12 The Life and Writings of Agassiz. 



the whole body. Finally, neither has jaws, properly so call- 

 ed. Now, the most perfect of our fishes, such, for example, 

 as the Salmon, are all, at one period of their life, at the same 

 point of development, but with them it is a transient state, a 

 stage of growth ; whilst in the others it is the permanent con- 

 dition. 



These views have a high philosophical bearing, particu- 

 larly in their application to other classes of the animal king- 

 dom. It is in accordance with them that Agassiz determined 

 the rank to be assigned to the various families of fishes, ac- 

 cording to their organisation. 



It is to Geology, nevertheless, that the greatest profit is 

 derived from these discoveries. In comparing together the 

 fishes found in various formations, Agassiz, from the first, 

 had also thrown new light on the relative age of these for- 

 mations. Thus, to cite but a single example, he was enabled 

 by the study of the fishes of the slate of Glaris, to demon- 

 strate that this deposit, which had previously been consider- 

 ed as belonging to the most ancient sedimentary rocks, the 

 greywacke, is much more recent, and forms a part of the cre- 

 taceous group. Another and more general result of his la- 

 bours was the discovery, that not only are all the fossil spe- 

 cies diff^erent from those now living, but also, that from one 

 formation to another, the species are equally distinct ; and 

 this diversity, according to him, is not confined to the larger 

 formations, but exists equally between the various stages of 

 the same formation. Thus, he recognises no species as com- 

 mon to the lias and the upper Jura limestone ', to the upper 

 and lower cretaceous deposits ; to the ancient and recent 

 strata of the tertiary formations, &c. The necessary deduc- 

 tion is, that the whole creation has been renewed at different 

 epochs, by a direct intervention of the Creator. Agassiz, 

 however, did not stop here, but pushed his conclusions still 

 farther. From the fact that certain basins, like certain 

 regions of the earth's surface, are inhabited by species pecu- 

 liar to them, not found elsewhere in deposits of the same age, 

 he inferred that each creation was local, that is to say, that 

 species were created in the localities they inhabit, and that 

 to each was assigned a limit, which it does not pass so long 



