14 PALiEONTOLOGT OF NEW- YORK. 



some localities in Canada, especially bordering the north side of the St. 

 Lawrence and Lake Ontario*. 



We shall, probably, yet find it convenient to indicate several subordinate 

 divisions in the Trenton limestone, where that rock is best developed, 

 marked by the prevalence of certain species, and the almost entire re- 

 striction of these species within narr<Jw limits. 



The group of strata known as the Hudson-river group, which in its 

 more extended signification may include all the beds from the Trenton 

 limestone to the Shawangunk conglomerate, has afforded in New- York 

 but small additions to the number of fossils previously known in this 

 formation. From the metamorphic slates of this group on the western slope 

 of the Green mountains in Vermont, we have three or more species of 

 trilobites, which are of much interest, being representatives of a genus 

 but little known in this country. The slates of the same age farther to the 

 south have yielded some additional new species. 



• In gome parts of Canada the fossils of the Trenton limestone are completely silicified ; and the shells 

 thus preserved are often weathered out so as to show their characters of hinge, etc. almost in the same 

 perfection as in modem shells. The same result is accomplished by dissolving away the limestone by acids, 

 leaving the silicified shell entire. In this manner specimens have been obtained, showing the characters of 

 hinge and teeth, in Tellinomya, Modioloptis, ^mbonychia and others. These characters are such as to 

 leave no doubt regarding the true relations of these fossils. 



The Genera Tellinoxta and Hodiolopsis have been referred by M. D'Orbiont to Ltonsia, and the 

 species are placed under that genus in his " Prodrome de Pal6ontologie." The distinctions between these 

 genera were originally founded, chiefly, upon external characters; but we now have the means of shovring 

 the internal characters of these shells, which prove them not only entirely distinct, but in both instances 

 widely different from Lyomia. Tlie former proves to be closely allied to Nucula (and will include several 

 species previously arranged under that genus) ; all the species examined having a continuous series of 

 Crennlations along the hinge line, and an external ligament, while the species of Modiolopsit have no serial 

 teeth or crenulations of this kind in the hinge. 



The Genus Ambonychiu, regarded by M. D'Orbiost as equivalent to Potidonomya of Bbonn, proves 

 to be quite as distuict from the latter as Tellinomya is from the former. 



In the mean time, a writer, professing to give an account of the present state of American geology, has 

 copied the list of fossils from the work of M. D'Orbiony (acknowledging his indebtedness to tliat author 

 for a corrected Iht of iimericcn /ostih), entirely regardless of the relations of these and otlier fossil 

 genera; and, obtaining possession, without authority, of illustrations made for the author's o'wn work, he 

 baa carelessly used them to propagate these false impressions concerning the fossils of the rocks of New- 

 York and the United States. But for this circum.stance, the present writer would not have animadverted 

 npon the jumbled production which its author has had the lelf-complaceQCy to designate by the com- 

 prehensive title of "American Geology " ! 



