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RELICS OK rUIMKVAL LIFE 



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deeply burled bcnc.ith later rocks, while the parts 

 exposed are precisely those which have by their 

 crumpling and pressure, and the influence of internal 

 heat, become most hardened and altered, and have 

 therefore best resisted denudation. We need not 

 therefore be astonished if any organic remains ori- 

 ginally present in imch rocks should have perished, 

 or should have been subjected to such changes of 

 composition and form as to have altogether lost 

 their original characters. The searcher for fossils 

 in such rocks has to expect that these can have 

 been preserved only under very rare and excep- 

 tional circumstances. We have now to consider 

 what these circumstances are, and for simplicity 

 may suppose that we are endeavouring to discover 

 in a crystalline limestone the remains of animals 

 having a skeleton of limestone, as is the case with 

 most shell-fishes and corals, and with many Protozoa 

 and marine worms. In regard to these, we have to 

 consider what may happen to them when Ihey are 

 imbedded in calcareous marl or ooze, or the limestone 

 which results from the hardening of such materials ; 

 and we have to bear in uvnd that such organisms 

 usually consist of hard, stony walls or partitions, en- 

 closing cavities originally filled with the soft parts 







