518 PALEONTOLOGY OF NEW YORK. 



ded in the underclay, showing that the ocean bed had been elevated above the 

 sea level for a considerable period of time. This horizon is probably the 

 equivalent of the lower part of the Oneonta series, and may be regarded as 

 of Hamilton age. The influx of these shore deposits into an area occupied by 

 marine sediments and a marine fauna has, for a considerable extent westward, 

 and through a considerable time, broken the continuance of the marine fauna, 

 though gradually mingling with the succeeding marine deposits in its western 

 extension. 



The Oneonta sandstone in Otsego and Chenango counties, is succeeded directly 

 by strata bearing fossils of Chemung age, leaving no question as to its relations. 

 All the more recent investigations serve to show that the views heretofore ex- 

 pressed regarding the position and relations of this formation are correct, and 

 that properly it forms no part of the Catskill group, except so far as it is the 

 result of similar conditions which were intermitted at the close of the Oneonta 

 and resumed after the deposition of the Chemung sediments, and which may 

 have once been continuous in some far easterly locality. Moreover, with our 

 present knowledge, the higher beds of the Chemung, as known in the central 

 and western portions of the State, have no considerable extension to the east- 

 ward. The fossils obtained on the western flank of the Catskill mountains are 

 comparable with those of the middle portion of the group as developed in 

 central New York. Thus far I am not aware that the Chemung group has 

 been positively shown to exist on the eastern flank of the Catskills, and 

 the rapid thinning of that formation to the eastward, as shown on the geological 

 map, suggests the possibility of it having thinned out entirely before reaching 

 the Hudson river valley. 



Catskill group, 

 Chemung group. 



Portage group, 



' Hamilton (Upper), 

 Hamilton group, 

 Corniferous limestone, 

 Oriskany sandstone. 



