WITH THE NEW-YORK SYSTEM. 57 



The summit is marked by ratlicr rounded hills, of sufficient magnitude to break the con- 

 tinuity of the plain. One of tlioso hills, nearly east of the ferry, is crowned by the Cal- 

 ciferous sandstone : it has a siigarloaf shape ; descending-, however, more rapidly upon its 

 western face. Through this hill the section passes ; and here we find the taconic slate 

 ontcropping 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 bilohata, 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 hinidred 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 quaitz 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 clifi", 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 ^ 



