ORIGINATION OF LIVING BEINGS. 69 



creatures with which organic life began upon the 

 earth. And if we did so, and if such forms of organic 

 life were preservable, we should have what I would call 

 historical evidence of the mode in which organic life 

 began upon this planet. Many persons will tell you, 

 and indeed you will find it stated in many works on 

 geology, that this has been done, and that we really 

 possess such a record ; there are some who imagine 

 that the earliest forms of life of which we have as vet 

 discovered any record, are in truth the forms in which 

 animal life began upon the globe. The grounds on 

 which they base that supposition are these : — That if 

 you go through the enormous thickness of the earth's 

 crust and get down to the older rocks, the higher 

 vertebrate animals — the quadrupeds, birds, and fishes — 

 cease to be found ; beneath them you find only the in- 

 vertebrate animals ; and in the deepest and lowest rocks 

 those remains become scantier and scantier, not in any 

 very gradual progression, however, until, at length, in 

 what are supposed to be the oldest rocks, the animal 

 remains which are found are almost always confined to 

 four forms, — Oldhamia, whose precise nature is not 

 known, whether plant or animal ; Lingula, a kind of 

 mollusc; Trilobites, a crustacean animal, having the 

 same essential plan of construction, though differing in 

 many details from a lobster or crab ; and Hymenocaris , 

 which is also a crustacean. So that you have all the 

 Fauna reduced, at this period, to four forms : one a 

 kind of animal or plant that we know nothing about, 

 and three undoubted animals — two crustaceans and 

 one mollusc. 



