204 THE CAMBRIAN. [bull. 81. 



■\ 



CAMBRIAN SYSTEM (SEDGWICK). 



Olive sandstone and slate Fucoides setra (Brong.) 



Variegated sandstone (Potsdam sandstone of Emmons) Dictuolitcs radians 



A description of the geographic distribution of the Potsdam sand- 

 stone in Clinton County is given by Dr. Emmons in the third annual 

 report of the New York State survey. He also describes its strati- 

 graphic character and appearance, and states that at Flat Rock the 

 sandstone is more or less a conglomerate and coarser than at Potsdam 

 or Keeseville. 1 



A description of the Potsdam sandstone as it occurs on the western 

 side of the Adirondacks, in Jefferson County, is given by Dr. Emmons 

 in his fourth annual report, as follows: 2 



Lying unconformably upon the primary is the Potsdam sandstone. It is there- 

 fore next in the series. It is a firmer rock, more crystalline, and less porous than 

 the same rock in St. Lawrence, and especially that belonging to Potsdam. ' 



The only fossil found in it was a small linguloid shell called Lingula 

 ovata? 



The presence of the Potsdam sandstone in Lewis County is noted by 

 Mr. Lardner Vanuxem, who states that the sandstone appears in the 

 northeastern part of the county in low ridges, with all the characteristics 

 given by Prof. Emmons, in whose district it is an extensive rock. 4 



The Potsdam sandstone as it occurs in Washington County, upon 

 the eastern side of the mountains, is described by Dr. W. W. Mather as 



a bard, siliceous sandstone, white, red, gray, yellowish, and frequently striped. It 

 is well developed at Whitehall, where it has a thickness of 150 to 200 feet. It extends 

 up the valley of Wood Creek in a southerly direction by Coinstock's Landing, 1 mile 

 east of Fort Ann, and so on farther south, diminishing in thickness and becoming 

 interlaminated with finer-grained strata of grits, slates, and shales. Some of the 

 strata of this rock are covered with the most beautifully characterized ripple-marks, 

 as perfect as if just formed on the sand of a sea beach, while the rock is of the most 

 indurated kind of sandstone. 5 



The only fossils noticed were fucoidal impressions. 



The geographic distribution of the Potsdam sandstone about the Adi- 

 rondacks is shown on the map of 1844 that accompanies the final report 

 of the State geologists of New York. On a geological map of the Mid- 

 dle and Western States by Prof. James Hall 6 the main geographic dis- 

 tribution is indicated and a small area on the southern side of the Wis- 

 consin River in Wisconsin is the same tint as the Potsdam area of New 

 York 



1 Third annual report of the second geological district. Third annual report of the geological sur- 

 vey of New York, 1839, pp. 231, 232. 



2 Fourth annual report of the survey of the second geological district of New York. Fourth annual 

 report of the geological survey of New York . Albany, 1810, p. 322. 



3 Op. cit,,p 323. 



4 Fourth annual report of the geological survey of the 3d district. Fourth Report of the Geological 

 Survey of New York. Albany, 1840, pp. 363, 368. 



6 Fifth annual report on the geological survey of the 1st geological district. Fifth Annual Report of 

 the Geological Survey of New York, 1841, p. 102. 



6 Geological map of the Middle and Western States. Geol. of New York. Report on the Fourth 

 (Jeol. district, Albany, 1843. 



