402 Review of the Progress of 
which both in Lake Champlain and in the Mississippi valley is 
characterized by primordial types. The intermingling of Pots- 
am and Calciferous forms to which we have already alluded, 
seems however to show that it will be difficult to draw any well 
defined zoological horizon between the different portions of these 
lower rocks, which at the same time offer as yet no evidence of 
any fauna lower than that of the Potsdam. So that we regard 
the whole Quebec group with its underlying Primordial shales 
as the greatly developed representative of the Potsdam and Cal- 
ciferous (with perhaps the Chazy), and the true base of the Silu- 
Tlan system. 
The Quebec group with its underlying shales is no other than 
the Taconic system of Emmons. Distinct in its lithological 
characters from the Potsdam and Calciferous formations as devel- 
oped on Lake Champlain, Mr. Emmons was led to regard these 
strata as belonging to a lower or sub-Silurian group. We have 
however shown that the palwontological evidence afforded by 
this formation gives no support to such a view. To Mr. Em- 
mons is however undoubtedly due the merit of having for a long 
time maintained that the Taconic hills are composed of strata 
inferior to the Trenton limestones, brought up into their present 
position by a great dislocation, with an upthrow on the eastern 
side. We would not object to the term Taconic if used as indi-, 
cating a subdivision of the Lower Silurian series, but as the name 
of a distinct and sub-Silurian system it can no longer be main- 
tained. The Quebec group evidently increases in thickness as 
we proceed toward the south, and the calcareous parts of the 
formation are more developed. In 1859, I visited in company 
with Mr. A. D. Hager the marble quarries of Rutland and Dor- 
set, in Vermont. The latter occur in a remarkable synclinal 
mountain of nearly horizontal strata of marble and dolomite, 
capped by shales, and attaining a height of 2700 feet above the 
railway station at its base. I then identified these marbles with 
the limestones of the Quebec group, considering them to be be 
of chemically precipitated carbonate of lime or travertine, and 
not limestones of organic origin. | 
_ The existence of great dislocations in the Appalachian chain 
is amply illustrated in the sections of Prof. Rogers, and in those 
given by Safford in Hastern Tennessee, where by the aid of 
fossils it becomes comparatively easy to trace them. See the 
Map accompanying his Geographical Reconnaisance of Tennessee, 
1855; where the magnesian limestones of formation IV, are 
shown to be not only brought up on the east against the Upper 
Silurian and Devonian, but even to overlap the black shales at 
1e of the Carboniferous system. It is remarkable to find 
that as parly.as 1822, the idea of a great dislocation of this nature 
in Eastern New York was maintained by Mr. D. H. Barnes in 
pred dis of Canaan mountain. (This Journal, [1], v, pp- 
