GEOLOGY OF LAKE PLEASANT QUADRANGLE 35 



seen at the time of the writer's study, but its presence, together 

 with the practically horizontal position of the strata, make the 

 mapping of the Potsdam here quite certain. 



Where the branch road comes close to the river about four- 

 fifths of a mile north of the north end of the village, there is 

 a small sandstone outcrop belonging with either the Potsdam 

 or the Theresa, most likely the former. The rock is a two-foot 

 bed of white sandstone with a westward dip of lo degrees. As 

 far as one-half of a mile northward from this outcrop along 

 the same road, several large angular fragments of sandstone were 

 noted. 



Along the river west of the village no ledges of rock of any kind 

 occur, though we have every reason to believe that the Potsdam 

 occurs there under cover of Pleistocene and later Paleozoic strata. 



The Potsdam almost certainly comes against the north base of 

 West hill but heavy drift conceals all ledges there. 



Theresa beds. These beds are distinctly transitional in char- 

 acter between the Potsdam sandstone and the Little Falls dolomite. 

 They consist of alternating sandstone and dolomite beds, the former 

 being in every way like the Potsdam sandstone and the latter like 

 those of the Little Falls dolomite to be described next. Numerous 

 exposures may be seen along the face of the rock terrace just east 

 of the village. No single exposure shows a thickness greater than 

 10 or 12 feet but, since all are well distributed between the 1040 and 

 1 100-foot contours and the strata show only a very slight westerly 

 dip, we can be sure of a total thickness of 60 feet for these beds. 

 The thickest dolomite bed noted was 14 inches. Near the fault at the 

 southern end of the area of Theresa, the beds strike north 30° 

 east and dip 20° west, which is doubtless due to the updrag effect 

 along the fault. Northeast of the village no outcrops could be found, 

 but there can be no doubt of the existence of the Theresa there as 

 shown on the map. No other outcrops of this formation occur 

 within the valley, but if the Pleistocene deposits were removed it 

 would outcrop as a practically continuous belt along most of the 

 length of the outlier to the west of the small fault in the valley 

 bottom. 



Little Falls dolomite. The only exposures of Little Falls 

 dolomite are to be found capping the rock terrace just east of the 

 village. There are so many outcrops that much of the area shown 

 on the map is solid rock at the surface, the dolomite beds showing 

 only a very slight westward dip. Since the outcrops range from 



