of European Rocks. 151. 



influence, as it now exists, would be inadequate; we must 

 therefore have recource to internal heat to produce the effect 

 required. In the present varied temperature of the earth's 

 surface, if we imagine a rock to he formed which should 

 envelop every animal and plant now existing, the fossil con- 

 tents of one district would differ from the fossil contents of 

 another ; if we except man, whose bones would more or less 

 become the characteristic fossils of those portions of the rock 

 which might overlie the present dry land. The rock sup- 

 posed to be now formed would present a striking contrast with 

 the old fossiliferous, and we should have two very distinct 

 accumulations of organic remains. The question arising on 

 such phaenomena would be, Has so great a change of organic 

 character been effected gradually or suddenly ? To suppose 

 it sudden will not agree with the phaenomena presented to us, 

 even by the now known European rocks ; and if it be con- 

 sidered gradual, we cannot expect that rocks should every 

 where contain the same organic remains, even in those that 

 have been commonly called secondary : consequently the 

 organic remains considered characteristic of any particular 

 formation in one part of the world, may not be found at all in 

 an equivalent formation in another. 



Upon the theory that the world cooled in such a manner 

 that solar heat, as now existing, gradually acquired its in- 

 fluence, the warm climate vegetation would gradually be re- 

 strained within narrower limits, until it became circumscribed 

 as it now is ; consequently all rocks formed within the tropics 

 would probably contain warm climate plants, while these 

 would gradually cease on the N. and S.; so that it would be 

 by no means safe to deduce the kind of Flora that should be 

 found in any given rock in the tropics from the fossil plants 

 discovered in an equivalent rock in Europe. If vegetable life 

 might under such circumstances so vary, there seems no good 

 reason why animal life might not equally differ. To what ex- 

 tent the mass of organic fossils found in any particular Euro- 

 pean formation or group of formations may exist in equivalent 

 rocks (of Africa or America for instance), remains to be seen. 

 In the present state of our knowledge, it is only safe to state 

 that certain remains have been discovered in a given rock, 

 not that they are absent from it. 



The old divisions into primitive, transition, secondary, 

 and tertiary, are now admitted by many persons to be founded 

 on an erroneous view of nature ; yet such is the force of 

 habit, that many geologists, aware of the fallacy of these di- 

 visions, still continue to use the terms, and we hear nearly 

 as much as ever of transition rocks. Would it not be ima- 

 gined by a person first directing his attention to the study 

 of geology, that there were three great marked periods, 



