442 Mr. De la Beclie's Sketch of a Classification 



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 I'ock 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, secondai'y, 

 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, 

 during each of which rocks of a peculiar character, distinct 

 from each other, were formed, and that there was a trans- 

 ition or passage only between the first and second of these. 

 I appeal to those who have examined rocks in the field, and 

 not merely in cabinets and museums, whether or not the stu- 

 dent would entertain correct opinions. These divisions may 

 be said to have been made in the infancy of the science, and 

 doubtless contributed much to its present comparatively ad- 

 vanced state ; but it should always be recollected that they were 

 formed from limited observations, and were connected with 

 particular theories, which recent and more accurate observa- 

 tions have shown to be any thing but correct. If it shall be 

 proved that there is an occasional passage between the old 

 tertiary and secondary classes, there would appear to be more 

 or less transition throughout the whole series of the stratified 

 rocks, showing that the term transition, at least, is incorrect. 

 A great mass of evidence is, indeed, in favour of a break at 



the 



