146 - CLUES AND SUGGESTIONS CHAP. 



great strength as to numbers, and in 

 great perfection as regards organisation. 

 The usual way of evading this great 

 difficulty in the facts of Geology is to 

 plead what is called the imperfection of 

 the Record. But this plea will not avail 

 us here. There are some tracts of time 

 respecting which our records are almost 

 as complete as we could desire. In the 

 Jurassic rocks we have a continuous and 

 undisturbed series of long and tranquil 

 deposits containing a complete record 

 of all the new forms of life which were 

 introduced during these ages of oceanic 

 life. And those ages were, as a fact, 

 long enough to see not only a thick 

 (1300 feet) mass of deposit, but the firs't 

 appearance of hundreds of new species. 

 These are all as definite and distinct from 

 each other as existing species. No less 

 than 1850 new species have been counted 

 all of them suddenly born all of them 



