956 PALEONTOLOGY OF NEW- YORK. 



Brachiopoda and Laniellihranchiata, though there are usually few of any other 

 class. But these are not equally distributed, either vertically or horizontally. 



Theje 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 become 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 Chenumg 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. Al- 

 though 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 fauna as we recede from 

 the ancient coast line furnishing these materials, and which were then swept 

 into the wide ocean to the westward. While in some of the more eastern localities 

 we find species of the Hamilton group apparently mingling with th6se of the 

 Chemung group, the higher beds of Cattaraugus and Chautauque counties give 

 us an association of fossils having a more carboniferous aspect than those of the 

 higher beds in the eastern counties of the State. 



As we proceed farther to the westward, these differences become more and more 

 marked; and in connexion with the contemporaneity of the sedimentary forma- 

 tions in distant localities holding dissimilar species, we must consider the gradual 

 lithological changes which have affected the character of the fauna. There can be 

 no longer any question that the higher arenaceous and argillaceous formations of 

 New-York and the adjacent portions of Pennsylvania and Ohio, when traced in a 

 southwesterly direction, become intercalated with calcareous bands; while the 

 coarse sediments give out, or are replaced in a great degree by calcareous or 

 argillo-calcareous deposits, containing some of the same species of fossils, with 

 an accession of other forms adapted to the changed conditions of life.* 



In the extreme southwestern extension of the Palteozoic series, the interval 

 between the Upper Helderberg group and the Coal Measures, which in the North 

 is occupied by the Hamilton, Portage, Chemung and Catskill formations con- 

 Btiluting so marked a feature in New- York, Pennsylvania and Ohio, is there filled 

 by calcareous accumulations that have been considered, as belonging exclusively to 



• I have already shown a similar condition existing at the period of the Coal Measures ; where some 

 calcareous bands of a few feet thickness in Ohio, Pennsylvania and Virginia, become expanded so that, 

 together with the associated calcareous shales, they embrace almost the entire formation tow.irds the 

 Rocky Mountains and in the far west and southwestern regions of the United States and in Mexico. 



