Hies — Geology of Orange County. 



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mately parallel and form an.angle of fiO to TO 4 -" with the dip. Overlying the 

 Hudson river shales with a slight unconformity, is the Oriskany quartzite 

 which forms numerous ledges along the western face of this ridge. It is a 

 hard, fine-grained grey or brown quartzite, traversed by numerous cracks 

 which break the rock into angular fragments and surround each outcrop with 

 a characteristic pile of debris. 



The rock is sometimes massive, at other times well bedded, giving a 

 strike of N. 25° E. and dipping -10° S. E. At such points it contains slaty 

 or shaly layers, which, however, seem to be rather the result of shearing 

 action than sedimentation. On the eastern side of this ridge the quartzite is 

 hard, tine-grained, massive, and of a light red color, traversed by numerous 

 milk-w hite streaks of quartz. There are about 100 feet of the quartzite in 

 this ridge. 



On the western side of the ridge, the relations of the quartzites to the 

 Hudson river shales are probably, as previously mentioned by Darton, those 

 of an overthrust, since the Helderberg limestone, which underlies the 

 quartzite at several localities in this belt, is missing, and the outcrops of 

 the quartzite and shales are so close together that there is no room for the 

 limestones. 



To the west, the Oriskany passes conformably under the Monroe shales, 

 the two being separated by only a narrow valley. 



The Monroe shales are well exposed along the road from the valley 

 of Seely's brook to Monroe, and along the "dug road, 1 ' crossing the hill 

 w est of Long pond, which is south of Monroe. They are not infrequently 

 fossiliferous, and at times resemble in appearance the Hudson river shales. 



Geologic Relations of the Area along Skunnemunk Mountain. 



From Monroe northeastward, the great synclinal fold of Devonian rocks 

 extends as a high ridge nearly to Cornwall, where it ends somewhat abruptly. 

 The southw estern end of the mountain is a gentle syncline, w hile the north- 

 east end is similar, except that on the eastern side of the mountain the strata 

 curve over and downward, forming an overthrown anticline. 



The crest of the mountain is formed of the Skunnemunk conglomerate, 

 the characters of which have been already noted. It begins near the Seven 

 Springs Mountain house, on the ledges a little to the northeast of it, and 

 extends along the two crests of the mountain, giving rise to steep cliffs and 

 rocks' slopes. A considerable depression lies betw een the two crests, and its 

 northern end is occupied by Barton swamp. The conglomerate is about 300 



