Chap. IX. GEOLOGICAL RECORD. 289 



remains is fragmentary in an extreme degree. For 

 instance, not a land shell is known belonging to 

 either of these vast periods, with one exception disco- 

 vered by Sir C. Lyell in the carboniferous strata of 

 North America. In regard to mammiferous remains, a 

 single glance at the historical table published in the 

 Supplement to Lyell's Manual, will bring home the 

 truth, how accidental and rare is their preservation, far 

 better than pages of detail. Nor is their rarity sur- 

 prising, when we remember how large a proportion of 

 the bones of 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 palaeozoic formations. 



But the imperfection in the geological record mainly 

 results 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. When we see the formations tabulated in written 

 works, or when we follow them in nature, it is 

 difficult to avoid believing that they are closely con- 

 secutive. But we know, for instance, from Sir K. 

 Murchison's great work on Kussia, 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 skilful geologist, if 

 his attention had been exclusively confined to these 

 large territories, would never have suspected that during 

 the periods which were blank and barren in his own 

 country, great piles of sediment, charged with new and 

 peculiar forms of life, had elsewhere been accumu- 

 lated. And if in each separate territory, hardly any 

 idea can be formed of the length of time which has 

 elapsed between the consecutive formations, we may infer 

 that this could nowhere be ascertained. The frequent 



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