518 
PALAEONTOLOGY OF NEW YORK. 
clecl 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. 
AH 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 
Hamilton group, 
Corniferous limestone 
Oriskany sandstone. 
