i!22 PROCEEDINGS OF THE AMERICAN ACADEMY 



on the coast of St. Anne, where there is a group of Upper Taconic 

 slates corresponding to the " Swanton slates," but of a much greater 

 thickness, — at least 5,000 feet, instead of the 2,400 feet of the en- 

 virons of Swanton. 



In the town of Quebec even, at the Saut du Matelot, at the citadel, at 

 Beauport, at Charlesbourg, and below Montmorency's fall, the schists 

 have the same aspect and composition with the " Swanton slates," black, 

 sometimes gray, even reddish ; they contain some layers of blue lime- 

 stone, lentils or kidneys of limestone, enclosed in the schists, and 

 which at the Saut du Matelot resemble erratic limestone blocks shut 

 into the black schists. They seem to be almost entirely destitute of 

 fossils, except near the base, where are found the celebrated compound 

 GraptoJitcs. 



In order to complete the general theoretic section of the Taconic, 

 2,500 feet, that is to say double the thickness of the " Swanton slates" 

 as they are seen at Swanton, must be added. 



The dislocation of the Potsdam resulted in the isolation and uncov- 

 ering of a certain surface of these deposits of sandstone, -conglomerate, 

 dolomite, and limestone. This uncovered portion has been exposed to 

 the great denudation which took place afterwards ; the lowest jmrts 

 alone remain ; all the rest have been carried off. This explains why 

 the Potsdam, or " Red Sandrock," in Vermont is only the lowest part 

 of the formation. But in certain isolated cases portions have been 

 less denuded, protected by divers obstacles, varying according to the 

 localities : and here and there the Potsdam or " Red Sandrock " is 

 quite thick. 



One of these uninjured portions, preserved one might almost say 

 miraculously, is near Saratoga, where it has been discovered by ]\Ir. 

 C. I). "Walcott, who has described a part of the fossils he discovered, 

 in the Thirty-second Annual Report of the New York State Cabinet. 

 This upper part of the "Potsdam group" is formed of a " massive 

 limestone," according to Walcott, containing a primordial fauna anal- 

 ogous to the Potsdam of Wisconsin. These are some of the forms : 

 Linfjula, PlatyceraSy Metoptoma, Crepicephalus, Lonchoccjjhalus, Dike- 

 locephalus, and Ptychaspis. (See Science, Vol. III. No. 52, p. 136.) 



This upper limestone of the Potsdam covers the sandstone of Keese- 

 ville (Au Sable Chams), and the red sandstone of Higiigate (Church 

 farm). 



This important discovery in this typical region of the Taconic 

 completes the series of all the beds of this great and important system. 

 The objection of the non-existence of this limestone formation under 



