

230 Parallelism of the Palaeozoic Deposits 



general form, and even others more remotely allied. We now 

 have Leptcena, Chonetes and Productus, while the genus Or this 

 includes other forms previously referred to Productus. Still 

 another genus of the Leptacnidce may be constituted, and we 

 shall have a more natural subdivision than at present, each one 

 possessing characters of important and peculiar value. 



While M. de Verneuil recognizes and clearly establishes the 

 genus Chonetes, we are surprised that he should unite all the 

 Terebratuloid forms in the genus Terebratula, when there is 

 ample room for subdivision. We believe, however, that we un- 

 derstand the motives of M. de Verneuil ; and we cannot but ad- 

 mire the manifestation of this most scrupulous and sensitive 

 reverence for the labors of his predecessors. 



There is likewise in other families much room for improve- 

 ment in establishing genera and applying characters, in more strict 

 reference to their true meaning. This, perhaps, cannot be done 

 entirely until the true principle of progression among types is 

 fully established, or better understood than at present. 



As American geologists, we are all much indebted to M. de 

 Verneuil for giving us this sketch of his examinations in this 

 country. Coming fresh from his extensive explorations in Rus- 

 sia and the northern parts of Europe, with Sir R. I. Murchison, 

 and with an intimate knowledge of other portions of the conti- 

 nent, and all that had been previously done in the investigation 

 of the palaeozoic strata, no other person could have presented so 

 clear and perfect a coup d'ceil as we have in this paper. 



In concluding this subject, two points of interest present them- 

 selves as of special importance, namely, the line of demarcation 

 between the Silurian and Devonian systems, and that between 

 the Devonian and Carboniferous systems. We have space only 



to glance at the first of these. It appears clearly established, 



judging from the facts advanced and opinions expressed by M. de 

 Verneuil, that the horizon recognized in Europe as the base of 

 the Devonian system, finds its parallel at the base of our upper 

 limestone series of the Helderberg, or at the bottom of the Scho- 

 harie grit. The Oriskany sandstone must remain for the present 

 debatable ground. This horizon, when traced westward, passes 

 through the cliff limestone, leaving its lower part, which is a 

 continuation of the Niagara group, in the Silurian system, and the 

 upper part, corresponding to our Onondaga and Corniferous lime- 

 stones, in the Devonian system. Thus it would appear that we 

 have all doubts removed as to what is recognized as Devonian 

 in Europe, and however disposed we may feel to question the 

 propriety of such subdivision, we are satisfied to know its recog- 

 nized limits. 



It is not a little remarkable, however, that there still exist so 

 many real causes for difference of opinion in relation to the limits 



