WILLIAM B. DWIGHT. 135 
facts were developed which opposed this supposition. 
The first fact was that the lithological constitution dif- 
fered entirely from that of the Trenton wholly calcare- 
ous conglomerate, in being highly arenaceous, as also in 
the entire lack of the microscopic corals which abound 
in the Trenton. On the other hand, its lithological 
characters are quite in harmony with those of the ad- 
joining ledges known to be Potsdam. 
In the second place, an outcrop of the Hudson river 
shales was discovered close to the western base of this 
hill, within a few feet, thus marking the line as the 
actual western limit of the limestone. This limit is at 
the most but three hundred feet west of the fossiliferous 
Potsdam strata, a space by no means sufficient to allow 
the presence of Calciferous and Trenton strata of the 
usual thickness exhibited in the region. <A further 
study of all the phenomena makes it quite certain that 
the Potsdam extends to the western margin of this belt 
of limestone, in its entire southern extension through 
the district examined. This limestone margin (as traced 
from the north) is broken by three or four jogs, as the 
belt widens to the west, until the field next south of T. 
A. Hinkle’s cottage %s reached ; from that point it is 
nearly straight. Close to this line, at the distance of a 
few feet throughout its entire length, there are many 
outcrops of Hudson river shale which continue west to 
the Hudson river, unless Utica shales may occur at 
some points. The shales are in many places separated 
from the Potsdam limestone by lines of springs and 
ponds, or by dry gullies. From the extreme northern 
end, the plane of contact is marked by a line of ponds 
nearly to Hinkle’s house. Close to this house, to the 
west of it, there isa deep gully, with the limestone on 
which the house stands, on the east, and the shales, 
standing nearly vertical in a bold exposure, on the west. 
This gully continues to mark the line to the southwest 
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