FOSSILS ARE ONLY THE HARD PARTS. 27 



Asia which have been minutely investigated, — the Cape 

 districts and the Himalaya mountains. A series of entirely 

 new and very peculiar animal forms have become known to 

 us from the rocks of these localities. But we must bear in 

 mind that the vast bottom of the existing oceans is at the 

 present time quite inaccessible to palseontological investiga- 

 tions, and that the gi-eater part of the petrifactions which 

 have lain there from primjeval times wiU either never be 

 known to us, or at best only after the course of many 

 thousands of years, when the present bottom of the ocean 

 shall have become accessible by gradual elevation. If we 

 call to mind the fact that three-fifths of the whole surface 

 of the earth consists of water, and only two-fifths of land, 

 it becomes plain that on this account the palseontological 

 record must always present an immense gap. 



But, in addition to these, there exists another series of 

 difficulties in the way of palaeontology which arises from 

 the nature of the organisms themselves. In the first place, 

 as a rule only the hard and solid parts of organisms can fall 

 to the bottom of the sea or of fresh waters, and be there 

 enclosed in the mud and petrified. Hence it is only 

 the bones and teeth of vertebrate animals, the calcareous 

 shells of moUuscs, the chitinous skeletons of articulated 

 animals, the calcareous skeletons of star-fishes and corals, 

 and the woody and solid parts of plants, that are capable 

 of being petrified. But soft and delicate parts, which 

 constitute by far the greater portion of the bodies of most 

 organisms, are very rarely deposited in the mud under cir- 

 cumstances favourable to their becoming petrified, or dis- 

 tinctly impressing their external form upon the hardening 

 mud. Now, it must be borne in mind that large classes of 



