256 GEOGNOSY OF THE APPALACHIANS. [XIII. 



Thus we see that at an early period the rocks of the Taconic 

 system were, by Kogers and Mather, referred to the Champlain 

 division of the New York system, a conclusion which has been 

 sustained by subsequent observations. Before discussing these, 

 and their somewhat involved history, we may state two ques- 

 tions which present themselves in connection with this solu- 

 tion of the problem. First, whether the Taconic system, as 

 denned by Emrnons, includes the whole or a part of the Cham- 

 plain division; and, second, whether it embraces any strata 

 older or newer than the members of this portion of the Xew 

 York system. With reference to the first question it is to be 

 remarked, that in their attempts to compare the Taconic rocks 

 with those of the Champlain division as seen farther to the 

 west, observers were led by lithological similarities to identify 

 the upper members of the latter with certain portions of the 

 Taconic. In fact, the Trenton limestone, with the Utica 

 slates and the Loraine or Hudson Eiver shales, making to- 

 gether the upper half of the Champlain division (in which 

 Emmons, moreover, included the overlying Oneida and Medina 

 conglomerates and sandstones), have in New York an aggregate 

 thickness of not less than three or four thousand feet, and offer 

 many lithological resemblances to the great mass of sediments 

 at the western base of the Green Mountains, to which the 

 name of Taconic had been applied. It is curious to find that 

 Emmons, in 1842, referred to the Medina the Eed sand-rock of 

 the east shore of Lake Champlain, since shown to be Potsdam ; 

 and, moreover, placed the Sillery sandstone of the neighbor- 

 hood of Quebec at the summit of the Champlain division, as 

 the representative of the Oneida conglomerate ; while at the 

 same time he noticed the great resemblance which this sand- 

 stone, with its adjacent limestones, bore to similar rocks on the 

 confines of Massachusetts, already referred by him to the 

 Taconic system.* 



This view of Emmons as to the Quebec rocks was adopted 

 by Sir William Logan, when, a few years afterwards, he began 

 to study the geology of that region. The sandstone of Sillery 



* Geology of the Northern District of New York, pp. 124, 125. 



