358 M. L, Agassiz on the Primitive Diversity and 



carboniferous deposit to the present day ; that is to say, ever 

 since terrestrial vegetation has had an extensive development. 

 The discoveries by Hugh Miller of true trees in the old red 

 sandstone will justify the prophecy that insects will be found, 

 some day or other, even among palseozoic rocks older than the 

 coal period. 



But what of the Vertebrata ? Is there not evidence that, at 

 the present day, they are more diversified and more numerous ? 

 Here, again, I answer decidedly. No ; granting only that there 

 are periods during which the higher classes of these types did 

 not exist, and that therefore, as a type, the Vertebrata of the 

 present day are more diversified; but the individual classes, 

 from the time of their appearance, have been as numerous and 

 even as various in each former period as they are at present. 



Let us apply to these the same measure which we have applied 

 to the Radiata, MoUusca and Articulata, to justify this assertion, 

 which seems so completely at variance with our knowledge of 

 fossil Vertebrata. Fishes occur, as is well known, in all geolo- 

 gical formations. But should we compare the fossil fishes of 

 each geological period, as they are known from a few localities, 

 with the whole number of fishes which exist all over the world 

 in our day ? It would be as unphilosophical as it would be in- 

 consistent with our knowledge of the geographical distribution 

 of animals. Like all other living beings, fishes are located 

 within definite boundaries, and it will be but fair to compare 

 the fossil species of a given locality with the special ichthyolo- 

 gical faunse which occur in difi'erent oceans, or in different fresh- 

 water basins. Now with this rule we may institute a comparison 

 of the fossil fishes with the living ones, with reference to their 

 number as well as to their variety. 



The number of species of fossil fishes known at present from 

 the tertiary deposits, in a single spot, upon the Island of Sheppey, 

 is greater than the number of fishes which have been collected 

 around the coast of any of the islands of the Pacific Ocean, as 

 far as we know the local ichthyological faunse of those regions ; 

 it is as great nearly as the whole number of fishes known from 

 the shores of Great Britain. The same may be said of the fishes 

 of Monte Bolca, or of Mount Lebanon, or of those of the white 

 chalk of England, or of those of Solenhofen, or of those of the 

 lias of Lyme Regis ; and if we pass to older deposits, to the old 

 red sandstone even, — thanks to Mr. Miller, and to the investiga- 

 tions of other British and Russian geologists, — do we not know 

 from that old formation as many fishes as from any of the more 

 recent ones, or from any circumscribed marine basin ? and is not 

 the variety which occurs among them at each period as great, 

 though of a difi'erent character in each, as the variety which 



