Cusiiing — Geology of Clinton County. 



549 



though on the north flank of Arnold hill, in the vicinity of the gneiss, coarse 

 conglomerates occur. In the central part of the town it runs down in a 

 curious way between tw r o gneiss ridges. There is here a drift-filled valley, a 

 mile or more in width, which runs clear across the township, and was 

 apparently the track of a pre-glacial stream. Along the Ausable it intervenes 

 between the Clintonville gneiss and the gabbro to the eastward, but further 

 north, gneiss ridges form both walls. At the north end, the Potsdam-gneiss 

 contact is found near Mr. Harkness's house. The well on the premises, close 

 by the house, penetrated hornblende gneiss at a depth of a few feet, while 

 only five rods to the northwest, flinty Potsdam was reached in a cistern. One 

 mile and a half to the southward, are two old openings in Potsdam sandstone, 

 known as Mace's quarry. The rock is ordinary hard, massive, buff sandstone. 

 Less than a mile away on each side, are massive gneiss ridges, and we have 

 here apparently a pre-Potsdam as well as a pre-glacial valley. It is unfor- 

 tunate that the drift covering does not permit us to determine how far up 

 this valley the Potsdam runs, but there seems no reason why it may not run 

 clear to the Ausable river. It recalls the patches of Potsdam described by 

 Kemp from Essex county.* 



Series VI. The northern slopes of Arnold hill are covered with till, 

 and the surface is plentifully besprinkled with boulders. The till covering 

 ranges throughout the gneissic area, but elsewhere in the township every- 

 thing of the sort is hidden from sight beneath the universal mantle of sand. 

 This surrounds Halleck hill on the east and north, running clear to the lake 

 shore and well into Peru. It extends up the Ausable valley beyond the 

 limits of the township, and at Clintonville and New r Sweden is heavily banked 

 up against the gneisses, is bare and much drifted about by the winds. It 

 also extends throughout the valley of the Little Ausable, even in its narrow 

 upper reaches, great drifts of it lying around and against the protruding 

 bosses of gneiss. 



Peru. 



The western third of Peru township is hilly, and occupied by the 

 gneisses. A plain of till, with a breadth of one mile and a half, borders the 

 hills on the east. Then there is a drop of fifty to one hundred feet, to the 

 level of a sand plain, which has a breadth of from three to four miles. For 

 the last three miles to the lake, rock ledges protrude frequently through the 



* Report of New York State Geologist for 1858, Vol. I., pp. 454-158. 



