11G 



UNIFORMITY OF AQUEOUS CAUSES. 



[Ch. VI. 



been sufficient time since their origin for the development of 

 a great series of elevatory movements. 



In regard, however, to one of the most important character- 

 istics of sedimentary rocks, their organic remains, many 

 naturalists of high authority have maintained that the same 

 species of fossils are more widely distributed through forma- 

 tions of high antiquity than in those of more modern date 

 and that distinct zoological and botanical provinces, as they 

 are called, which form so striking a feature in the livino* 

 creation, were not established at remote eras. Thus the plants 

 of the Goal, the shells, and trilobites of the Silurian rocks 

 and the ammonites of the Oolite, have been supposed to have 

 a wider geographical range than any living species of plants, 



s 



crustaceans, or mollusks. This opinion seems in certain case 

 to be well founded, especially in relation to the plants of the 

 Carboniferous epoch, owing partly to greater uniformity of 

 climate, and partly, as Professor Heer has suggested, to the 

 fact that almost all the plants — including even large trees 

 of that period, were cryptogamous : so that their minute 

 spores might be carried by the wind for indefinite distances, 

 as are now the spores of ferns, mosses, and lichens. But a 

 recent comparison of the fossils of North American rocks with 

 those of corresponding ages in the European series, has proved 

 that the terrestrial vegetation of the Carboniferous epoch is 

 an exception to the general rule, and that the fauna and flora 

 of the earth at successive periods, from the oldest Silurian to 

 the newest Tertiary, was as diversified as now. The shells, 

 corals, and other classes of organic remains demonstrate the 

 fact that the earth might then have been divided into separate 

 zoological provinces, in a manner analogous to that observed 

 in the geographical distribution of species now living. 





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