walcott.] ADIRONDACK SUB-PROVINCE. 205 



In a tabulation of the Lower Silurian strata of the State of New York, 

 published in 1842, Prof. T. A. Conrad states that the Cambrian system 

 has proved to be the Lower Silurian, and he places the Potsdam sand- 

 stone at the base of the latter system, beneath the Calcifeious saud- 

 stoue. 1 



The final report of the geology of the second geological district con- 

 tains a summary by Dr. Emmons of the characters of the Potsdam sand- 

 stone as found in the counties of Warren, Essex, Clinton, Franklin, St. 

 Lawrence, and Jefferson, and also gives details of the formation as 

 found in each county. 2 A description of the formation in detail and 

 also a general descriptive summary of the formation is given by Mr. 

 Lardner Vanuxem as it occurs in his district, 3 and Dr. W. W. Mather 

 describes it as it occurs in Washington County and in Saratoga County. 4 

 Prof. James Hall describes it concisely in an account of the rocks of 

 New York State. In its geographic distribution the rock is known in 

 Canada, on Lake Superior, and, from its position, it is probably the 

 same that appears on the Mississippi River mentioued by Dr. Owen in 

 the report on the lead region of the northwest. 5 He also identifies it 

 with No. 1 of the Pennsylvania survey, or a sandstone extending through 

 New Jersey, Pennsylvania, and Virginia. 6 



In the account of his travels in North America Sir Charles Lyell de- 

 scribes the Potsdam sandstone as he saw it at Au Sable Chasm, near 

 Keeseville, Essex County, New York. He speaks of it as a siliceous 

 sandstone: 



In many places, this most ancient of the fossiliferous rocks of New York (the Pots- 

 dam sandstone) is divided into laminae by the remains of innumerable shells of the 

 geuus Lingula. They are in such profusion as to form black seams like mica, for 

 which th«y were at first mistaken. With the Lingula occurs anothor placunoid shell 

 allied to, if not identical, according to Prof. E. Forbes, with a fossil which occurs in 

 company with a small Lingula in the lowest beds of the English Silurian series at 

 Builth, in Brecknockshire. 7 



A general account of the Potsdam sandstone is given by Dr. E. Em- 

 mons in the Agriculture of New York. It is an excellent summary of 

 the general characters of the formation. 8 



. The Potsdam sandstone of Lewis County is described by Mr. F. B. 

 Hough in a general manner. He states that it thins out to an unim- 

 portant stratum as compared with the formation in St. Lawrence County ; 

 also that the superjacent Calciferous sandrock is represented by only a 



1 Observations on the Silurian and Devonian systems of the United States, with descriptions of new 

 organic remains. Phila. Acad. Sci. Jour., vol. 8, 1842, pp. 229, 230. 



2 Geology of New York, part 2, second geological (northern) district, pp. 102-105, 177-179, etc. 



3 Geology of New York, part 3, third geological (central) district, Albany 1842, pp. 28, 29. 



4 Geology of New York ; geology of the first (southeastern) district. Albany, 1843, p. 418. 



6 Geology of New York ; geology of the fourth (western) geological district. Albany. 1843, p 27 

 6 0p.cit.,p.28. 



7 Travels in North America. New York, 1845, vol. 2, pp. 131, 132. 

 •Agriculture of New York, vol. 1, 1846, pp. 117, 118. 



