growing thinner as it approaches the Hudson River, where 
it entirely disappears. At the northwestern corner, where 
this group enters our county, it is slightly thicker than at 
Bridgeport, on the eastern border, where it leaves the 
county. The greatest thickness is not more than seven 
feet, there being four or five feet of limestone overlying 
some two feet of shale 
There are several places where the group is exposed 
and quarried, although, like the preceding, it is largely 
covered with soil and drift. Nevertheless, as the limestone 
is but a few feet in thickness, and dips toward the south, 
it forms a sort of ledge which can be traced across the en- 
tire county. 
This group can be recognized by its dark blue and 
almost black color, and by its concretionary structure. 
This structure is characteristic of the formation wherever 
it is small in quantity. Geodes are common in the rock. 
They are usually lined with the rhombohedral crystals of 
carbonate of lime. 
The most western exposure in the county is at Diet- 
rich’s Quarry, just west of Lysander. The concretionary 
structure is clearly shown at this place; geodes are very 
abundant, some of them containing crytals of dolomite. 
Although the layers are too thin for a good building stone, 
a neighboring lime-kiln, much dilapidated at present, 
shows for what purpose the rock has been used. 
At Ham’s Quarry, two miles northwest of Baldwinsville, 
we have another exposure. At this place the rock is about 
four feet in thickness, and was used in making neighbor- 
ing culverts on the railroad. This limestone contained 
many fucotdes. 
At Young's Quarry, half a mile northeast of Clay Sta- 
tion, the exposure is not more than two feet in thickness. 
The rock was darker colored than at Ham’s Quarry, neither 
was it as compact and fine grained. A neighboring bridge 
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