1866.] 251 [2^"- 



In these remarks, 1 have not intended to express an opinion of the 

 generic value of certain characters, but merely to show, as it appears 

 to me, a gradual or successive development in certain parts, which 

 finally becomes so wide a departure from the characters of typical 

 forms of Spirifera, that it deserves especial attention. Nor can we 

 deny that this progressive development of the septum and its modifi- 

 cations keeps pace and corresponds with the geological succession ; 

 reaching its extreme state, so far as now known, in the Carboniferous 

 period. 



In our investigations of the Chemung group in its more easterly 

 extension in the State of New York, it has proved, throughout the 

 greater part of its thickness, to be comparatively barren of animal 

 organisms, though often containing an abundance of the remains of 

 land vegetation. As we progress westerly, the coarser sediments have 

 given place to finer materials, or are more or less intercalated with 

 shales or shaly and calcareous beds, while the coarser beds exhibit 

 less resemblance to shore deposits, and we find an increasing number 

 of animal remains both of the Brachiopoda and Lamellibranchiata, 

 though there are usually few of any other class. But these are not 

 equally distributed, either vertically or horizontally. 



There is one fact, however, which can scarcely fail to impress the 

 collector of fossils in this group of strata, which is, that in going 

 westward, certain forms which are abundant in some localities be- 

 come rare or disappear altogether, so that sometimes localities not 

 very far removed from each other give almost entirely a different set 

 of species. Certain species which are common in Schoharie, Broome, 

 Tioga and Chemung Counties, I have not seen in Cattaraugus and 

 Chautauque Counties ; while many species which are common in the 

 western counties are quite rare or unknown to me in Tioga, Tompkins, 

 and the counties east of these. Although we may attribute this view 

 in some part to our imperfect collections, it is nevertheless in a great 

 degree true. 



Reasoning upon the nature and origin of the sediments as well as 

 upon these observed conditions, we might expect to find a changing 

 fau 'a as we recede from the ancient coast line furnishing these 

 matt rials, and which were then swept into the wide ocean to the 

 westward. While in some of the more eastern localities we find 

 specie") of the Hamilton group apparently mingling with those of the 

 Chemung group, the higher beds of Cattaraugus and Chautauque 

 Counties give us an association of fossils having a more carboniferous 

 VOL. X. — 2h 



