Ce et a eS a ee. FT ee Oa 
ies sae 
yore 
_ &fe represented as existing in immense force in Western Vermon t this is 
_ ne ods in the Hudson River formations, which really belong 28 
s —T shall indicate, to another lias ae eg? 
J. B. Perry on the Geology of Vermont. 343 
limits, has been estimated by Dr. Hitchcock, and others as 
having a thickness of not less than 10,000 feet. We accord- 
ingly have for the thickness of the second great division of the 
Primordial rocks from 20,000 to 25,000 feet, and for that of 
the two great divisions thus far considered from 25,000 to 
30,000 feet. 
Leaving the Potsdam Sandstone out of view for the present, 
we may notice the thickness of the succeeding beds in their 
typical localities. That of the Calciferous Sandrock is about 
et; that of the Chazy Limestone is nearly the same ; 
While that of the Birdseye is only 30 feet, and that ot the La 
Mott, or Black River, 15 feet. The Trenton Limestone is 
some 400 feet thick, the Utica Slate about 75 feet, while the 
train Shales may reach 700 feet.* This estimate gives us 
seh than 2,000 feet as the aggregate thickness of all these 
rocks, 
_We have now only to place the immense force of the Taco- 
nic rocks in parallelism with the thickness of the Lower Silu- 
tian formations, to see at once the striking disparity. Would 
we also take them up, bed by bed, and look at them in con- 
trast, we should discover how utterly impossible it is to bring 
them into codrdination. But time fails me now to enter into 
the details of any such comparison. 
We may next notice the relation of the Potsdam Sandstone 
of Vermont to the formations under consideration. 
A band of Red Sandstone runs northerly and southerly 
through most of Western Vermont, and may be seen in places 
testing on the Black or Swanton Slates. Portions of this rock 
were long ago described by Dr. Emmons as Potsdam Sandstone. 
Most geologists, however, regarded it as of Medina age, and 
regard 
to the subjacent slate falls to the ground. That there may 
be no doubt on this matter, and as some still persist in assert- 
ing that the Black Slates are Hudson river, the Potsdam beds 
having been shoved, or folded over upon them, I will refer to 
some evidence having a bearing on the subject, and calculated, 
agen figures, as should be — are to be ae oS ee at 
imati i is of comparison. 7 ; 
. oat gecnie’ shidteasas bak ect ascribed to some of these beds, ose 
’ by ‘ counting 
endeavor to indicate 
