320 C. D. Waleott — The Taconic System of Emmons. 



fault line separating the Cambrian and Silurian Terranes ; and 

 the shales west of the fault belong to the Silurian, not to the 

 " Upper Taconic " Terrane. The line of outcrop of the Cam- 

 brian Terrane is Avell marked, and I have endeavored to locate 

 it accurately on the map. The great Appalachian fault sepa- 

 rates the Potsdam and other Silurian rocks from the Cambrian .; 

 and nowhere on the western side of the Cambrian Terrane, to 

 my knowledge, either in New York or Vermont, is there a 

 deposition contact, either conformable or unconformable, be- 

 tween the rocks of the " Taconic System " and the Potsdam or 

 other Silurian terranes. I have examined all the localities 

 cited by Dr. Emmons and, later, by Professor Marcou and, in 

 every case, the great fault separates the strata of the two sys- 

 tems. In fact, the Taconic usually rests on the Silurian strata 

 as the result of the overthrust from the east ; and, as will be 

 shown in my report on Washington County, N. Y., the strong- 

 est proof of the presence of a fault line is shown by the me- 

 chanical disturbance of the Cambrian strata, on the eastern 

 side of the fault. 



That the Taconic slates are unconformably pre-Potsdam, is 

 yet to be proven in any area known to Dr. Emmons, either in 

 New York or Vermont. Where they pass beneath the shale 

 representing the Potsdam horizon, beneath the Stockbridge 

 limestone in the Taconic Range, they are conformably pre- 

 Potsdam, but this fact was unknown to Dr. Emmons.* 



Resume. — As the result of these comparisons, we find that 

 the " Lower Taconic " is essentially a repetition of the lower 

 Silurian (Ordovician) section of the Champlain valley. It differs 

 in lithologic details and in having a less abundant fauna in the 

 typical Taconic area 



The " Upper Taconic " is found to be conformably subjacent 

 to the " Stockbridge" limestone of the "Lower Taconic, 1 ' and 

 to include the Potsdam horizon at or near its upper portion. 

 Its base is not unconformably subjacent to the Lower Silurian 

 Terrane, as maintained by Dr. Emmons and Professor Marcou. 



The value of the paleontologic identification by Dr. Em- 

 mons of the "Upper Taconic" slate as a pre-Potsdam forma- 

 tion will now be considered. 



* Professor Henry P. Rogers, in his address before the meeting of the Asso- 

 ciation of American Geologists and Xaturalists, held at Washington, in May, 

 1844, said, when speaking of the unconformity claimed by Dr. Emmons between 

 the Champlain and Taconic rocks : " I must take the liberty of expressing my 

 disbelief of any such unconformity, and of observing that in the prolongation- 

 southwestward of this altered and plicated belt as far as the termination of the 

 Bine Ridge in Georgia, a distance of 1000 miles, no interruption of the general 

 conformity of strata has ever met the observation of my brother or myself." — 

 (Amer. Jour. Sci., I, vol. xlvii, p. 152, 1844). 



