in ,new ,york1 saline1 together with earthy matter1 constitutes the ,onondaga limestone1 one of the formations of the ,new ,york system4 ,in ,kentucky1 the strata of rock-salt are in the coal formation2 in ,england1 they are in the new red sandstone2 in ,spain1 they are in the greensand1 and in ,poland they are in tertiary strata4 ,the conditions of its formation have therefore existed in connection with the deposition of every fossiliferous rock4 ,it has been shown that the ocean is the principal reservoir of the saline matters which are taken up whenever water percolates through rocks4 ,it must happen not unfrequently1 in the course of submarine elevations1 that a basin of sea-water will be cut off from its communication with the sea2 and from this basin the evaporation might be more rapid than the supply of water4 ,the great salt-lake of ,utah is undoubtedly a basin of this kind4 ,the ,mediterranean ,sea is another such basin1 not yet wholly separated from the ocean4 ,the evaporation exceeds the supply of water from the rivers1 and a powerful stream is therefore continually thrown in from the ocean1 through the ,strait of ,gibraltar4 ,the waters of the ,mediterranean are already more highly charged with salt than ordinary sea-water4 ,this sea may ultimately become a saturated solution1 and begin to deposit salt4 ,but whether it does1 or not1 it indicates the way in which salt-beds may be formed4 ,v4 ,solidification of ,aqueous ,deposits4 ,sediment is generally deposited as a soft mud1 but in nearly all the older formations it has become solidified4 ,when rocks are deposited from a chemical solution1 they take at once the solid form4 ,such is the case with rock-salt and with limestone1 when the material has been held in solution4 ,solidification takes place in nearly the same way when water which holds carbonate of lime or oxide of iron in solution filters through beds of sand or gravel4 ,the substance held in solution is deposited in the interstices till they become filled1 and the whole is changed to solid rock4 ,some rocks are composed of such materials that they set1 like hydraulic cement1 when they are deposited4 ,other rocks become solid simply by drying4 ,thus a deposit now forming in ,lake ,superior becomes1 by drying1 nearly as hard as granite4 ,such a deposit will therefore become solid whenever it shall be elevated above the water4 ,the pressure to which all but the upper layers are subjected is probably sufficient to reduce most rocks to the solid state4 ,dry and pulverized clay is reduced by artificial pressure1 for a moment1 almost to stone4 ,the pressure upon the deep-seated rocks is constant1 and greater than any artificial pressure can be4 ,in addition to these causes1 all the older rocks have been subjected to a high temperature1 some of them nearly to that of fusion4 ,by this means the solidification of every kind of rock would be promoted1 and probably some may have been reduced by it to the solid state1 which would otherwise have remained as an incoherent mass4 ,,section ,v4--,,aqueo-,,glacial ,,action4 #a4 ,glaciers4--,a glacier is a mass of ice occupying the bed of a mountain valley1 having a slow progressive motion1 and reaching somewhat lower in the valley than the line of constant snow4 7,fig4 #gg47 ,the ,glacier des ,bois1 which may be regarded as a specimen of the ,alpine glaciers1 covers an area of about seventeen square miles4 ,in its lowest portion1 when all its branches have become united into one stream1 it has an average width of half a mile1 and is five miles long4 ,it is estimated that the glaciers of the ,alps cover an area of fourteen hundred square miles4 ,these have been the most carefully studied1 though glaciers are found in the valleys of various other ranges of mountains4 ,in the higher valleys1 the snow1 which falls at all seasons of the year1 accumulates in immense quantities1 and the steep mountain sides contribute1 by frequent avalanches1 to this accumulation4 ,the snow1 when thus increased1 does not become a compact1 adhesive mass2 but1 changing into particles of solid ice1 it resembles sand rather than snow4 ,it is this nv which constitutes the upper part of every glacier1 and which1 in a modified form1 constitutes the lower part4 ,the valleys descend rapidly towards the base of the mountains2 and this snow-ice1 having no cohesion between its particles1 moves slowly down the slope of the valley1 like a very imperfect liquid4 ,after descending below the line of perpetual snow1 the surface will melt during the day2 and the water1 sinking into the porous mass1 becomes frozen1 and converts the whole into more or less compact ice1 yet never into a rigid mass4 ,influenced by its own weight1 and by the pressure of the snow-ice behind1 it still continues its motion1 and conforms itself to the shape and curves of the valley through which it passes4 ,the average movement per annum may be stated at about five hundred feet4 ,the temperature of the rocky bed of the valley will be a little1 and but a little1 higher than thirty-two degrees4 ,there will therefore be but little melting at the bed of this river of ice4 ,as it receives continual accessions from the atmosphere1 it will therefore increase in volume till it descends to the level of perpetual snow4 ,below this line the waste exceeds the addition2 and as it approaches the lower and cultivated portions of the valley1 it rapidly diminishes1 till it finally loses the solid form1 and becomes a rivulet4 ,the terminus of the glacier is determined principally by the general climate of the country4 ,any considerable variation of climate will cause it to recede1 or descend lower down the valley4 ,the terminus varies1 however1 somewhat with the seasons1 being lower in winter than in summer1 though the motion is much less in the cold season than in the warm2 and it descends many rods further some seasons than it does others4 ,the glacier consists principally of snow1 more or less modified in structure2 but it also contains whatever else may have been thrown upon its surface1 or into the snows by which it is fed4 ,tributary glaciers extend up through all the gorges into which the irregular surface of the mountain-top is divided4 ,on these rough peaks there are always fragments of rock1 varying in size from fine sand to masses weighing many tons2 some of them loosened when the mountain was upheaved1 some by subsequent earthquake vibrations1 and others still by tempests1 lightnings1 and changes of temperature4 ,when the snow has accumulated to a certain extent on the steep slopes1 it falls in avalanches into the valleys1 carrying with it loosened masses of rock1 and often breaking off large fragments from the rocky escarpments against which it strikes4 ,these avalanches are almost constantly descending1 and hence a glacier always contains considerable earthy matter distributed through it4 ,illustration3 ,fig4 #gg4 ,the friction of the glacier1 at its edges and along its bed1 separates more or less of the rock over which it moves2 and hence there is always a layer of mud and pebbles under the glacier1 and a line of loose fragments1 called a lateral moraine1 at the sides4 ,when two glaciers unite1 the two lateral moraines1 thus brought together1 come to the surface1 forming a medial moraine1 and show the line of junction sometimes for miles4 ,the friction of the glacier on the bed of rock1 assisted by the layer of pebbles1 will wear down the prominent portions1 and everywhere polish the surface4 ,fragments of rocks may be frozen into the glacier at all depths4 ,those which lie near the lower surface of the glacier would1 by slight melting of that surface1 project downward so as to act as a graver's tool on the rock over which it passes4 ,hence1 when the extremity of the glacier has receded beyond its ordinary limit1 the surface of rock exposed is found1 upon examination1 to be polished1 striated1 and occasionally grooved an inch or two deep4 ,since the waste is almost wholly superficial1 earthy matter1 which was at first concealed in the mass of the glacier1 is continually coming to view1 as the surface melts and runs off4 ,thus1 none of the freight of the glacier is left along its course1 but all is carried to its terminus and discharged there4 ,hence1 at the lower extremity of the glacier there is always an embankment of earth1 pebbles1 and boulders4 ,if the glacier recedes a few yards at one season of the year1 and leaves its earthy fragments scattered over this surface1 they will be pushed forward into a ridge1 as the glacier again advances4 ,this ridge is called a terminal moraine1 and consists wholly of substances which have been separated from the mountain mass1 often at the highest beginnings of the glacier4 ,at the terminus of all the ,alpine glaciers1 there is a series of these moraines 7a a a1 ,fig4 #gg7 marking the successive limits of the glacier in former times4 ,there is a ridge of boulders on the north side of the ,swiss valley1 near the base of the ,jura ,mountains1 resembling a terminal moraine4 ,these boulders consist of several groups1 distinguished by peculiarities of structure and composition2 and each group lies opposite to the particular ,alpine valley which now furnishes the same kind of fragments4 ,it has been thought that1 at a former period of more severe climate1 the ,swiss valley was filled in part with ice1 and that the present glaciers extended across it to the ,jura ,mountains4 ,it is found that the polished and striated surfaces of the rocks in the ,alpine valleys are precisely like the surface of the rock1 which has not been exposed to atmospheric influences1 in the north of ,europe and ,america4 ,it has been proposed to extend the glacier theory1 and account for these phenomena by supposing that the north polar regions were1 at the ice period1 capped with a glacier-mass1 extending as far south as the drift phenomena appear4 ,it is not to be doubted that the phenomena of polished surfaces and transported materials in the immediate vicinity of the ,alps1 and near other high mountains1 are correctly referred to glacial action4 ,this theory has therefore solved1 in part1 one of the most difficult problems in geology2 but there is great difficulty in extending it so as to account for the drift phenomena in general4 ,if the motion depends upon gravitation only1 the origin must have a much greater elevation than the terminus1 which would not be the case in the great glacier supposed to extend southward from the ,arctic regions4 ,elevation of temperature1 it has been thought1 might account for the movement of the mass southward4 #b4 ,icebergs4--,in very high latitudes1 the ice1 which makes out from the land into the sea during the cold season1 suffers but little waste at any time4 ,this sheet of ice continues to increase in breadth and thickness1 by congelation1 from year to year4 ,the spray and the snows of each succeeding year will also add to the mass4 ,it thus accumulates to the height of several hundred yards4 ,it will also reach down a good many feet below the surface of the sea1 and will extend back on the land1 or lie heaped up against a precipitous escarpment1 and firmly frozen to it4 ,after a certain amount of extension over the sea1 the accumulated weight of the ice and snow would tend to depress it1 and break it loose from the shore4 ,the waves would tend to the same result1 and would act at greater mechanical advantage1 as its extension from the shore becomes greater4 ,hence1 it would ultimately become separated from the shore1 and float in the water4 ,at its commencement1 the earth1 pebbles and rocks1 which may lie along the shore1 and as far down into the sea as the congelation extends1 are frozen into it4 ,in many situations its mass would be increased by avalanches while it remained attached to the land1 and these would supply also masses of earth and rocks1 as they do to glaciers4 ,when it becomes loosened from the shore1 it will break off1 and carry with it some of the earthy portions of the coast1 or the less firmly fixed masses of rock from the escarpment against which it formed4 ,thus every iceberg becomes freighted1 more or less1 with earth and rocks4 ,this has almost uniformly been found to be the case1 when they have been landed upon by ships' crews and examined4 ,we have seen that the general tendency of the waters of the ocean1 and of the lower stratum of the atmosphere1 is to a motion from the poles towards the equator4 ,however irregular1 therefore1 the course of an iceberg may be1 its general movement1 influenced both by the prevailing winds and by ocean currents1 will be towards the equator4 ,illustration3 ,fig4 #gh4 ,these floating ice-mountains 7,fig4 #gh7 are formed in great numbers1 and of vast size4 ,the relative specific gravity of ice and water are such that nine cubic feet of ice1 below the surface of water1 will support one cubic foot above it4 ,as icebergs are often one or two hundred feet high1 their vertical depth must be a thousand feet at least2 and their area is equal to a square mile1 and sometimes it is much greater4 ,in #ahdj1 the ,united ,states ,exploring ,expedition1 in the extreme southern ocean1 coasted for eighty miles along a single iceberg4 ,they are never absent from the polar seas2 and at certain seasons they are so abundant along the usual course of vessels from ,new ,york to ,liverpool1 as greatly to obstruct and endanger navigation4 ,an iceberg may continue for some time to increase in size1 while floating in the polar seas1 but will at length reach a latitude where the waste will exceed the additions1 in consequence of the temperature both of the air and of the water4 ,it will1 therefore1 drop gradually the earthy matters which it contains1 upon the bed of the ocean4 ,it is not improbable that icebergs may often reach down so far as to strike the highest points of the bed of the sea4 ,the ice would be lifted1 and glide over the elevation1 without suffering any perceptible deviation from its general course4 ,it would thus affect the surface of rocks exactly like a glacier4 ,if1 however1 the iceberg becomes permanently stranded1 and melts in one place1 its earthy matters will be thrown down upon the elevation which first arrested it4 ,if the bed of the sea1 between the fortieth and sixtieth degrees of latitude1 could be exposed for examination1 the rocky surface would be found to be polished and striated by the icebergs which have passed over it1 and the whole surface would be strewed with boulders and drifted materials brought from ,arctic and ,antarctic lands4 ,sometimes it would be accumulated in heaps1 and sometimes spread nearly over the surface4 ,we have seen that very recently1 probably about the close of the tertiary period1 the portion of ,europe and ,america over which the northern drift is found1 has been depressed several hundred feet4 ,it may be presumed that at that time icebergs floated over it1 polished the surface of the rocks1 and distributed the boulders and other drift which is now found upon it4 ,,section ,,ii4--,,igneous ,,causes4 ,i4 ,of the ,temperature of the ,mass of the ,earth4--,heat has been the most efficient agent in determining and modifying the structure of the earth2 and1 in order that the explanations of the phenomena referable to this cause may be intelligible1 some idea must be formed of the actual present condition of the mass of the earth with respect to heat4 ,at any point of the surface there are variations of temperature1 depending on external causes4 ,but these variations are found to extend only a little way below the surface1--never more than a hundred feet4 ,at greater depths1 it is found that the temperature invariably increases with the depth4 ,deep mines have always a temperature above the mean annual temperature at the surface4 ,the water obtained by deep boring is always tepid when it comes to the surface4 ,the thermal springs1 so abundant in this country and in ,europe1 are so situated as to justify the impression that their waters come from great depths4 ,to make these general observations of any value1 we must determine the law by which the temperature increases4 ,the result of all the observations yet made1 in mines and upon wells and springs1 is that1 below the first hundred feet1 the temperature increases by one degree of ,fahrenheit's scale for every forty-five feet4 ,regarding this law of increment as applicable to all depths1 at ten miles below the surface we should have a temperature above that produced by the combustion of wood2 and at twenty-five miles1 a temperature of three thousand degrees1 by which nearly all mineral substances would be reduced to a state of fusion4 ,the general conclusion of a temperature sufficient to melt the mineral substances of which rocks are composed1 at no considerable distance below the surface1 is confirmed by the fact that portions of the interior of the earth--at least1 at the volcanic centres--are in a melted state4 ,the intimate connection between some volcanoes situated a hundred miles or more apart1 so that they are alternately in a state of activity and rest1 indicates that these centres are connected1--that subterranean melted lava extends from one to the other1 so that when one is active1 the elastic force is relieved at the other4 ,these deep-seated lakes of lava must therefore underlie large areas4 ,we are justified1 then1 in concluding that the mass of the earth1 with the exception of a comparatively thin superficial layer1 has a very high temperature4 ,by way of accounting for this temperature1 it is now generally assumed that the earth was originally in a state of fusion2 that it was a mass of liquid lava 7if1 indeed1 it had not a temperature sufficient to reduce it to the ariform state74 ,starting with this assumption1 there must necessarily be a gradual reduction of temperature by radiation1 and a time must arrive when the surface would be crusted over with solidified lava2 and this crust would increase in thickness as the cooling advanced1 the interior still retaining its heat and liquidity4 ,the present condition of the crust of the earth1 its form1 that of an oblate spheroid1 with the exact difference of the equatorial and polar diameters which is found to exist1 as well as the phenomena of volcanic eruptions1 will all admit of explanation on this hypothesis4 ,it has1 however1 been rejected by some2 and1 to account for the heat of the interior of the earth1 it is suggested that1 if the bases of the earths and alkalies1 particularly potassium1 sodium and calcium1 exist in their metallic state beneath the surface1 the rapid oxidation of them by the access of water would generate heat of sufficient intensity to melt the oxidized materials1 and thus account for the phenomena attributable to heat4 ,either of these hypotheses may be adopted2 but it is not necessary to account at all for the existence of this temperature4 ,the fact is susceptible of proof2 and1 though we may not be able to frame any hypothesis to account for its existence1 we may yet employ the fact in the explanation of other phenomena4 ,,ii4 ,the ,action of ,internal ,heat in producing ,volcanoes4 ,the phenomena of volcanoes and earthquakes are evidently produced by some force operating from below4 ,the effect of heat alone would be to reduce the rock to a liquid state4 ,there is no reason to suppose that it is ever sufficient to reduce them to the ariform state4 ,the elastic force must therefore depend upon some other substance associated with the lava1 and this substance is water4 ,this will be shown by an examination of lavas4 ,at the time of their ejection1 they are in a fluid or semi-fluid state2 but it is not a complete fusion4 ,even the most fluid lavas contain particles of minerals in a solid state4 ,the liquidity depends upon the fusion of the more fusible portions1 and upon the steam of water at a high temperature1 which fills the interstices between the solid particles4 ,the porous character of cooled lavas is produced by the steam which filled the cavities previous to solidification4 ,steam always escapes from the surface of a lava current while it is cooling1 and it is always discharged in immense volumes from the orifice of eruption1 in connection with the lava1 and especially at the close of an eruption4 ,the geographical position of volcanoes1 also1 leads to the conclusion that water is essential to their activity4 ,there are five principal lines of volcanic activity4 ,one1 commencing at the southern extremity of ,south ,america1 extends northward along the ,andes and ,cordilleras to ,california or ,oregon4 ,the second has a north-east and south-west direction1 from the ,aleutian ,islands through the ,kurule1 ,japanese1 and ,philippine islands1 till it meets the third line1 lying in a nearly east and west direction1 embracing ,sumatra1 ,java1 and most of the ,pacific volcanic islands4 ,a fourth band commences in the ,grecian islands1 and extends westward so as to include the volcanoes of ,italy and the adjacent islands1 and the ,azores4 ,the fifth band embraces the volcanic islands of the ,west ,indies1 crosses ,mexico in about the latitude of the city of ,mexico1 and extends into the ,pacific4 ,there are also some isolated centres of volcanic activity1 such as ,iceland4 ,these volcanic bands embrace about three hundred volcanoes4 ,it will be seen that they must nearly all be in close proximity to the ocean1 or to large seas4 ,about two-thirds of them are on islands4 ,moreover1 the volcanic vents which are wholly submarine are probably very numerous4 ,this circumstance of the position of volcanoes establishes a presumption that they cannot exist at a distance from some large body of water2 and1 taking it in connection with the constant presence of aqueous vapor in lava1 we are justified in the conclusion that the presence of water is an essential condition of volcanic activity4 ,knowing that heat and water exist at the volcanic centres1 it is not difficult to form an idea of their mode of operation4 ,the water1 diffused through the interstices of the lava1 and subjected to a temperature sufficient to melt the lava1 would possess an elastic power1 which1 though never computed1 we may well suppose capable of overcoming any resistance which the crust of the earth might present4 ,the repressing force will be the tenacity and weight of the superincumbent strata4 ,whenever the elasticity is superior to this repressing force1 it will manifest itself in the fracture of the strata1 and often in the ejection or lava to the surface4 ,this fracturing of the strata1 produced by an uplifting subterranean force1 is believed to be the cause of the noise and the vibratory motion which are the chief phenomena of earthquakes4 ,the elastic force may raise lava to the surface1 and thus the fracture would become a volcano4 ,but the force may expend itself by the discharge of vapor into the fissure1 or by merely filling it with lava4 ,in either case1 the only evidence of the existence of the volcanic force would be the noise and the wave-like motion experienced at the surface4 ,the cause of the volcano and earthquake is therefore the same1 though the phenomena which characterize them are different4 ,when the strata are is thus fractured1 lava may for a time be discharged along the whole line4 ,by the cooling of lava in the fracture1 it would become partially reunited4 ,still1 this would be the line of least resistance4 ,it would therefore be again burst through in certain places1 which would long continue to be orifices of discharge1 and thus the original fracture would determine a line of volcanic activity4 ,the repressing force may become greater at an orifice of eruption than at some other point1 either by the great accumulation of ejected materials around the opening1 or by the dormancy of the volcano long enough for the complete solidification of the lava with which the channel was filled4 ,the least resistance may then be far from any previous vent1 when a new orifice of discharge will be opened1 and a new volcano make its appearance4 ,it seems probable1 also1 that volcanoes may become extinct by the reduction of temperature at the volcanic centre1 and that new volcanic centres may be formed2 but the cause of this change of temperature is not yet well understood4 ,new volcanoes have broken out in the sea1 near ,iceland1 in several instances2 others in the volcanic line east of ,asia4 ,graham ,island1 situated between ,sicily and ,africa1 was formed by an eruption which broke out in the bed of the sea where the soundings were more than one hundred fathoms4 ,the island was at one time two hundred feet 'above the sea1 and three miles in circumference4 ,it was1 however1 gradually destroyed by the action of the waves1 and now remains a dangerous reef1 covered by less than two fathoms water4 ,the volcano of ,jorullo1 in ,mexico1 was formed in this way4 ,previous to the formation of the mountain1 the region where it now is was a cultivated table-land4 ,during the year #agei volcanic action commenced and continued1 until1 at the expiration of twelve months1 a cone had been formed having an elevation of sixteen hundred feet above the adjacent plain4 ,an orifice of eruption is at first but little elevated above the general surface2 but1 by the accumulation of ejected matter1 a cone is at length formed around the vent4 ,the upper portion of a cone always consists of these materials1 but there may also be in progress a general elevation of that part of the earth's crust1 and the cone will partake of that general elevation4 ,the cones of the ,andes owe their height1 in a great measure1 to a general movement of elevation2 those of tna and ,vesuvius1 in a greater degree1 to accumulation of ejected matter4 ,in either way1 the height may become so great that the force necessary to raise a column of lava to the top would be greater than the sides of the cone1 weakened as they always are by fractures in all directions1 can sustain4 ,hence1 the highest craters of tna and ,south ,america have long been closed1 and the lava escapes through fissures at a lower level1 and lateral cones are produced4 ,illustration3 ,fig4 #gi4 ,the form which the materials have1 when ejected from volcanoes1 depends mainly upon the degree of liquidity of the lavas at the volcanic foci4 ,if the liquidity is very perfect1 the aqueous vapor will readily rise through the lava4 ,the steam thus separated will drive before it whatever rocks1 or previous lavas1 may obstruct it4 ,in their progress they would be reduced to sand and powder1 and ejected as volcanic cinders4 7,fig4 #gi47 ,if the lava possess considerable viscidity1 the aqueous vapor will separate with more difficulty1 and the lava and vapor will ascend the channel together4 ,large bubbles of vapor will1 however1 collect with more or less of frequency2 and1 as they rise through the lava1 will drive forward a portion of it1 and cause the overflow to take place by pulsations4 ,as the bubbles reach the surface1 their bursting causes the loud reports1 which are compared to the discharge of heavy artillery4 ,with each explosion some of the lava will be projected violently into the air1 and1 cooling1 will fall to the surface as scori1--or1 if the lava be highly vitreous1 it will be drawn out into fibres1 and descend as volcanic glass4 ,,iii4 ,geological ,phenomena referable to ,volcanic ,action4 ,volcanic agency has probably never been less than it is now1 and we ought therefore to find its effects very general and important4 #a4 ,the most obvious of these effects are the fractures with which the crust of the earth is everywhere intersected4 ,the uplifting force upon which all volcanic phenomena depend would necessarily fracture the crust1 and the wave-like motion resulting from the fracture would cause numerous secondary fractures1 having a parallel direction4 ,they are often of such extent1 during earthquakes1 as to endanger life4 ,during the great earthquake at ,lisbon1 in #agee1 a fracture opened of sufficient width to swallow up the quay1 and several thousands of persons who had fled there for safety4 ,the chasm remained permanently open to the depth of six hundred feet4 ,the earthquakes with which the valley of the ,mississippi was visited in #ahaa so often fissured the surface1 that the inhabitants protected themselves by clinging to the trunks of trees1 which they felled transversely to the direction of the fissures4 ,illustration3 ,fig4 #hj4 ,the first fracture which is produced by the upheaving force will open upwards1 and scarcely reach down to the seat of the force4 ,but there will be other parallel fractures1 dependent upon the first1 and opening downward4 ,thus1 the primary fracture at a 7,fig4 #hj7 will be at once followed by the fracture b1 opening toward the lava1 which will be injected into it1 and which1 on cooling1 will form a dike4 ,their formation is mostly concealed from observation1 but not always4 ,during the eruption of tna1 in #affi1 numerous fissures opened1 one of which was six feet wide and twelve miles in length2 and the light emitted from it indicated that it was filled with lava to near the surface4 ,the process was as perfectly seen as from the nature of the case it could be4 #b4 ,the conversion of the lower sedimentary strata into metamorphic rocks has been effected by volcanic heat4 ,the material of which dikes consist has been injected in a highly-heated state2 and1 by observing the effect which they have had upon the adjacent rocks1 we may judge of the effect which subterranean heat must have upon the lower mechanical strata4 ,wherever the dikes are of considerable thickness1 they have converted the adjacent shales into primary slate1 the sandstones into quartz rock1 and the dark and friable limestones into granular marble1 and destroyed the organic impressions4 ,in the southern extremity of ,norway there is a district in which granite protrudes in a large mass through fossiliferous strata4 ,these strata are invariably altered to a distance of from fifty to four hundred yards from the granite4 ,the shales have become flinty1 and resemble jasper2 and near the granite they contain hornblende4 ,the siliceous matter of the shales has become quartz rock1 which sometimes contains hornblende and mica1 and therefore constitutes a kind of granite4 ,the limestone1 which at points remote from the injected rock is an earthy1 blue1 coralline limestone1 has become a white1 granular marble1 near the granite1 and the corals are obliterated4 ,the altered shales and limestones in many places contain garnets1 ores of iron1 lead1 c4 ,the annexed 7,fig4 #ha7 is a plan of this granite and altered rock4 ,illustration3 ,fig4 #ha4 ,one of the most instructive examples of metamorphic action in this country is found in the ,white ,mountains of ,new ,hampshire4 ,these mountains have1 till recently1 been thought to consist principally of granite2 but it is now ascertained that this supposed granite is an altered rock of the silurian period4 ,it is represented as intersected by veins of felspathic granite2 and the general mass is itself in many parts converted into a near approximation to a binary granite1 composed of distinctly developed quartz and white felspar1 with a few sparsely scattered specks of mica4 ,in its weathered surfaces it wears a close resemblance to some fine-grained granites2 but1 upon inspecting a fresh fracture with a magnifier1 we instantly perceive many rounded grains of quartzose sand1 and the felspar is imperfectly formed1 though the mica has more nearly reached the condition which it has in granite4 ,in some of the coarse varieties of this white rock1 small rounded pebbles of quartz are to be seen1 giving unequivocal evidence1 even to the naked eye1 of its being an altered sandstone4 ,we feel no hesitation in deciding it to have been a silico-argillaceous white sandstone1 now almost granitized by extensive metamorphic action4 ,similar illustrations1 on a small scale1 may be seen in every country where the strata have been cut through by intrusive dikes4 ,sir ,james ,hall has shown the same by actual experiment4 ,he exposed pulverized chalk to heat sufficient to melt it1 and under sufficient pressure to prevent the escape of the carbonic acid4 ,after cooling1 the chalk was found to have taken the form of crystallized limestone4 ,but instances enough have been given to show what changes should be looked for wherever the sedimentary rocks have been exposed to a high temperature4 ,the lower strata must have been exposed1 for long periods of time1 to such a temperature4 ,we do not know at what depth below the surface of the earth the rocks become liquid2 but above the line of actual fusion there must be a mass of rock not melted1 yet scarcely retaining the solid form4 ,for a great thickness1 perhaps for several miles1 it would be in a more or less yielding state4 ,as there is not actual fusion1 the stratification is not destroyed1 but such a degree of mobility among the particles exists1 that some degree of crystallization takes place1 and the elastic forces below easily bend1 throw into folds1 compress1 and in every way contort these strata4 ,at the same time1 any organic matters which they may contain are decomposed1 and the impressions of them are obliterated4 ,and such is the condition in which the metamorphic strata are actually found4 #c4 ,denudation is1 in a great measure1 dependent on volcanic action4 ,it results from the billowy motion peculiar to the earthquake4 ,this is not simply a violent horizontal motion1 but an equally violent vertical one4 ,it is a series of waves1--a succession of alternate elevations and depressions of the solid crust4 ,the height of these waves can only be judged of by their effects2 but it is difficult to account for some of these effects1 without supposing the waves to have been several yards in height1 and their velocity1 in the few instances in which the time has been accurately determined1 was twenty miles a minute4 ,that such earthquake waves actually exist there can be no doubt4 ,during the earthquake in ,calabria1 in #aghc1 the flagstones in many of the towns were lifted from their places and thrown down inverted1 and trees bent so that their tops touched the ground4 ,during the great earthquake in ,chili1 in #ahce1 the walls of houses1 which were parallel to the line of oscillation1 were thrown down1 while those that were at right angles to it1 though greatly fractured1 were often left standing4 ,wherever careful observations have been made1 during and after severe earthquakes1 analogous facts have been noticed4 ,persons are generally affected with sea-sickness4 ,the sea is violently agitated4 ,it often retires to an unusual distance1 and then returns upon the shore with most destructive waves4 ,incredible1 therefore1 as it may seem1 that the solid crust of the earth should be thrown into such wave-like undulations1 the fact is well established4 ,with a velocity of twenty miles an hour1 the successive waves may be some miles apart1 and yet be sufficient to account for all the phenomena4 ,it is evident1 therefore1 that the curvature of the wave will be very slight1 and yet enough to break into fragments all the rocks thus curved4 ,during the earthquake in ,chili1 before referred to1 the ground was fissured1 in many parts1 in north and south lines4 ,some of the fissures near the cliffs were a yard wide4 ,many enormous masses had fallen on the beach4 ,the effect of the vibrations on the hard primary slates was still more curious4 ,the superficial parts of some narrow ridges were as completely shivered as if they had been blasted by gunpowder4 ,similar phenomena seem everywhere to be exhibited by earthquakes4 ,it may be presumed that almost all parts of the earth have1 at different periods1 been subject to these earthquake waves4 ,accordingly1 we find that the crust of the earth is nowhere in an entire state1 but is divided by irregular lines into comparatively small fragments4 ,by this means1 the deep fissures produced by fractures opening upwards would be filled with fragments of rock shattered from the uplifted edges4 ,in this way the boulder masses were originally loosened from their parent beds1 and exposed to the action of ice1 or any other transporting agencies4 ,in the same way the rocky bed of the ocean is1 to a considerable depth1 reduced to a disintegrated mass4 ,in this condition it will be rapidly removed by marine currents1 more or less broken1 worn and comminuted1 by the movement1 and deposited elsewhere4 ,the materials have thus been furnished for a very large proportion of the sedimentary rocks1 and especially of those which are composed of distinct fragments of other rocks4 ,by this means1 also1 wherever the rock formations come to the surface1 they are so broken that limestone1 sandstone or granite1 suitable for architectural purposes1 is seldom found1 except at considerable depths4 ,this fragmentary condition of the surface rock is such as exposes it to be acted upon readily by any powerfully abrading causes1 or to be more rapidly disintegrated by atmospheric and aqueous causes4 #d4 ,we have already assumed that one principal division of rocks--the unstratified--is of igneous origin4 ,we have the proof of actual observation1 that lavas1 and the accompanying tufas and grits1 are volcanic products4 ,the peculiarities of these products1 in situation1 structure1 and form1 and in the imbedded minerals1 are so great1 that whenever we find these peculiarities in the rocks of a country not now volcanic1 we still regard these rocks as of volcanic origin4 ,we thus have lavas1 as well as stratified rocks1 of different ages4 ,there has probably been no time in the earth's history when they have not been forming4 ,the trappean rocks are also of igneous origin4 ,it is evident1 from their occurring in the form of dikes1 that they have been in a melted state4 ,as they rest upon rocks of a sedimentary origin1 they must have been thrown up by volcanic forces4 ,yet they differ from ordinary lavas4 ,they are not vesicular in their structure1 are more crystalline1 and there is in no case evidence that they have flowed from craters4 ,if we regard them as the lavas of submarine volcanoes1 we shall have conditions which will account for all their peculiarities4 ,at a certain depth the pressure of the water would be sufficient to prevent the formation and escape of vapor1 and therefore the lavas thus ejected would not be vesicular4 ,as the rapid cooling of lavas depends1 in a great degree1 upon the escape of watery vapor1 submarine lavas would cool slowly1 in consequence of the pressure4 ,the liquidity depending in part upon the retention of the heat1 and in part upon the retention of the aqueous vapor1 they would consequently remain in a liquid state much longer than the lavas of sub-arial volcanoes4 ,they would therefore take a more highly crystalline form4 ,all the loose materials thrown out during the eruption would be removed by oceanic currents1 and hence no cone would be built up around the orifice of eruption4 ,we may therefore regard the trappean rocks as the lavas of submarine volcanoes4 ,the present volcanoes of this kind are necessarily producing the same kind of rocks1 though there will be no other proof that they exist1 except the existence of the volcano1 till the bed of the sea becomes dry land4 ,the granitic rocks are also the product of igneous causes4 ,granite is the most abundant of these crystalline rocks2 and the others1 such as crystalline limestone1 are so intimately associated with granite that they must have had the same origin4 ,granite is everywhere found to send off dikes into the overlying rocks1 and must therefore have been in a state of fusion2 that is1 it must have existed as lava beneath the surface4 ,it is obvious that fluid lava always exists in great quantity beneath areas of energetic volcanic activity4 ,portions of this lava must in succession take the solid form4 ,wherever the surface is elevated along a line of fracture1 the lava which is accumulated beneath rises above the level of the general reservoir of lava1 and will therefore part with its heat more rapidly4 ,on cooling1 it becomes the granitic nucleus of the mountain4 ,we ought also to suppose that1 by the extremely slow process of the transmission of heat to the surface1 the crust of the earth is everywhere increasing in thickness2 that is1 the upper portion of the great lava mass is solidifying4 ,sir ,james ,hall has shown1 by experiment1 that earthy substances1 reduced to a state of fusion1 become more highly crystalline as they are allowed to cool more slowly1 and are subjected to greater pressure4 ,it is difficult to conceive of these conditions existing in a higher degree than they do in the cooling masses of lava below the stratified rocks4 ,these lavas must therefore take the highly crystalline form which the granitic rocks are found to have4 ,all the igneous rocks have therefore existed as subterranean lavas4 ,the volcanic rocks have become vitreous1 the granitic are crystalline1 and the trappean are intermediate in structure1 coinciding with the circumstances of pressure and rate of cooling under which they have severally been formed4 #e4 ,the ,elevation of ,mountains is another result of volcanic action4 ,the height of mountains depends1 in part1 upon general elevation4 ,yet there is a different action1 upon which the existence of the mountain1 as such1 depends4 ,whenever igneous action becomes intense under any portion of the earth's surface1 and the elastic force greater than the repressive1 the solid crust will be broken and raised up1 and along this line of fracture the lava will rise above its general level elsewhere4 ,this lava1 thus lifted out of the general mass1 in time solidifies1 and forms the nucleus of a mountain4 ,at successive periods the elevating force is renewed1 and adds somewhat to the mountain mass before supplied4 ,in this way the mountain is ultimately formed4 ,so far as observations have been made1 the elevation of mountains seems not to be gradual1 but spasmodic2 and yet the elevating force probably accumulates constantly and uniformly4 ,the repressing force consists of the weight of the strata above1 which may be regarded as constant1 and their strength1 which is variable4 ,when the elevating force becomes greater than both the repressing forces1 the crust is fractured4 ,the strength of the strata then becomes nothing1 and the repressing force is the weight alone4 ,the elastic mass below at once expands1 and the requisite space is furnished by the uplifting of the strata along the line of fracture4 ,as the ridge of lava which fills this additional space cools1 it recloses1 in part1 the original fracture1 and the repressing force again consists of the two elements1--weight and strength4 ,there will therefore be no further elevation till the elevating force is again superior to these two forces4 ,thus the elevating force1 though it may accumulate at a uniform rate1 will manifest itself only at considerable intervals4 ,as the accumulation of lava along the line of fracture is the cause of the upheaval1 every mountain must have a central granitic axis4 ,sometimes this granitic mass is pushed up through the fissure1 as in the case of ,mont ,blanc4 ,at other times1 the stratified rock1 which formed the original surface1 is carried up so as to form the surface rock nearly to the top4 ,in either case1 the strata are lifted along the line of fracture1 and left in an inclined position4 ,in this position the older rocks are always found1 wherever there has been any considerable amount of igneous disturbance4 ,in some instances1 the additional space required by the expansion of the igneous mass below is furnished1 not by the uplifting of the strata1 but by their compression into folds between two lines of upheaval4 ,the igneous rock is elevated but little above the stratified through which it had burst2 but the stratified rocks have taken the undulatory form1 and the widening of the igneous mass along the lines of fracture has compressed the undulations1 until the planes of the strata have become vertical4 ,fig4 #hb will give an idea of the successive changes by which the vertical position of the strata has been produced4 ,illustration3 ,fig4 #hb4 ,the force by which mountains are elevated being the elasticity of the vapor diffused through the subjacent lava1 it may happen1 if the lava have a high degree of fluidity1 that this vapor will collect in large masses1 and rise as far as the lava is in a fluid state4 ,the irregular flow of lava from craters during an eruption is undoubtedly due to the rapid ascent of such steam bubbles through the lava4 ,such an accumulation of vapor under a mountain mass1 if it cannot escape1 would support it as long as the temperature remained unchanged4 ,but1 upon a reduction of temperature1 the mass which had been upheaved by it would be unsupported1 and liable at any time to sink4 ,instances of subsidence on a comparatively small scale will admit of explanation in this way4 ,papandayang1 one of the loftiest volcanic mountains of ,java1 sunk down four thousand feet in the year #aggb4 ,the area engulfed was sixteen miles long and six broad4 ,the crater of ,kilauea1 in one of the ,sandwich ,islands1 was evidently formed in this way4 ,it is situated on the side of a mountain1 and consists of a chasm eight miles in circumference and a thousand feet in depth4 ,liquid lava can always be seen boiling in the small craters at the bottom2 and at times it rises so as to overflow them1 and fill the chasm to within four hundred feet of the top1 when lateral subterranean passages are opened1 by which it is discharged4 ,the same explanation--a depression of the central portion--may be given of the formation of the large craters in the ,canary and ,grecian islands4 ,it is also probable that ,lake ,avernus and others1 in ,italy1 and some in ,germany1 have had a similar origin4 ,the subsidence of ,papandayang is of importance as a historical fact2 and it is not at all unreasonable to suppose that larger chasms of great depth were also sudden subsidences of a similar character4 ,lake ,superior has a depth considerably greater than the elevation of its surface above the level of the sea4 ,the bottom of the ,dead ,sea is two thousand six hundred feet below the surface of the ,mediterranean4 ,and at one place in the ,atlantic ,ocean a sounding was attempted with more than six miles of line1 without reaching bottom4 ,these sunken areas1 however1 though of great extent1 occupy only an insignificant portion of the entire surface of the earth4 #f4 ,the ,elevation of ,continents4--,the causes of change of level which have been given will not explain those slow vertical movements which are now taking place in ,greenland and the north of ,europe1 or those by which the present continents have been elevated and the bed of the sea depressed4 ,any cause which will account for these movements must be one operating for long periods1 under large areas1 and with great uniformity4 ,the cause which fulfils all these conditions most satisfactorily is a variation of temperature in the mass of rock underlying the portion of the surface whose level is changing4 ,it has before been shown that the temperature increases as we descend below the surface2 but there is also reason to suppose that it undergoes great variations4 ,the volcanic grits interstratified with the silurian rocks of ,england show that at the silurian period volcanic fires were active below that portion of the surface4 ,when the early fossiliferous rocks of this country were deposited1 the ,alleghany ,mountains had not been elevated2 but before the tertiary period they had taken nearly their present form4 ,some portion of the intermediate period was therefore one of volcanic upheaval4 ,the trappean rocks are also evidence of intense volcanic action existing here4 ,france1 during the tertiary period1 was a highly volcanic country2 but all volcanic activity has now subsided4 ,the ,andes have been mostly elevated since the tertiary period1 and are still rising4 ,it is evident1 then1 that at different periods volcanic heat may vary from its highest to its least degree of activity1 below any portion of the earth's surface4 ,this variation of temperature must be followed by variation of volume of the earth's crust2 that is1 it must produce expansion or contraction4 ,experiments have been made1 under the direction of the ,united ,states government1 to determine the expansion of the several kinds of rock used in our public works4 ,it was found that granite expands nearly one two hundred thousandth of its length for every degree of increased temperature1 limestone somewhat more than that1 and sandstone about twice as much4 ,taking the expansion of the granite as the basis of calculation1 and supposing the crust for a hundred miles in thickness to be undergoing change of temperature1 there would be a resulting difference of level exceeding two and a half feet for each degree of change in temperature1 or more than two thousand five hundred feet for a change of one thousand degrees4 ,this calculation is made upon the supposition that the law of expansion is the same for all temperatures1 and that no new conditions are introduced at high temperatures by the presence of aqueous particles4 ,we know1 however1 that solids expand more rapidly at high temperatures than at low1 and the elasticity of aqueous vapor at high temperatures must increase the rate of expansion of the rock through which it is diffused4 ,although we are not able to introduce1 numerically1 the effect of these two circumstances1 yet it is obvious that they must be considerable4 ,the mean elevation of land above the level of the sea is about nine hundred feet1 the mountain masses above that level not being included2 and the estimated mean depth of the ocean1 not including its chasms1 does not exceed two thousand six hundred feet4 ,the total elevation of the continental masses1 for which it is necessary to account1 does not therefore exceed three thousand five hundred feet4 ,this amount of vertical movement may evidently be produced by the expansion and contraction resulting from changes of temperature4 ,these changes of level must1 however1 be very gradual4 ,any diminution of temperature must result from the transfer of heat to the surface2 and the conducting power of rocks is very imperfect4 ,the lava in a crater is often so cooled on the surface that it can be walked on1 while but a few feet below it is still liquid4 ,lava currents continue in gradual motion long after the surface is nearly cold4 ,this was the case with one of the currents from tna for more than nine months after its eruption1 and with another for ten years4 ,humboldt visited ,jorullo forty years after it was thrown up1 when the lava around the mountain was still in a heated state1 the temperature in the fissures being on the decrease from year to year2 but twenty years after its ejection the heat was still sufficient to light a cigar at the depth of a few inches4 ,if so long a period is insufficient to solidify a comparatively small quantity of melted rock when the circumstances for cooling are most favorable1 we may well suppose that centuries would be required to abstract sufficient heat from the earth's crust to produce any material change in the areas of continents4 ,if this account of the elevation and subsidence of continents is correct1 it would seem that they ought to be constantly undergoing change of level4 ,and their apparent stability may be regarded as an objection to it4 ,if in any place there is absolutely no vertical movement1 then those conditions must exist in which1 for the time being1 there is no change of temperature4 ,but it is doubtful whether there ever is absolute stability of any portion of the surface for long periods of time4 ,of the minor vertical movements of the interior of continents1 there can1 from the nature of the case1 be no evidence whatever4 ,changes of level1 where they are known to be taking place1 are so slow1 that they are hardly perceptible in the period of a human life4 ,such changes had been going on for centuries in ,sweden before they were suspected4 ,as accurate observations have increased in number1 and historical records become available1 it is becoming known that a very large amount of the seaboard is undergoing change of level4 ,it becomes probable1 then1 that these extremely slow changes of level are constantly and everywhere taking place4 ,that portion of the crust of the earth constituting the present continents1 being further removed from the centre1 would part with its heat more rapidly1 and receive heat from the central mass more slowly1 than that portion which at present constitutes the bed of the sea4 ,the continents are therefore in a situation to undergo contraction and depression1 and the bed of the sea is most favorably situated for rising4 ,if the distribution of water through the mass has any influence in promoting its expansion1 then the bed of the sea would receive this supply most abundantly1 and the continents the least so4 ,we see1 then1 in nature1 those provisions for an alteration of level1 which1 from the character of the several rock formations1 we know to have taken place4 ,when any portion of the earth's surface is covered with the sea1 the conditions exist which will at length elevate it4 ,when it becomes dry land1 the conditions exist which will in time depress it below the level of the ocean4 ,hence1 those impressions in regard to the land1 as stable beyond the possibility of change1 we ought to abandon2 and those vertical movements1 which1 when proved1 we are accustomed to regard as extraordinary1 we shall1 at length1 consider as only particular instances of one of the most general laws of nature4 #g4 ,variations of ,climate4--,the only sources of heat by which climate can be affected are the sun and the heated interior of the earth4 ,if the former melted condition of the entire mass of the earth be assumed1 the temperature of the surface must have been increased1 by conduction of heat from within1 for long periods after the superficial stratum had become solid4 ,it is1 however1 susceptible of proof1 that the present climates are not sensibly affected by interior heat1 though at a little more than a mile below the surface the temperature is equal to that of boiling water4 ,at any time1 therefore1 after the waters had become condensed1 collected into oceans1 and become sufficiently cool to support the animal life of which the remains are now found1 it is not probable that the climate was1 to any considerable extent1 influenced by the heat conducted from the interior4 ,still1 there have been great changes of climate since those early organic forms existed2 and1 since we have no ground for supposing that the temperature of the sun's rays has suffered any reduction1 we have to inquire whether the means of retaining the heat from the sun could at any time have been different4 ,the relative position of land and water depends1 as we have seen1 upon igneous causes1 and has been very different at different times4 ,we shall find that climate must have been greatly modified by these changes2 for the land radiates and absorbs heat freely1 and water possesses this power in a very low degree4 ,let us suppose the zone comprised between the tropics to be occupied by land1 and the portions without these limits to be covered with water4 ,under these conditions1 the land1 having a nearly vertical sun the whole time1 would accumulate heat to a degree scarcely compatible with the existence of animal life4 ,this is sufficiently proved by the oppressive tropical climates of the present time1 influenced as they are by polar lands and contiguous seas4 ,under the same conditions1 the sea would be heated by contact with the land1 and the heat would be distributed by marine currents to the polar regions4 ,but the water thus distributed would not part with its heat1 because it has but little radiating power1 and nowhere comes in contact with polar land4 ,it follows1 then1 that both land and water would be subjected to a very high temperature4 ,but1 if we suppose the land confined to the polar regions1 and the sea to the equatorial1 the opposite results would follow4 ,the equatorial sea would absorb but a small proportion of the solar heat which would be thrown upon it4 ,the land would receive the sun's rays too obliquely to receive much elevation of temperature1 as the present polar climates show4 ,hence1 the temperature of the earth would differ but little from that of the planetary spaces1 which is fifty-eight degrees below zero1 a temperature too low to allow of any considerable development of organic life4 ,these are the conclusions to which we are led by considering the different powers of land and water to absorb and radiate heat1 and we shall find that the existing climates are in accordance with these conclusions4 ,america has a lower temperature than ,europe in the same latitudes4 ,it has also a smaller proportion of land in the equatorial regions1 and a greater proportion in the north polar regions4 ,the eastern continent is colder in ,asia than in ,europe in the same latitudes4 ,it has also less equatorial and more polar land4 ,the southern is colder than the northern hemisphere at equal distances from the equator4 ,there is also less land near the equator on the south side1 and probably as much land around the south as the north pole4 ,hence1 we see that there may have been such a relation of land and water as to account for all the variations of temperature which are known to have existed4 ,we cannot say that such actually has been the case4 ,we can tell1 with some degree of accuracy1 what portions of the present continents were land at the several geological periods2 but three-fourths of the surface of the earth is covered with water1 and of the condition of this portion during those periods we have no means even of conjecturing4 ,we can only say1 that1 by the operation of known causes1 the relative position of land and water may have been such as to produce the climates known to have existed at former periods of the history of the earth4 ,,index4 ,page ,a4 ,abundance of vegetable products of the coal period1 #ei ,accumulation of vegetable matter1 #aag ,actinolite1 #ae ,action of internal heat1 #abh ,action of waves1 #ajg in forming harbors1 #ajh ,advantages of geological changes1 #ia tna1 #bf1 #gc ,agate1 #ad ,age of rocks1 doubtful-- from change of lithological character1 #fa from distance1 #fa from disturbance1 #fa ,alternation of coarse and fine material1 #aae ,aluminium1 #ab ,amethyst1 #ad ,amygdaloidal structure1 #ag ,ancient volcanic rocks1 #bi ,andes1 granite veins in1 #be ,angle of inclination1 #ga ,anoplotherium1 #ee ,anticlinal axis1 #ga ,aqueous causes1 #ajc ,aqueo-glacial action1 #abj ,argillaceous schist1 #bj1 #ca ,arrangement of materials in the crust of the earth1 #ba ,artesian wells1 #ib ,asbestos1 #ae ,atmospheric causes1 #ie ,atolls1 #ha ,augite1 #ae ,auvergne1 volcanic district of1 #bh ,b4 ,basalt1 #ah ,bed of the sea-- sunken areas in the1 #adb why elevated1 #ade ,belemnites1 #eb ,breccia1 #ai ,brine springs-- in ,silurian rocks1 #ce in the carboniferous formation1 #dc in the new red sandstone1 #dg ,c4 ,calamite1 #dg ,calcium1 #ac ,cambrian system1 #cb ,carbon1 #aa ,carbonate of lime1 #ae ,carbonate of magnesia1 #ai ,carbonic acid a cause of disintegration of rocks1 #ie ,carboniferous formation1 #ci essential to national wealth1 #dc extent of1 #dg a prospective arrangement1 #dc faults in1 #da not always disturbed by faults1 #db ,carboniferous limestone1 #ci sometimes becomes a coal-bearing rock1 #db fossils of the1 #dj ,carnelian1 #ad ,cause of internal heat1 #abh ,cause of stratification1 #aad ,caverns1 #fi ,cephalaspis1 #ci ,cephalopoda1 #cf in olite1 #ej ,chalcedony1 #ad ,chalk1 #eb ,changes of climate1 #hh how produced1 #adf ,changes in the crust of the earth1 #fg of temperature a disintegrating agent1 #if at the surface1 #he ,chemical action1 #ig in solids1 #ii in crystallization1 #ig ,chlorine1 #ab ,chlorite1 #ae ,chlorite slate1 #cb ,classification of rocks1 #ba ,clay1 #ai ,clay slate1 #bj ,cleavage structure1 #fh1 #ih ,coal1 #af varieties of1 #db mode of quarrying1 #db origin of1 #aaf conversion of vegetable matter into1 #aag now forming1 #aah ,coal measures1 #aca fossils of the1 #dd ,coal plants1 tropical character of1 #hh ,coal and iron associated1 #dc ,clouded marble1 #cc ,columnar structure1 #ah1 #ii ,compact limestone1 #ai ,concretionary formations1 #ii ,conglomerate1 #ai of old red sandstone1 #ch ,connecticut valley-- one of denudation1 #hg trap of1 #cj ,continents-- mean elevation of1 #add total elevation of1 #add elevated gradually1 #add why depressed1 #ade ,contorted strata1 #gb ,coral formation1 #ha1 #ajb extent of1 #ajb ,coral reefs-- fringing1 #ha barrier1 #ha ,coral rag1 #di ,corals in silurian rocks1 #ce ,copper mines of ,lake ,superior1 #dg ,creation1 a progressive work1 #fb ,cretaceous formation1 #eb ,cretaceous formation1 fossils of1 #eb geographical range of1 #ec ,crinoidea in ,silurian rocks1 #cf ,crust of the earth1 #af expansion and contraction of1 #adc ,d4 ,delta deposits1 #aad ,denudation of igneous rocks1 #he ,denudation of sedimentary rocks1 #he ,denudation produced by earthquake waves1 #acf ,deposition of sediment1 #aac ,diluvium1 #bj ,dike1 #fi1 #acc ,divisional planes1 #fh1 #ih ,dolomite1 #ac1 #ai ,drift1 #bj extent of1 #ec connected with striated surface of the rocks1 #ed connected with subsidence1 #ed1 #abf ,e4 ,earth in a state of change1 #ig ,earthquakes1 #acj wave-like motion of1 #acf ,earthquake waves1 rocks shivered by1 #acg ,effect of atmospheric agencies1 #ie ,electrical discharges1 effect of1 #if ,elementary substances1 #aa ,elevation and subsidence1 #gc ,elevation and subsidence several times repeated1 #hb ,elevation of mountains1 #gc cause of1 #aci spasmodic1 #adj gradual1 #ge ,elevation of different mountains at different times1 #ge ,elevation of continents1 #gf cause of1 #adb ,elevation of ,north ,america1 #gf ,elevation of the coast of ,maine1 #gf ,elevation of ,europe1 #gg ,elevation of ,south ,america1 #gh ,encrinites1 #cf1 #ej ,f4 ,fault1 #da1 #fi ,felspar1 #ad ,filling up of lakes1 #gf ,fingal's cave1 #cj ,fissile structure1 origin of1 #fh ,flint1 #ad in chalk1 #eb1 #ii ,fluorine1 #ab ,folded axes1 #fa1 #gb ,formation of soils1 #hg ,fossils-- definition of1 #eg how preserved1 #eg mineralization of1 #eh use of1 #fj order in which animals appeared1 shown by1 #eh animal and vegetable1 created together1 #ei as a record of climate1 #hh1 #aja ,fossiliferous rocks1 #cb classification of1 #cb ,fractures1 #db1 #fh1 #acj opening downward1 #acc ,g4 ,garnet1 #af ,geological causes1 how far uniform1 #id ,geological causes1 slow operation of1 #ie ,geological investigations aided by displacement of strata1 #ib ,geological periods1 prolonged1 #fc shown by amount of strata1 #fc shown by duration of species1 #fd shown by amount of organic matter1 #fd shown by microscopic accumulations1 #fe ,geology and ,revelation1 #fe ,giant's ,causeway1 #cj ,glacial period1 #ij ,glacial theory1 #abd ,glaciers-- how formed1 #abj cause of motion1 #aba when they decrease1 #abb earthy matter on them1 #abb lateral moraines1 #abc surfaces grooved by1 #abc terminal moraines1 #abc ,gneiss1 #ah1 #cj ,gorge1 #fi ,graham ,island1 #aca ,granite1 #af varieties of1 #af thickness of1 #bc structure of1 #bc formation of1 #fg igneous origin of1 #ach ,granite veins1 #bd in granite1 #bd ,granite of different ages1 #be ,granitic axes of mountains1 #bd1 #adj ,greensand1 #ai1 #eb ,greenstone1 #ah1 #cj ,grooved surfaces of rock1 #ed1 #hg1 #abf ,gypsum1 #ae in new red sandstone1 #dg beds1 how produced1 #ii ,h4 ,hall1 ,sir ,james1 experiments1 #ace1 #aci ,heterocercal tails of fishes1 #dh ,homocercal tails1 #dh ,hornblende1 #ad ,hornblende slate1 #bj1 #cb ,hydrogen1 #aa ,hypersthene1 #ae ,hypersthene rock1 #ag1 #be ,i4 ,icebergs-- how formed1 #abd earthy materials in1 #abe motion of1 #abe size and number of1 #abe effect in distributing drift1 #abf grooving the surface1 #abf ,iceland spar1 #ai ,iceland1 volcanic eruption in1 #bf ,ichthyosaurus1 #ej ,igneous causes1 #abg ,iguanodon1 #ea ,inclined position of strata produced by upheaval1 #gj1 #adj ,increase of temperature below the surface1 #abg ,iron1 #ab ,j4 ,jasper1 #ad ,jorullo1 #aca ,k4 ,kilauea1 #bf1 #adb ,l4 ,lakes1 filling up of1 #gf1 #aac ,lava1 #ag1 #be1 #acg varieties of1 #be tertiary1 #bg elastic vapors contained in1 #acj1 #acb great quantity of modern1 #bf ,lead-bearing strata1 #ce1 #dj ,lepidodendron1 #df ,lias1 #ai1 #di ,limestone1 #ae1 #ai as a primary rock1 #be metalliferous1 #dj ,local changes of climate1 #ij ,m4 ,magnesian limestone1 #ai1 #dg ,magnesium1 #ac ,mammoth1 #ef ,man-- recently created1 #ei as an agent in producing geological changes1 #aja impressions of the feet of1 #ei skeleton of from ,guadaloupe1 #ei ,manganese1 #ab ,marine currents1 #ajh ,marine currents1 cause of1 #aji abrading power of1 #aaa ,marl1 #ai ,mastodon1 #ee ,megatherium1 #ee ,metamorphic changes1 #fg ,metamorphic rocks1 #cj amount of1 #fg origin of1 #acd order of superposition1 #ca upper limit variable1 #ac localities of1 #cb ,metallic ores1 #ib ,mica1 #ad slate1 #ah1 #ca ,millstone grit1 #dj fossils of1 #da becomes coal measures1 #db ,mineral-- definition of1 #ac ,mineral veins1 #fi formation of1 #ajj ,modern formation1 #eg why but little known1 #eg fossils1 #eg ,moisture of the atmosphere a disintegrating agent1 #if ,monte ,nuovo1 #bf ,mount ,loa1 eruption of1 #bf ,n4 ,neocomian system1 #eb ,new red sandstone1 #dg fossils of1 #dh ores of1 #dg geographical range of1 #di ,niagara ,falls1 how preserved1 #ajf ,nitrogen1 #aa ,nummulite rock1 #ed ,o4 ,oceanic mountains1 #ge ,ocean level1 nearly permanent1 #gd ,old red sandstone1 #ch fossils of1 #ci extent of1 #ci ,olite1 #ai ,olitic structure1 #di ,olite system1 #di calcareous1 #di fossils of1 #ej localities of1 #ea ,opal1 #ad ,organic causes1 #aja ,orthoceras1 #cf1 #dj ,outcrop1 #ga ,oxide of iron1 #af ,oxygen1 #aa ,p4 ,paleotherium1 #ee ,papandayang1 #ie1 #adb ,permian system1 #dg ,plesiosaurus1 #ea ,porphyritic structure1 #ag ,potassium1 #ab ,primary limestone1 #ai ,pterodactyle1 #ea ,pumice-stone1 #ag ,pyroxene1 #ae ,q4 ,quartz1 #ad rock1 #cb ,r4 ,raindrops1 impressions of1 #dh ,raised beaches1 #gf ,ravine1 #fi ,recent elevation in ,europe1 #gi ,recent formation1 #eg ,ripple marks1 #dh ,rivers-- beds of1 raised1 #aac continued into the sea1 #aab abrading action of1 #aje abrading action of promoted by foreign substances1 #ajf ,rock crystal1 #ad ,rock salt1 #af1 #aah ,rocks1 denned1 #af ,rose quartz1 #ad ,s4 ,saccharine limestone1 #ai1 #cb ,saliferous system1 #dg ,saline properties of the ocean1 how obtained1 #ajd ,salt beds-- where found1 #aah how formed1 #aai ,sandstone1 #ai ,schorl1 #af ,scori1 #ag1 #acc ,sediment-- amount of in rivers1 #ajg deposition of1 #aac sorted by rivers1 #aab ,selenite1 #af ,serpentine1 #ae a primary rock1 #be ,shale1 #bj ,siberia1 remains of elephants in1 #hi ,sigillaria1 #de ,silicium1 #ab ,sinking of wharves1 towns1 c41 #gi ,silurian system1 #cd tabular arrangement of1 #cd divisions of1 #ce fossils of1 #cf geographical range1 #ch ,slaty structure-- in the gold washings of ,chili1 #ih produced by electric currents1 #ih ,slope of mountains1 #gc ,soapstone1 #ae ,sodium1 #ac ,solidification of rocks1 #fh1 #aai ,soluble materials of rocks1 #ajc ,solution of mineral substances-- promoted by heat1 #ajd promoted by an alkali1 #ajd promoted by carbonic acid1 #aje ,sources of the sedimentary materials1 #ajc ,sources of the sediment of rivers1 #ig ,species-- disappearance of1 #fb causes of the disappearance of1 #fb ,springs1 #ib ,stability of continents only apparent1 #ade ,statuary marble1 #ai ,stigmaria1 #dd ,strata-- horizontal1 #gj1 #aae permeable and impermeable1 #ib irregular1 how produced1 #aae ,striated surfaces1 #hg ,submerged forests1 #gi ,subsidence of land1 #gi1 #ade ,subsidence of land in ,greenland1 #hb ,subsidence and elevation in the ,pacific1 #hj ,sulphate of lime1 #ae ,sulphur1 #ab ,sun-cracks1 #dh ,sunken areas1 #adb ,syenite1 #ag ,synclinal axes1 #gb ,t4 ,taconic system1 #cb ,talc1 #ae ,talcose slate1 #bj1 #cb ,temperature at great depths1 #abg ,temple of ,jupiter ,serapis1 #hc ,tertiary system1 #ec age1 how determined1 #ec fossils1 #ed divisions of1 #ec geographical range1 #ef ,tilestones of the old red sandstone1 #ch ,trachyte1 #ah ,tracks in new red sandstone1 #di ,transportation of sediment1 #aaa ,trappean rocks1 #ag localities of1 #bi ,tremolite1 #ae ,trias1 #dg ,trilobite1 #cg1 #dj ,v4 ,valley1 #fi of elevation1 #ga1 #ge of subsidence1 #gb ,valley of denudation1 #hg ,vein of segregation1 #fi ,verd-antique marble1 #ae ,volcanic rocks1 #ag1 #be of different ages1 #bf in what states ejected1 #be ,volcanic mountains1 dimensions1 #bf ,volcanic activity-- regions of1 #abi water essential to1 #acj ,volcanic cones-- formation of1 #aca lateral1 #acb ,volcanic cinders1 scori1 glass1 #acb ,volcanic action1 effects of1 #acc ,volcanic origin-- of trappean rocks1 #ach of granitic rocks1 #ach ,volcanoes-- number1 #bf linear arrangement of1 #aca near the sea1 #abi new1 #aca of the tertiary period1 long active1 #bh ,w4 ,watt on fusion of basalt1 #ajj ,waves1 action of1 #ajg ,wealden1 #di ,wind a geological agent1 #if ,z4 ,zechstein1 #dg ,,questions ,,to ,,elements ,,of ,,geology ,,questions4 ,,chapter ,i4 ,,section ,i4 ,how many elementary substances are known8 ,in what combinations is oxygen found8 ,what proportion of the earth's crust consists of it8 ,in what combinations does hydrogen occur8 ,nitrogen8 ,carbon8 ,sulphur8 ,chlorine8 ,fluorine8 ,iron8 ,manganese8 ,how does silicium occur8 ,aluminium8 ,potassium8 ,sodium8 ,calcium8 ,magnesium8 ,how are these elementary substances classified8 7,silicium1 or silicon1 has but a doubtful claim to be regarded as metallic47 ,,section ,,ii4 ,what is a simple mineral8 ,how many are known8 ,what are the physical properties of quartz8 ,how are the several varieties distinguished8 ,what are the physical properties of felspar8 ,mica8 ,hornblende8 ,how are its varieties distinguished8 ,augite8 ,hypersthene8 ,talc8 ,how are its varieties distinguished8 ,serpentine8 ,carbonate of lime8 ,gypsum8 ,its varieties8 ,what other minerals are mentioned8 ,,section ,,iii4 ,define the crust of the earth4 ,rocks4 ,what are the unstratified rocks8 ,what is the structure of granite8 ,how are the varieties distinguished8 ,what is the porphyritic structure8 ,describe hypersthene rock4 ,what are volcanic rocks8 ,lava8 ,scori8 ,pumice-stone8 ,how is the vesicular structure produced8 ,what are volcanic breccias8 ,volcanic grits8 ,what is the composition of the trappean rocks8 ,what is the amygdaloidal structure8 ,what are the three varieties of trappean rocks1 and how are they distinguished8 ,illustration3 ,fig4 #a4 ,name the stratified rocks4 ,describe gneiss4 ,mica slate4 ,sandstone4 ,conglomerate4 ,greensand4 ,describe the varieties of limestone4 ,what is dolomite8 ,of what does clay consist8 ,clay slate8 ,what modifications does clay slate present8 ,what is diluvium8 ,,chapter ,,ii4 ,,section ,i4 ,what is the primary division of rocks8 ,upon what principle are the unstratified rocks divided8 ,upon what principle are the stratified rocks divided8 ,why are the non-fossiliferous called metamorphic rocks8 ,name the four classes of rocks4 ,,section ,,ii4 ,what is the most abundant plutonic rock8 ,how is its thickness ascertained8 ,what is its amount8 ,where is it found8 ,what is its ordinary structure8 ,what peculiarity of structure facilitates the cleavage of granite8 ,illustration3 ,fig4 #b4 ,the granitic masses are generally deep below the surface2 in what other position does granite appear8 ,illustration3 ,fig4 #c4 ,illustration3 ,fig4 #d4 ,in what classes of rocks are granite veins found8 ,were they all produced at the same time8 ,how is this demonstrated8 ,what is the relative position of the older and newer granites8 ,what other plutonic rocks occur in considerable quantities8 ,,section ,,iii4 ,of what do volcanic rocks consist8 ,in what states are they ejected8 ,what are the principal varieties of lava1 and how are they distinguished8 ,why is the basaltic lava the last to be ejected8 ,how is the age of the volcanic rocks determined8 ,what are the three divisions of the volcanic rocks1 as dependent upon age8 ,what is the proportion of the volcanic to other rocks8 ,how many active volcanoes exist8 ,describe the eruptions of ,kilauea4 ,describe the eruption in ,iceland in #aghc4 ,what are the dimensions of ,mount tna1 and how has it been produced8 ,how are the tertiary lavas known to be such8 ,where have they been most studied8 ,what is the evidence that these rocks in ,france are volcanic8 ,have these lavas been produced within the historic period8 ,illustration3 ,fig4 #e4 ,were they produced at an early period in the earth's history8 ,give the evidence that their activity was long-continued4 ,illustration3 ,fig4 #f4 ,what is the form of the earlier volcanic rocks8 ,what circumstances distinguish the trappean from other volcanic rocks8 ,what are some of the prominent localities of the trappean rocks8 ,how do they occur in the islands west of ,scotland8 ,how in the valley of the ,connecticut river8 ,,section ,,iv4 ,what is the lowest metamorphic rock8 ,describe it4 ,how does mica slate differ from gneiss8 ,is it well distinguished from argillaceous slate8 ,what is the third rock in the metamorphic series8 ,why is it difficult to determine the upper limit of this series8 ,why do the principal rocks of this series occur in the order here given8 ,what other rocks may take the place of these principal rocks8 ,where do the metamorphic rocks occur8 ,what is their thickness and amount8 ,,section ,v4 ,how many systems of fossiliferous rocks are there1 and what are they8 ,what other system is provisionally introduced8 ,what is its position8 ,illustration3 ,fig4 #g4 ,describe it4 ,what materials of value are obtained from this system8 ,illustration3 ,fig4 #h4 ,what fossils does it contain8 ,in what localities is it found8 ,what explanation1 in reference to these rocks1 is given by those who deny that they constitute a distinct system8 ,illustration3 ,fig4 #i4 ,illustration3 ,fig4 #aj4 ,in what respects does the ,state of ,new ,york present the best facilities for studying the ,silurian system8 ,describe the ,champlain division4 ,illustration3 ,fig4 #aa4 ,the ,ontario division4 ,the ,helderberg division4 ,illustration3 ,fig4 #ab4 ,illustration3 ,fig4 #ac4 ,illustration3 ,fig4 #ad4 ,illustration3 ,fig4 #ae4 ,illustration3 ,fig4 #af4 ,describe the ,erie division4 ,what are the fossils of this system8 ,illustration3 ,fig4 #ag4 ,describe the ,crinoidea4 ,the ,cephalopoda1 and the two forms4 ,illustration3 ,fig4 #ah4 ,the ,trilobite4 ,what higher forms of animal life existed during the silurian period8 ,the geographical range of the system8 ,of what does the ,old ,red ,sandstone consist8 ,describe its three divisions4 ,what are its fossils8 ,illustration3 ,fig4 #ai4 ,describe the fishes of that period4 ,what was the peculiarity of the ,pterichthys8 ,of the ,cephalaspis8 ,where are the rocks of this system found8 ,how is the carboniferous system divided8 ,describe the carboniferous limestone4 ,what ores are found in it8 ,describe1 its fossils4 ,describe the millstone grit4 ,of what do the coal measures consist8 ,how does the ironstone occur8 ,describe the coal beds4 ,how is the continuity of the strata interrupted8 ,what variations from this general type occur in the formation8 ,illustration3 ,fig4 #bj4 ,illustration3 ,fig4 #ba4 ,describe the several varieties of coal4 ,how is the coal quarried8 ,illustration3 ,fig4 #bb4 ,what mineral springs occur in this formation8 ,to what uses is coal applied8 7,the coal was deposited thousands of years ago1 and has served no useful purpose1 that we know of1 till very recently4 ,its formation was planned and completed to meet a want which was not to be felt till the lapse of many ages4 ,it is a notable instance of the wisdom and forethought1 as well as of the benevolence1 of ,god47 ,in what does this prospective arrangement consist8 ,what are the character and position of the fossils of the coal measures8 ,illustration3 ,fig4 #bc4 ,illustration3 ,fig4 #bd4 ,illustration3 ,fig4 #be4 ,illustration3 ,fig4 #bf4 ,what are the four most abundant forms8 ,describe the ,stigmaria4 ,the ,sigillaria4 ,the ,lepidodendron4 ,the ,calamite4 ,where are the beds of coal found8 ,what is the fourth formation of rocks8 ,into what two portions is it divided8 ,of what does the ,permian portion consist8 ,the ,trias8 ,what minerals are found in this formation8 ,what springs8 ,illustration3 ,fig4 #bg4 ,illustration3 ,fig4 #bh4 ,illustration3 ,fig4 #bi4 ,what fossils8 ,how are the fishes of the earlier and later portions distinguished8 ,what peculiarity of the red sandstones is mentioned8 ,by what kinds of animals were the tracks1 which they contain1 made8 ,give localities of the new red sandstone4 ,what are the three divisions of the ,olitic system8 ,illustration3 ,fig4 #cj4 ,illustration3 ,fig4 #ca4 ,illustration3 ,fig4 #cb4 ,describe the ,lias4 ,the ,olite4 ,the ,wealden4 ,what are the general peculiarities of the system8 ,illustration3 ,fig4 #cc4 ,what are the fossil animals of the system8 ,by which class of fossil animals is the system characterized8 ,illustration3 ,fig4 #cd4 ,describe the ,ichthyosaurus4 ,the ,plesiosaurus4 ,pterodactyle4 ,the ,iguanodon4 ,where is the system developed8 ,what are the divisions of the ,cretaceous system8 ,how are the layers of chalk separated8 ,what is the geological position of the ,neocomian system1 and the greensand of this country8 ,what are the fossils of this system8 ,illustration3 ,fig4 #ce4 ,illustration3 ,fig4 #cf4 ,what the geographical range8 ,how are the tertiary deposits distinguished from the older formations8 ,upon what principle is the tertiary system divided8 ,what are these divisions called1 and what does each1 name signify8 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #ch4 ,illustration3 ,fig4 #ci4 ,illustration3 ,fig4 #dj4 ,illustration3 ,fig4 #da4 ,illustration3 ,fig4 #db4 ,illustration3 ,fig4 #dc4 ,in what portion of the tertiary period was the drift deposited ,what is the geographical range of the drift8 ,of what does it consist8 ,what is the latest tertiary deposit8 ,what are the fossils of the tertiary system8 ,describe the ,paleotherium4 ,the ,anoplotherium4 ,the ,megatherium4 ,the ,mastodon4 ,the ,mammoth4 ,what other animals belonged to this period8 ,where are the tertiary deposits found8 ,what formations are regarded as recent8 ,what formations of this class are accessible8 ,what others are in progress8 ,what are the fossils of this formation8 ,,section ,,vi4 ,what is a fossil8 ,in what ways are they preserved8 ,when is a fossil said to be mineralized8 ,describe the process of mineralization4 ,how is it proved that the removal of the organic matter and substitution of mineral particles are simultaneous8 ,were animals created before vegetables8 ,how is this shown8 ,at what period was the vegetable growth the greatest8 ,what forms of animal life were most abundant during the earlier periods8 ,what vertebrated animals belonged to these periods8 ,what advance is made in the new red sandstone period8 ,during what period do the mammalia first appear in abundance8 ,during what geological period was man created8 ,how are the footprints and skeletons of human beings hi solid rocks accounted for8 ,why are not fossils distributed uniformly through all the formations1 and through all the parts of each formation8 ,in what does the importance of fossils consist8 ,how are the fresh-water and marine formations distinguished8 ,what circumstances render it difficult to identify rocks of the same age in different localities8 ,how are formations identified8 ,was the work of creation one of short duration8 ,what was the last work of creation of which we have any geological evidence8 ,why may we presume that no more species will be created8 ,do all the animal and vegetable species which have been created still exist8 ,illustration3 ,fig4 #dd4 ,illustration3 ,fig4 #de4 ,illustration3 ,fig4 #df4 ,illustration3 ,fig4 #dg4 ,what causes are operating to destroy species8 ,,section ,,vii4 ,how long has it been since the creation of the earth8 ,how does the amount of stratified rock indicate the great antiquity of the earth8 ,how does the stratification show the same thing8 ,what is the proof that the principal strata were deposited before the creation of man1 and how does this fact bear upon the question of the antiquity of the earth8 ,give the argument drawn from the successive creations and disappearance of animal and vegetable species4 ,the argument drawn from the amount of organic matter in the stratified rocks4 ,the argument from slow accumulation4 ,what is the general conclusion from these facts8 ,why is this conclusion an important one8 ,what objection to it has been raised8 ,how is this objection answered8 ,what additional explanation is given8 ,,chapter ,,iii4 ,,section ,i4 ,what is the deepest geological change of which we have any knowledge8 ,what are the reasons for supposing that the lowest stratified rocks are undergoing fusion8 ,why are the lowest stratified rocks regarded as of mechanical origin8 ,what changes have they undergone8 ,,section ,,ii4 ,in what state were the stratified rocks deposited8 ,what change have they undergone in this respect8 ,how is the fissile structure produced8 ,how is the cleavage structure produced8 ,illustration3 ,fig4 #dh4 ,what is the third class of changes8 ,what do fractures at the surface become by the erosion of water8 ,how are caverns formed8 ,describe a vein of segregation4 ,a dike4 ,a mineral vein4 ,what is a fault8 ,were the inclined strata thus deposited8 ,how is it proved that they have taken the inclined position since they were deposited8 ,what is the direction of the dip8 ,what lines form the angle of inclination8 ,what is the outcrop of inclined strata8 ,the strike8 ,illustration3 ,fig4 #di4 ,illustration3 ,fig4 #ej4 ,illustration3 ,fig4 #ea4 ,illustration3 ,fig4 #eb4 ,illustration3 ,fig4 #ec4 ,describe an anticlinal axis4 ,a synclinal axis4 ,a valley of elevation4 ,a valley of subsidence4 ,illustration3 ,fig4 #ed4 ,illustration3 ,fig4 #ee4 ,illustration3 ,fig4 #ef4 ,when are strata unconformable8 ,what other disturbances have taken place in the strata8 ,when did these various disturbances take place8 ,how is it known that there has been no period of universal disturbance8 ,,section ,,iii4 ,how is it known that the mountains have been covered by the ocean8 ,illustration3 ,fig4 #eg4 ,illustration3 ,fig4 #eh4 ,were the granitic ridges thus covered8 ,has the level of the sea been1 to any considerable extent1 fluctuating8 ,how1 then1 have the rocks1 of which the mountain masses consist1 been covered by sea8 ,give the evidence that different mountains were elevated at different times4 ,has the process of upheaval been sudden or gradual8 ,how are the mountain valleys1 which have the direction of the mountain ranges1 been produced8 ,illustration3 ,fig4 #ei4 ,how is the existence of submarine mountains shown8 ,what is the movement by which continents are elevated8 ,state the evidence of the elevation of continents from the existence of elevated sea-beaches4 ,the evidence of the elevation of the coast of ,maine4 ,the evidence of elevation from the existence of lakes4 ,from the geographical range of the older strata4 ,the evidence of the recent elevation of ,south ,america4 ,of the rising of the north of ,europe4 ,state the proof of subsidence from the occurrence of submerged forests4 ,why are these changes but little observed8 ,illustration3 ,fig4 #fj4 ,what are the grounds for asserting that a change of level is taking place over a large area in the ,pacific and ,indian ,oceans8 ,illustration3 ,fig4 #fa4 ,illustration3 ,fig4 #fb4 ,illustration3 ,fig4 #fc4 ,illustration3 ,fig4 #fd4 ,what is the present state of the coast of ,greenland in this respect8 ,have the changes of level of the same place always been in the same direction8 ,give the evidence of elevation and depression in ,south ,america4 ,in ,italy4 ,illustration3 ,fig4 #fe4 ,what general conclusion may we draw in respect to the stability of the earth's surface8 ,to what extent can we ascertain the geography of past epochs8 ,what former relations of land and water are suggested as not improbable8 ,,section ,,iv4 ,how can we estimate the denudation which the igneous rocks have suffered8 ,how do faults indicate the denudation of the stratified rocks8 ,how do valleys indicate denudations8 ,describe the instance in ,scotland4 ,what is the evidence of denudation in the ,connecticut valley8 ,how are valleys produced8 ,illustration3 ,fig4 #ff4 ,what is the condition of the surface rock in the colder portions of the temperate zones8 ,illustration3 ,fig4 #fg4 ,illustration3 ,fig4 #fh4 ,with what is the surface rock generally covered8 ,how are soils formed8 ,how may soils be improved8 ,what is necessary to render soils fertile8 ,,section ,v4 ,what means have we of judging of the climate of former periods8 ,what was the climate of the coal period8 ,what animal fossils indicate a former warm climate8 ,what evidence that ,siberia once enjoyed a milder climate8 ,do similar indications appear in the southern hemisphere8 ,when has the climate of the earth been most uniform8 ,has the climate been growing gradually colder to the present time8 ,what is the evidence of a somewhat recent period of intense cold8 ,what recent local changes of climate are mentioned as having occurred8 ,,section ,,vi4 ,state the general advantages of geological changes4 ,by what changes have the coal-beds and other stratified rocks become accessible8 ,what advantage from these elevating forces in reference to the granitic rocks8 ,illustration3 ,fig4 #fi4 ,how do these changes affect our means of knowing the structure of the earth8 ,explain the origin of springs1 wells1 and artesian wells8 ,by what changes have the metallic ores become accessible8 ,in what light1 then1 are we to regard disturbances of geological structure8 ,,chapter ,,iv4 ,what is the object of the preceding chapters8 ,how can we arrive at a knowledge of the causes which have produced geological phenomena8 ,have geological causes always operated with the same intensity8 ,how are the means of forming correct geological theories increasing8 ,,section ,i4 ,how does oxygen become an agent in the disintegration of rocks8 ,how does carbonic acid operate in the disintegration of rocks8 ,what is the effect of moisture and rain8 ,what is the effect of variations of temperature8 ,what other atmospheric causes are mentioned8 ,how do these causes become important8 ,what are some of their effects8 ,,section ,,ii4 ,what are the changes which are to be referred to chemical agency8 ,mention some of the disturbances which give rise to chemical changes4 ,what are the principal effects of chemical action8 ,how is the cleavage structure accounted for8 ,illustration3 ,fig4 #gj4 ,illustration3 ,fig4 #ga4 ,mention instances which show that a cleavage may be established in a body in a solid state4 ,in it a crystalline arrangement of the particles of the mass8 ,what other divisional planes exist in rocks8 ,mention instances of concretionary formations4 ,why may not these concretions have been deposited as nodules8 ,how have these concretions been formed8 ,mention instances of segregation without the concretionary structure4 ,how was the segregation in these instances effected8 ,how is the columnar structure produced8 ,what is the origin of the mineral veins which are first mentioned8 ,how is it shown that other veins are not injected8 ,how were these veins formed8 ,what is the force by which these molecular changes have been effected8 ,,section ,,iii4 ,in what ways are geological changes produced by human agency8 ,of what are the organic remains1 in rocks1 the record8 ,what rocks contain organic materials in large quantity8 ,what is the most abundant organic product8 ,explain the mode of growth of corals4 ,give instances of extensive coral reefs4 ,what is the total amount of surface covered by the coral reefs8 ,,section ,,iv4 ,what degree of importance is attached to water as a geological agent8 ,what are the sources of the sediment which water deposits8 ,why is not the formation of the sedimentary rocks capable of being observed8 ,what is the first mode in which solid matter is taken up by water8 ,why are the waters of the ocean saline8 ,what effect has the temperature of water in the solution of silex8 ,what effect has an alkaline condition of water8 ,illustration3 ,fig4 #gb4 ,what rock is soluble in water charged with carbonic acid8 ,give an instance of limestone formation from such solutions4 ,how do rivers furnish sediment for the stratified rocks8 ,what determines the position of rapids in rivers8 ,what is the effect of waterfalls on the abrading action of rivers8 ,what is the peculiarity of rock at ,niagara which has prevented the fall from becoming a succession of rapids8 ,what other circumstance increases the abrading action of rivers8 ,what is the principal source of the sediment which is transported by rivers8 ,what is the annual amount of sediment furnished by the ,kennebec8 ,the ,merrimac8 ,the ,mississippi8 ,the ,ganges8 ,what is the general tendency of these abrading forces8 ,what is the effect of waves upon the coast1 when it consists of unsolidified materials8 ,describe their effect upon rocky coasts4 ,how is the encroachment upon such coasts shown8 ,illustration3 ,fig4 #gc4 ,what is the effect of waves of less power8 ,how are marine currents produced8 ,how are they increased by the evaporation of the torrid zone8 ,what are the most important marine currents8 ,which class of currents have the greater depth8 ,upon what does the power of deep currents depend8 ,how would the effect of these currents be increased by earthquakes8 ,where will the effects of these currents be greatest8 ,mention instances of these effects4 ,illustration3 ,fig4 #gd4 ,what must be the effect of such currents as the ,gulf-stream and ,mozambique channel8 ,mention1 generally1 the effects of these currents4 ,why does detrital matter remain suspended in the water of rivers8 ,how is the coarse and fine sediment separated8 ,why do river currents extend some distance into the sea8 ,what effect does this have in distributing the sediment which the rivers furnish8 ,upon what does the transporting power of marine currents depend8 ,when a river enters a lake1 why is its sediment deposited8 ,describe the effect4 ,when is sediment deposited in the beds of rivers8 ,describe the effects of this deposition4 ,where is most of the sediment deposited8 ,give the area of some delta deposits4 ,how do the deep-sea deposits now forming compare in extent with the earlier formations8 ,state the several circumstances by which a succession of deposits would be arranged in strata4 ,how are those differences produced upon which the separation into independent formations depends8 ,why are marine deposits nearly horizontal8 ,illustration3 ,fig4 #ge4 ,how are the irregular stratifications produced8 ,what peculiarity in the fossils will distinguish the lacustrine and marine deposits8 ,what peculiarity in reference to fossils will characterize the deep-sea deposits8 ,how is coal shown to be of vegetable origin8 ,why will the drift wood of the sea accumulate in particular localities1 and why will it sink8 ,why will it become buried beneath earthy matter8 ,how is it known that wood thus buried will1 at length1 become lignite8 ,how is lignite converted into mineral coal8 ,what is the proof of it8 ,have beds of coal been formed at other periods1 besides the carboniferous8 ,is it probable that coal-beds are now forming8 ,how did the flora of the carboniferous period differ from the existing flora8 ,illustration3 ,fig4 #gf4 ,are the alternations of the earthy and coal strata satisfactorily explained8 ,in what portions of the geological series are the deposits of salt found8 ,where is saline matter principally stored8 ,explain the conjectural formation of salt in the ,mediterranean ,sea4 ,what form do rocks take when deposited from a chemical solution8 ,how is sand or gravel solidified by the infiltration of mineral waters8 ,what is the effect of drying upon the solidification of rocks8 ,what is the effect of pressure8 ,what of heat8 ,,section ,v4 ,what is a glacier8 ,what is the extent of the glaciers of the ,alps8 ,what change does the mass of snow in the higher valleys of the glacier mountains undergo8 ,what is the source of supply to the glacier8 ,what is the cause of the motion of the glacier8 ,what is the usual annual motion8 ,why will the glacier melt but little at its under side8 ,where will the waste at the surface just equal the addition8 ,what circumstances vary the position of the terminus of the glacier8 ,illustration3 ,fig4 #gg4 ,what1 besides snow and ice1 enters into the composition of a glacier8 ,how are these materials supplied8 ,how is a lateral moraine formed8 ,what effect has the motion of the glacier on the rocky surface over which it passes8 ,what is the material by which this effect is produced8 ,how is the terminal moraine produced8 ,how may the moraines on the ,jura ,mountains be explained8 ,how has it been proposed to explain the striated surfaces of rocks found in the north of ,europe and ,america8 ,what is the objection to this extension of the glacier theory8 ,how does the ice accumulate along the coast in high latitudes to form icebergs8 ,why does it ultimately separate from the shore8 ,how does it become freighted with earthy matter8 ,in what direction do the icebergs float1 and why8 ,what are the dimensions of an iceberg1 estimated from the part that is visible8 ,illustration3 ,fig4 #gh4 ,where does the mass of ice increase1 and where diminish8 ,what will be the effect of its melting8 ,how is it supposed that icebergs may have striated the rocky surface8 ,what is probably the condition of the bed of the seas over which icebergs now float8 ,has the north of ,europe and ,america been so depressed1 during a period comparatively recent1 as to admit of this explanation of the drift phenomena8 ,,section ,,vi4 ,what is the condition of the interior of the earth with respect to heat8 ,how do the observations made in deep mines and wells prove this8 ,how far is the temperature influenced from the surface8 ,what is the general law of increment of temperature8 ,at what depth would most mineral substances be melted8 ,how is this conclusion confirmed8 ,what was probably the original state of the mass of the earth8 ,what other explanation may be given of this interior heat8 ,what is the elastic force upon which volcanic phenomena depend8 ,upon what does the fluidity of lava depend8 ,upon what does its porous structure1 when cooled1 depend8 ,why are volcanoes situated near the sea8 ,describe the principal lines of volcanic activity4 ,what are the forces tending to repress the elasticity of the mass below8 ,what will be the effect when the elastic is greater than the repressing force8 ,what produces the phenomena of the earthquake8 ,what is a volcano8 ,why are volcanoes generally arranged a linear direction8 ,under what circumstances will a new volcano be formed8 ,what instances are cited8 ,how is a volcanic cone formed8 ,why are lateral cones produced8 ,how are volcanic cinders formed8 ,scori8 ,volcanic glass8 ,illustration3 ,fig4 #gi4 ,give instances of fractures as results of volcanic action4 ,how are dikes formed8 ,illustration3 ,fig4 #hj4 ,by what agency have the changes in the metamorphic rocks been effected8 ,give the instance of metamorphic action from intrusive granite in ,norway4 ,what instance is given as occurring in ,new ,hampshire8 ,give the experiment by which it is shown that these changes will result from a high temperature4 ,illustration3 ,fig4 #ha4 ,what must be the condition of the lowest stratified rocks in regard to temperature8 ,why is not the stratification destroyed8 ,what changes are produced by this high temperature8 ,explain the connection of denudation and earthquake action4 ,what is the evidence that the surface of the earth is thrown into undulations during earthquakes8 ,what is the velocity of these undulations8 ,give the instance which occurred in ,chili4 ,to what parts of the earth are these undulations limited8 ,what condition of the surface may be regarded as resulting from this cause8 ,what is the class of rocks most obviously referable to volcanic agency8 ,how do the trap rocks differ from ordinary lavas8 ,why are they not vesicular8 ,why more crystalline8 ,why were cones never formed8 ,what is the proof that the granitic rocks have once been in a melted state8 ,why does not the mass of melted rock below the surface retain permanently its liquid form8 ,why does it1 on cooling1 become more crystalline than lava8 ,state the process by which mountains are formed4 ,by what law does the elevating force accumulate8 ,why1 then1 is the process of elevation spasmodic1 and not constant8 ,how is the inclined position of strata produced8 ,how are strata brought into a vertical position over large areas8 ,why do subsidences occasionally follow these movements of elevation8 ,mention instances4 ,illustration3 ,fig4 #hb4 ,what explanation is suggested of deep and extensive chasms8 ,what conditions must exist together1 in the force by which continents are produced8 ,what cause fulfils these conditions8 ,what is the proof that the temperature under given localities is variable8 ,what will be the result of these variations8 ,what is the law of expansion of rocks1 as obtained by experiment8 ,what amount of change of level may be thus accounted for8 ,what circumstances would probably increase this amount8 ,what amount of vertical movement must be accounted for8 ,why must these changes of level be very slow8 ,under what conditions would there be no change of level8 ,is it probable that these conditions exist to any great extent8 ,why1 then1 are not the changes of level observed8 ,why is the bed of the sea most likely to experience the change of elevation8 ,why are the continents most favorably situated to undergo depression8 ,what are the sources of heat upon which climate depends8 ,does the interior temperature sensibly affect the present climates8 ,what cause may be assigned for the changes of climate which are known to have taken place8 ,what are the relations of land by which the highest temperature would be produced8 ,how would this distribution of land affect the temperature of the waters of the ocean8 ,what would result if the opposite relations of land and water existed8 ,what confirmation of these conclusions is drawn from the existing climates of different parts of the earth8 ,is there any reason to suppose that the relations of land and water which would have produced a warmer climate in former times did not exist8