86 



GENERAL PHYSICAL GEOGRAPHY. 



depths ; and from the strange fragments which 

 I have found included in streams of lava in dif- 

 ferent quarters of the globe, I also hold it as 

 more than probable that a primogenial granitic 

 rock is the foundation of the great systems of 

 stratification which are filled with such variety 

 of organic remains(^°*). If basalts, containing 

 ohvine, first make their appearance in the cre- 

 taceous period, and trachytes show themselves 

 still later, the eruptions of granite, on the con- 

 trary, belong (as metamorphic productions also 

 assure us) to the epochs of the oldest sedi- 

 mentary strata of the transition series. Where 

 knowledge cannot take its rise from the imme- 

 diate scrutiny of the senses, it is fairly allow- 

 able, even on grounds of pure induction, as also 

 after a careful comparison of facts, to advance 

 a conjecture which restores to the olden gran- 

 ite a portion of its threatened rights, and its 

 distinction of primordiality. 



The late advances of geology, the extended 

 knowledge of the geological epochs, which are 

 characterized by the mineralogical diversity of 

 their rocks or mineral masses, by the peculiar- 

 ities and succession of the organic remains 

 which they contain, by the position, the erec- 

 tion or the undisturbed horizontal lie of the 

 strata, all these considerations lead us, follow- 

 ing the intimate causal connection of phenom- 

 ena, to the division, in respect of space, of the 

 solid and the fluid, of the continents and the 

 seas which constitute the surface of our planet. 

 And here we indicate a point of union between 

 that which is historical in geology with refer- 

 ence to the earth — cosmographical geology, and 

 geographical geology, or the general considera- 

 tion of the form and partition of continents. 

 The limitation of the Solid by the Fluid, and 

 the relations in respect of area between the one 

 and the other, have been very different at dif- 

 ferent times in the long succession of geologi- 

 cal epochs, according as the sedimentary car- 

 boniferous strata were deposited horizontally 

 on the upright strata of mountain lime- and old 

 red sand stone ; as lias and oolite were laid on 

 banks of kuper and muschelkalk ; and as chalk 

 was accumulated on the acclivities of the green 

 sand and Jura limestone. If, with M. Elie de 

 Beaumont, we designate the waters under 

 which the Jura limestone and the chalk were 

 precipitated in the shape of mud or slime, as 

 the Jurassic and cretaceous seas, then will the 

 contour of the two formations just mentioned 

 give us the boundary for two epochs, between 

 the ocean still engaged in forming rocks, and 

 the land already laid dry. The happy idea has 

 even been conceived of forming maps of these 

 physical elements of primeval geography ; and 

 these maps are perhaps more accurate than 

 those which have been composed in illustration 

 of the wanderings of To and the Homeric narra- 

 tives. The latter give graphic representations 

 of opinions and mythical images ; the former ex- 

 hibit facts in the positive science of formation. 



The result of investigations into the extent 

 of exposed area, or dry land, is this : that in 

 the earliest times, in the Silurian or Devonian 

 transition epochs, as also in the first floetz pe- 

 riod, throughout its tripartite division, the dry 

 land, the surface occupied by land plants, was 

 limited to separate islands ; that these islands 



united at later epochs, and inclosed numerons 

 inland lakes by the sides of deeply-indented 

 bays of the sea ; that finally, when the mount- 

 ain chains of the Pyrenees and Apennines and 

 Carpathians arose — towards the time of the 

 older tertiary strata, therefore — extensive con- 

 tinents, having almost the dimensions of those 

 of th^^esent day, had appeared. In the times 

 of jJ^littirian world, as well as in the epoch 

 of ^^^Hhest luxuriance of the Cycadeae and 

 gigaBBKaurians, the quantity of dry land from 

 pole to pole might very possibly have been 

 even less than it is in the Pacific and Indian 

 Oceans at the present time. How this prepon- 

 derating mass of water, in common with other 

 causes, conduced to elevation of temperature, 

 and to greater equality- of climate, will be the 

 subject of consideration by and by. Here it 

 iqust only be farther remarked, in considering 

 the gradual augmentation (agglutination) of the 

 uplifted dry land, that shortly before the revo- 

 lutions, which, after shorter or longer pauses 

 in the diluvial period, occasioned the sudden 

 extinction of so many gigantic vertebrate ani- 

 mals, portions of the present continental mass- 

 es were still completely separate from one an- 

 other. In South America and the Australasian 

 lands, there is a great prevailing resemblance 

 between the existing animals and those that 

 have become extinct. In New Holland, the 

 fossil remains of kangaroos have been discov- 

 ered, and in New Zealand the semifossil bones 

 of a gigantic struthious bird, Owen's Dinornis, 

 closely allied to the existing Apterix, but hav- 

 ing little affinity to the so lately extinguished 

 Dronte or Dodo of the island of Rodriguez. 



The outline of former continents was perhaps 

 indebted in principal measure for its elevation 

 above the surrounding sea-level to the eruption 

 of quartzose porphyry, an event which so pow- 

 erfully shook the first great vegetable covering 

 of the dry land, from which were derived the 

 materials of the coal measures. What we call 

 plains or flats (in continents), are no more than 

 the broad backs of hills and mountains whose 

 feet are at the bottom of the sea. Each plain, 

 in its submarine relations, is, in fact, a lofty 

 plateau or table-land, whose inequalities have 

 been concealed by new sedimentary deposi- 

 tions in horizontal beds, as well as by alluviums 

 spread over its surface by floods. 



Among the general considerations which be- 

 long to a Picture of Nature, the foremost place 

 must be given to the quantity of terra fir ma 

 projecting, uplifting itself above the level of the 

 sea ; such a determination of continental areas 

 includes the consideration of their individual 

 forms in point of horizontal extension (seg- 

 mentary relations), and of perpendicular eleva- 

 tion (the hypsometrical relations of mountain 

 chains). Our planet has two coverings or en- 

 velopes : one general, the Atmosphere, as elastic 

 fluid, and one particular, only locally distributed, 

 bounding the Solid, and thereby givmg it its 

 figure, the Sea. These two coverings, the air 

 and the ocean, form a natural whole which 

 gives the surface of the earth its climate, di- 

 verse according to 'the relative extent of the 

 sea and of the land, of the division and geo- 

 graphical position of the land, and of the direc- 

 tion and elevation of its mountain chains. 



