M. Agassiz on Fossil Fishes. 841 



genu8 to another, and from one family to another, likewise re- 

 appear in those details. It is thus that the Sauro'ids, which 

 of all fishes approach nearest to Reptiles, have teeth of a 

 structure very similar to that of the Ichthyosauri, while the 

 Sharks, which occupy a lower degree in the scale, shew quite 

 a different structure. 



3. Importance of Fossil Fishes in a geological point of view. 

 It is by their geological importance that M. Agassiz*s B^e- 

 searches on Fossil Fishes are particularly destined to create a 

 sensation. Even in the earlier parts of the work, the author, 

 by comparing the fishes of the different formations, found an 

 opportunity of throwing new light on the relative age of many 

 of these formations. He was thus led (to mention only a single 

 example), by the study of the fishes enclosed in the slates of 

 Glaris, to demonstrate that this deposit, previously regarded 

 as belonging to the most ancient sedimentary formation, the 

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

 ceous formation. Another more general result of M. Agassiz's 

 work is, that not only all the fossil species are different from 

 those that live in our days, but that they are equally distinct 

 as we proceed from one formation to another. Besides this, 

 the author does not only limit these differences to the great 

 formations ; he establishes them also in the diverse stages of 

 the same formation. It is thus that he does not find identical 

 species in the lias and the upper Jura, in the inferior and su- 

 perior deposits of the chalk, in the ancient and recent por- 

 tion of the Tertiary class, &c. Now, the natural consequence 

 of these differences is, that the entire creation has been re- 

 newed at these different epochs by a direct intervention of the 

 Creator. Such a conclusion will perhaps seem rash ; but it 

 appears that observation tends to confirm it more and more ; at 

 least M. D'Orbigny arrives at nearly the same results by the 

 study of the testaceous animals. 



Along with these differences, so constant and so regular, the 

 author likewise discovers a genetic connection between the type 

 of fishes and that of the other classes of the vertebrata, when 

 their development is considered throughout the different geo- 

 logical epochs. The considerations which he attaches to this 



