WITH THE NEW-YORK SYSTEM. 
57 
The summit is marked by rather rounded hills, of sufficient magnitude to break the con¬ 
tinuity of the plain. One of these hills, nearly east of the ferry, is crowned by the Cal- 
ciferous sandstone: it has a sugarloaf shape; descending, however, more rapidly upon its 
western face. Through this hill the section passes; and here we find the taconic slate 
outcropping upon the western side directly beneath the limestone, and but a few feet 
distant from it. Some diversity of opinion may arise in relation to this small mass of 
limestone being the Calciferous. My reasons for regarding it as such, are, 1st, It is litho¬ 
logically so: it is geodiferous : its geodes contain the quartz crystals and the peculiar 
anthracite; and, 2dly, a few of the fossils are either those of the Calciferous or the Chazy 
limestone, for I have found the Maclurea here. Then again its position is that of the 
Calciferous sandstone: it is the inferior rock where the Potsdam is absent. But at this 
locality we find other fossils quite similar to those of the Trenton limestone ; the Bellero- 
phon bilobata , or the same which is credited to the Trenton limestone. But what is quite 
remarkable, I found masses bearing the character of the Birdseye limestone. All these 
facts put together indicate that this mass of limestone is a mixture of all the lower lime¬ 
stones of the New-York system; that they meet in this mass, though it is by no means 
extensive. But this view is not adverse to the position I take, namely, that the slate 
beneath is older, and belongs to an older system, inasmuch too as it is unconformable to it. 
An interesting fact is exhibited at Whitehall, in the position or relations of the Potsdam 
sandstone. At this place it may be traced continuously to the gneiss on the western side 
of the mountain, and dipping to the east. We trace it upward into the calciferous sandstone, 
whose thickness here is at least two hundred feet. But a mile or two to the east we find 
in the deepest ravines the outcropping of the black or taconic slate, which plunges rapidly 
downwards on the western face of the rock. Now it is highly probable that the slate is 
continued farther west than what appears in the outcrop, so that it probably passes beneath 
the Potsdam unconformably, as we know it does beneath the prolonged Calciferous sand¬ 
stone. If this view is correct, the lower member of the New-York system, the Potsdam 
sandstone, rests or reposes upon two systems : on the western margin, upon gneiss, and 
the Primary system; and on the eastern margin, upon the Taconic system. 
But an important inference may be drawn from the relations of the potsdam at this place, 
namely, that it is not the granular quartz of which much has been said in the Reports of 
Prof. Hitchcock, and in the geological papers of Prof. Dewey, or No. 1 in part of the 
Pennsylvania and Virginia Reports. I say in part , because Professors Rogers in their No. 1 
include both the Potsdam sandstone and the Granular quartz; for if these masses are one 
and the same, the slate one and a half miles east ought to rest upon the Calciferous sand¬ 
stone ; and there is no space for the slate to come in between the calciferous and potsdam, 
as they are conformable to each other, and the whole western face of the hill or mountain 
is an exposed cliff, where every inch of rock from top to bottom can be seen. At this 
place, it is true, there is a thin band of siliceous slate ; but it is in toto distinct from the 
argillaceous slate a short distance to the east. This band is an accidental deposit: it is 
sometimes present, but frequently absent; while the argillaceous or green taconic slate is 
[Agricultural Report.] 8 
