CHEMUNG GROUP. 
253 
The lower beds of this group are well exposed a little south of the head of Seneca and 
Cayuga lakes, and at some distance above their level. The broken margins of the northern 
escarpments, along the whole extent of the district, present good exhibitions of the same ; 
while the water courses along the southern border of the State expose the higher beds, and 
their connection with the rock next above. 
This group requires to be studied at several localities, in order to understand the variations 
in lithological and other characters which it undergoes in its extension westward, as well as in 
passing southward toward the upper termination of the same. 
Along the eastern margin of the district the strata are, as a whole, darker colored, with 
more frequent intermixtures of the shales and sandstones, which less often appear in distinct 
and well-defined beds. The shales are of a dark olive color, and the same for the most part 
pervades the sandy strata, and it is only toward the southern border of the State that well- 
defined courses of black shale are found. As we go westward, this character continues in a 
greater or less degree, and there is little change along the sections from the head of Seneca 
and Crooked lakes southward. 
On the Genesee river we find the limits of the products better defined; the shale often in 
thick beds, of a bright green color, and scarcely interrupted by sandy layers. The sandstones 
at the same time are purer and of a lighter color than those farther east, and less intermixed 
with shaly matter. Several subdivisions can be recognized along this river, which, however, 
are not as clearly defined elsewhere. 
The following section presents the order and character of strata in this line of section : 
112 . 
1. Portage sandstone. 2. Olive shaly sandstone. 3 Black slaty sha’e, with septaria. 4. Green sliale, with grey sandstone. 
5. Grey and olive shales and shaly sandstones. 6 Old Red sandstone. 7. Diagonally laminated sandstone and 
conglomerate. 
On going westward from the Genesee river, there appears to be a constant augmentation in 
the quantity of the green shale, which is often the predominating rock ; though from weathering 
to an olive color, it does not always appear as distinctly. The sandstone strata become less 
perfectly defined in general; though in several places in Cattaraugus county there are some 
thick masses of greenish grey sandstone, very durable, and readily quarried into large blocks. 
In die ravines in Chautauque county, extending toward Lake Erie, the shale still retains 
its green color ; the sandstones are for the most part thinly laminated, and partake of the color 
of the surrounding shale. The dark olive sandstones, like those of Painted-post and other 
places in Steuben county, which are thick and important masses, are recognized in Chautauque 
county only as thin layers of brownish sandy shale containing the same fossils as farther east. 
