436 TACONIC ROCKS. 



him, announcing the discovery of numerous primordial forms in the Quebec group 

 at Point Levi (equivalent of the red sandrock in Vermont.) In accordance with these dis- 

 coveries the Canada Survey have given up their former theory that the Quebec group is 

 middle Silurian, and agree with Emmons in calling it lower Silurian. Logan thinks the 

 Georgia slates may be subordinate to the Potsdam sandstone, and may more truly represent 

 the primordial zone in Canada. He differs from Prof. Emmons in not regarding the slate 

 under the red sandrock in Vermont as Primordial, but of the age of the Hudson River 

 group. But throughout Canada, where Prof. Emmons finds many Taconic rocks, Logan 

 finds nothing lower than lower Silurian. Many have supposed that great aid was given 

 by these discoveries to the advocates of the Taconic system ; but there is surely little of 

 comfort to them in Sir William's conclusions. 



Prof. Jas. Hall opposed these conclusions of Sir Wm. E. Logan, holding that the strat- 

 igraphical evidence was in favor of regarding the Quebec group as middle Silurian, just 

 as Logan had held, and that the evidence of Primordial age was not so clearly implied by 

 the fossils, as was the position of the second fauna. 



GENERAL CHARACTER OF THE TACONIC ROCKS IN VERMONT. 



The Taconic- rocks in Vermont are the following, being divided into an upper and lower 



series. 



Upper Taconic Rocks. Thickness in feet. Lower Taconic Rocks. Thickness in feet. 



Black slate, "] Magnesian slate, 2,000 



Taconic slate, ( ^n QAA Stockbridge limestone, 2,000 



Roofing slate, Granular quartz rock, with 



Sparry limestone, J associated talcose beds, 1,200 



25,200 



The upper Taconic rocks are the Georgia slate ; the rnagnesian slatejincludes the talcoid 

 schists and talcose conglomerates ; the Stockbridge limestone is the Eolian limestone ; 

 and the granular quartz, etc., is the quartz rock of this Report. Lithologically the differ- 

 ent members are as follows : The black slate is a clay slate, often highly calcareous. The 

 Taconic slate is an even-bedded, alluminous slate, varying from the finest possible grit to 

 one that is coarse and rather uneven-bedded, and passing into a rock having many of the 

 characters of a sandstone. Its prevailing color is pea green. Its name is derived from 

 that of the whole system, which is derived from the Taconic range of mountains in West- 

 ern Massachusetts. The roofing slate is only a variety of the Taconic slate suitable for 

 economical purposes. Its colors are every shade of green, chocolate, red, gray and dark 

 brown. It is the Taconic and roofing slates which make up the great thickness of the 

 System. They are best developed in Rutland County. 



The term sparry limestone is not a good one, because it can be applied to many rocks 

 belonging to other groups. The distinctive limestone of this member has a bluish color 

 through which there run numerous seams of white calcite, checking it in various ways. 

 Or the rock may be gray and almost black, and it may be traversed by veins of quartz. 

 This member is distinctly characterized by its interstratification in 1 >ods from twenty to 

 two hundred feet thick, with the Taconic slates. It is not, therefore, a distinct part of Hie 

 series, like the Potsdam sandstone in the Champlain group. In general the sparry lime- 

 stone may be said to be any bed of limestone in the upper Taconic series. 



