276 
GEOLOGY OF THE FOURTH DISTRICT. 
Localities of Superposition. 
There are few localities, where the junction of this group with the one next above is obvious. 
Throughout the greater part of the district, the higher rocks have been removed by denudation. 
In a few points, it is succeeded by a thin band of the Old Red sandstone, which is a highly 
ferruginous stratum, and contains few fossils. In other places, the conglomerate of the Coal 
formation rests directly upon the Chemung group. 
The section, page 253, shows the order among the rocks of the Chemung and the successive 
formations along the Genesee river. The same is seen in the section of Allegany county, 
Plate 11. In Plate 10, the section across Steuben county shows the Old Red succeeding the 
Chemung. In Plates 11 and 12, the sections of Cattaraugus and Chautauque counties show 
the conglomerate resting upon the Chemung group. This occurs from the thinning out of the 
Old Red sandstone, as will be seen under the description of that rock. 
The series even where the Old Red intervenes is nevertheless incomplete ; and the perfect 
order of succession from this point upwards cannot be established in New-York, from the 
absence of the Carboniferous limestone. 
With the rocks of the Chemung group, terminate all those included in the New-York 
System. The reasons for uniting all the rocks and groups below the Old Red sandstone in 
one system, and for considering the latter as distinct, have already been stated briefly. The 
termination upwards of the Chemung group has been shown in the sections given, and the 
character of the strata composing it fully described. It will be seen, that in the eastern part 
of the State, many of the fossils of the Hamilton group extend into the Chemung, and at the 
same time the lithological character is nearly the same in both. Farther to the west and 
southwest, the lithological character of the two groups is quite different, and at the same time 
we find few of the fossils of the lower group extending into the higher. Even where there 
is the greatest distinction in lithological and fossil characters, the two can only be separated as 
parts of a great system, being the productions of continually operating causes from beginning 
to end. The products differ in character, and the fossils are of different species, but they are 
of the same prevailing genera. 
Where the best opportunities for examination exist, the change from the Chemung to the 
Old Red sandstone is abrupt in character. The greenish and olive shales and sandstones 
charged with Strophomena, Deltliyris and Atrypa, are succeeded by a red sandstone, con¬ 
taining none of the organic remains of the lower rocks. The change in lithological character 
is accompanied by a change- in the fossils, even more decided. Few shells are known, but 
the rock every where contains the remains of fishes, which are often preserved in a very 
perfect manner. 
It is quite evident from lithological character alone, that these two deposits are not syn¬ 
chronous ; the materials differ in character, and the extent of the higher rock is very limited. 
The Old Red sandstone is scarcely known west of the Genesee river, where the Chemung is 
