114 THE CAMBRIAN. [bull. 81. 



Dr. Emmons in 1842. As the typical Potsdam sandstone in this dis- 

 trict is an extension of the sandstone of the Adirondack sub-area within 

 its borders, the review of its literature will be united with that of the 

 typical Potsdam of the Adirondack district. 



The occurrence of the Upper Cambrian or Potsdam zone as distinct 

 from the Georgia slate and " Red Sandrock," is spoken of in the de- 

 scription of the section crossing the town of Georgia, Vermont, 1 where 

 mention is made of the discovery of a fauna closely related to that of 

 the Upper Cambrian. This is the same horizon referred to on page 17, 

 par. 14. 



In a description of a section crossing the typical Taconic area of 

 eastern New York and western Massachusetts by Mr. C. D. Walcott, 2 

 the typical Potsdam sandstone is not recognized. It is stated that cer- 

 tain shales designated as Terrane No. 2, may represent the Potsdam 

 terrane, or it may be represented by the lower part of the limestones 

 of Terrane No. 3, or the upper part of the Quartzite of Terrane No. 1. 



CANADIAN EXTENSION. 



The Canadian extension of the Northern Appalachian District is from 

 the United States boundary northeast to the vicinity of Point Levis, 

 Quebec, on the western side of the extension of the Green Mountain or 

 Sutton Mountain anticlinal, and from Quebec down the south shore of 

 the St. Lawrence River to Cape Rosier, Gaspe\ On the eastern side of 

 the anticlinal the supposed Cambrian rocks of New Hampshire, cross- 

 ing the southeastern portion of the province of Quebec, to the Maine 

 boundary, are also included. 



The first notice of the rocks, subsequently referred to the Cambrian 

 in the vicinity of Quebec, was by Dr. J. J. Bigsby. 3 He divided the 

 strata into three series. First, the slaty series, composed of slates and 

 grauwacke, occasionally passing into a brown limestone, and alternat- 

 ing with calcareous conglomerate in beds, some of which are charged 

 with fossils ; second, the limestone series ; third, gneiss. In the beds 

 of this conglomerate on the south side of the St. Lawrence he noticed 

 the presence of trilobites, encrinites, corallines, and other fossils. He 

 considered them above the supposed equivalent of the Carboniferous 

 limestone of the English geologists. 



In his description of the succession of the strata at Montmorenci 

 Falls, Dr. E. Emmons states that the rock forming the falls is a gneiss, 

 and in the figure illustrating the section the Potsdam sandstone is shown 

 resting unconformably upon the gneiss and subjacent to the Trenton 

 limestone, but with a conglomerate between it and the Trenton lime- 

 stone. 4 He subsequently correlated the sandstones that are extensively 



1 Walcott, C. D. Second contribution to the studies of the Cambrian faunas of North America. U. S. 

 Geol. Survey, Bull. No. 30, 1886, p. 19. 



8 The Taconic System of Emmons and the use of the name Taconic in Geologic nomenclature. Am. 

 Jour. Sci., 3d ser., vol. 35, 1888, p. 240. 



8 On the geology of Quebec and vicinity. Proc. Geol. Soc, London, vol. 1, 1827, p. 37. 



•Geology of the Montmorenci. The American Magazine, vol. 1, 1841, p. 148. 



