34 



XKW \()KK STATIC MrSICTM 



POTSDAM SANDSTONE 



After an enormously long period of existence as a land area, 

 whose duration comprised all the latter portion of Precambric 

 time and most of the Cambric as well, and wdiose history is re- 

 corded in erosion of the Precambric rocks, the eastern margin of 

 the Adirondacks became depressed and deposits commenced to ac- 

 cumulate upon its surface. Thus began the formation of the 

 Potsdam sandstone. 



The deposit began on the northeast and extended both west and 

 south, accumulating in sinking troughs along the line of the Cham- 

 plain and St Lawrence valleys. It is thickest in Clinton county, 

 where the thickness is an unknown amount in excess of looo feet 

 and where the lower beds are unlike those shown elsewhere. These 

 beds are coarse conglomerates, feldspathic sandstones and ferru- 

 ginous, shaly sandstones, wholly without fossils and apparently de- 

 posited above sea level. They are followed above by purer, quartz 

 sandstones, white, gray^ yellow, brown or red in color, mostly very 

 thoroughly cemented and resistant rocks. Above come less firm, 

 somewhat calcareous sandstones, forming the upper part of the 

 formation. In this upper division and in the upper part of the 

 preceding division a scant fauna appears which shows that this 

 portion of the formation is marine. 



It is only this upper division of the formation which is found in 

 Saratoga county. The thickness here does not average in excess 

 of lOO feet, ranging from 50 to 150 feet, the variations being 

 chiefly due to the irregularity of the Precambric surface upon 

 which it was deposited. There is usually foimd a few feet of 

 basal conglomerate, seldom very coarse, above which the formation 

 is imbroken sandstone, the lower half siliceous, the upper cal- 

 careous, in which man.y of the beds weather to an ochreous rotten 

 stone. No fossils w^ere seen by us in the formation on the Sara- 

 toga quadrangle, though Miller found L i n g u 1 e p i s acumi- 

 nata in it on the adjacent Broadalbin quadrangle. 



About Saratoga the most extensive exposures of the formation 

 are those north of the village in Greenfield township. It is also 

 thinly exposed at Corinth. The best continuous section is exposed 

 along a small branch of (llowegee creek, a mile south of East Gal- 

 way. At the base of the section the creek cuts down into the Pre- 

 cambric, exposing a small outlier of this formation. Above this a 

 continuous section 200 feet thick is exposed. The lower 50 feet is 

 chiefly sandstone, with occasional beds of calcareous sandstone ; in 



