PALMONTOLOGICAL 00LLEGTI0N8. 331 



tertiary mammals have been discovered either in caves or in 

 lacustrine deposits; and that not a cave or true lacustrine 

 bed is known belonging to the age of our secondary or 

 palffiozoic formations. 



But the imperfection in the geological record largely re- 

 sults from another and more important cause than any of 

 the foregoing; namely, from the several formations being 

 separated from each other by wide intervals of time. This 

 doctrine has been emphatically admitted by many geologists 

 and palseontologists, who, like E. Forbes, entirely disbe- 

 lieve in the change of species. "When we see the forma- 

 tions tabulated in written works, or when we follow them 

 in nature, it is difficult to avoid believing that they are 

 closely consecutive. , But we know, for instance, from Sir 

 R. Murchison's great work on Russia, what wide gaps there 

 are in that country between the superimposed formations; 

 so it is in North America, and in many other parts of the 

 world. The most skillful geologist, if his attention had 

 been confined exclusively to these large territories, would 

 never have suspected that during the periods which were 

 blank and barren in his own country, great piles of sedi- 

 ment, charged with new and peculiar forms of life, had 

 elsewhere been accumulated. And if, in every separate 

 territory, hardly any idea can be formed of the length of 

 time which has elapsed between the consecutive forma- 

 tions, we may infer that this could nowhere be ascertained. 

 The frequent and great changes in the mineralogical com- 

 position of consecutive formations, generally implying 

 great changes in the geography of the surrounding lands, 

 whence the sediment was derived, accord with the belief of 

 vast intervals of time having elapsed between each for- 

 mation. 



We can, I think, see why the geological formations 

 of each region are almost invariable intermittent; that is, 

 have not followed each other in close sequence. Scarcely 

 any fact struck me more when examining many hundred 

 miles of the South American coasts, which have been up- 

 raised several hundred feet within the recent period, than 

 the absence of any recent deposits sufficiently extensive to 

 last for even a short geological period. Along the whole 

 west coast, which is inhabited by a peculiar marine fauna, 

 tertiary beds are so poorly developed that no record of sev- 



