102 ~—Billings on the age of the so-called Potsdam Rocks 
But the most important and interesting locality is 14 miles 
east of Swanton, discovered by the Rev. J. B. Perry and Dr. G. 
M. Hall. The black slates holding Paleophycus inctpiens, Obo- 
lella cingulata, Orthisina festinata, Camerella antiquata, Paradox 
ides Thompsoni, P. Vermontana and Conocephalites Teucer, are here 
seen conformably interstratified with the Red sandrock. Four 
of these species occur in the limestone which immediately over 
lies the sandstone with S. linearis on the north shore of the 
Straits of Belle Isle, and it therefore seems quite clear that the 
rocks of these two localities (860 miles distant from each other) 
are of the same age. 
Taking all these facts together scarcely anything more is neces 
sary to show that the Red sandrock of Vermont is of the age 
assigned to it by me from the examination of the Conocephalites 
at Highgate in July last. The independent discoveries of Mr. 
Richardson at Belle Isle and of Dr. G. M. Hall 
d by what appears to be a whitish magnesian limestone. 
This place has been several times described, but what struck me 
as particularly worthy of notice, is that the under side of the 
limestone, where it is in contact with the slate is smoothed, pre 
senting very much the appearance of slickensides. I infer from 
this that either there is a fault here, or, that the limestone has 
moved on the surface of the slate. The limestone appears to be 
either Potsdam or Calciferous. 
nake and Buck mountains have often been appealed to by the 
advocates and opponents of the Taconic System. The first mel 
tioned of these two hills is capped by sandstone and magnesial 
is thrown oh so that its base is 700 feet above the Trento® 
Rare In this I think he is right, but the rock which a 
of a mile from its northern extremity, and found the sandstone 
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