106 Barrande, Logan and Hall 



ARTICLE VII. — Correspondence of Joachim Bakrande, Sir 

 William Loqan and James Hall, on the Taconic System 

 and on the age of the Fossils found in the Hocks of Northern 

 New England^ and the Quebec Group of Hocks, 



{From the American Journal of Science No, 92, 1861.) 



I. Introductory Remarks. 



As some of our foreign readers may not be acquainted with 

 the question to which the following important correspondence 

 relates, we think it advisable to make a few explanatory observa- 

 tions by way of introduction. A complete history of the whole 

 subject would require a greater amount of space than can be 

 afforded, and we shall therefore touch only upon a few of the more 

 salient points. 



The rocks under discussion occupy a belt of country east and 

 west from twenty to sixty miles wide, stretching from the vicinity 

 of the city of New York in a northerly direction to Lake Cham- 

 plain and thence through Vermont and Lower Canada to Cape 

 Gasp6 at the mouth of the St. Lawrence. The strata, consisting 

 of slates, limestones, sandstones and conglomerates are greatly 

 disturbed, plicated and dislocated, and are often, especially along 

 the eastern side of the belt, in a highly metamorphic condition. 

 On this side they are overlaid unconformably by Upper Silurian 

 and Devonian rocks, but on the western and northern margin they 

 are in contact with and in general seem to be a continuation of 

 the Lower Silurian. Some of the slates of the formation closely 

 resemble in lithological characters those of the Hudson River 

 group, and thus along the western side of the region, where the 

 junction of the two formations occurs, it is often almost impossi- 

 ble to draw the line between them. The dip and strike of both 

 are in the same direction, and throughout extensive areas the 

 newer rocks appear to plunge beneath the older. The whole 

 district affords an excellent example of those cases, so well 

 known to field geologists, where the true relations of the different 

 masses cannot be clearly worked out without the aid of fossils, 

 and where the best observers may arrive at diametrically 

 opposite opinions. 



Dr. Emmons, one of the geologists of the New York Survey, 

 early convinced himself by a careful examination of these rocks, 

 that they constituted a distinct physical group more ancient than 

 the Potsdam sandstone, the latter being regarded by him as the 

 base of the Lower Silurian System in North America. His 



