92 Mr. T. Sterry Hunt 



sandstone, which both on Lake Champlain and in the Mississippi 

 valley is characterized by primordial types. The intermingling of 

 Potsdam and Calciferous forms to which we have already alluded, 

 seems however to show that it will be diflScult to draw any well 

 defined zoological horizon between the different portions of these 

 lower rocks, which at the same time offer as yet no evidences 

 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 

 Calciferous (with perhaps the Chazy), and the true base of the 

 Silurian system. 



The Quebec group with its underlying shales is no other than 

 the Taconic system of Emmons. Distinct in their 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 how- 

 ever shown that the palseontological evidence afforded by this 

 formation gives no support to such a view. To Mr. Emmons 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 indicating a sub- 

 division of the Lower Silurian series, but as the name of a distinct 

 and sub-Silurian system it can no longer be maintained. The 

 Quebec group evidently increases in thickness as we proceed to- 

 wards the south, and the calcareous parts of the formation are 

 more developed. In 1859, 1 visited in company with Mr. A. D. Ha- 

 ger the marble quarries of Rutland and Dorset, 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 beds 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 Eastern Tennesse, where by the aid of fossils it 

 becomes comparatively easy to trace them. See the Map accom- 

 panying his Geological Reconnaissance of Tennessee^ 1855; where 

 the magnesian limestones of formation IV, are shown to be not 



