Ries — Geology of Orange County. 



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seen at the north end of the Cornwall station of the AVest Shore rail- 

 road. Around the mouths of Moodna river and Quassaic creek, the delta 

 deposits form a large portion of the terrace escarpment. The southern 

 portion of Newburgh is built on the delta deposits of Quassaic creek. The 

 deltas show a characteristic structure and their materials are coarse sand and 

 gravel, with patches of coarser material in places where the currents were 

 swifter. They often overlie the clay to a thickness of from ten to fifteen feet. 



Good sections of the Moodna delta can be seen from the train as it 

 crosses the New York, Ontario and Western railroad bridge about one and 

 one-half miles northwest of Cornwall. The clays underlying the terrace 

 vary in thickness. At Roseton there are 270 feet of clay under the terrace, 

 1()!S feet of which are above river level. The clay is greyish blue and 

 generally weathers yellow in its upper portions. It is often capped by 

 several feet of fine sand and gravel. At New Windsor the clay is yellow, 

 tough, and frequently contains glaciated boulders three to four feet in 

 diameter. Just north of Cornwall, at Hedge's brick yard, the clay at the time 

 of a previous visit by the writer in 1891, showed that peculiar crumpling 

 of a few layers between undisturbed ones, noticed at other localities and 

 described in the Tenth Annual Report of the New York State Geologist, 

 page 1 89. This distortion is produced, either by a slip, or by pressure of the 

 overlying delta deposits. 



Another terrace area begins north of West Point on the southern slopes 

 of Crow's Nest, and continues to a short distance south of the point. 

 The shore line here is 180 feet A. T., and the government buildings are 

 situated on the terrace. The underlying material is mostly boulder till, 

 which is well exposed in the railroad-cut just north of West Point. From 

 West Point to Fort Montgomery there is little evidence of terrace material, 

 probably because the low ridge of gneiss along the river prevented the 

 deposition and facilitated the erosion of much estuary material. 



Of importance among the quaternary deposits of Orange county are the 

 numerous old lake-beds which especially abound in the Hudson river area. 

 The lakes were formed by the damming up of the valleys and depressions 

 between the slate ridges, and they disappeared through the subsequent tilling 

 of their basins or the cutting down of their outlets. Black soil underlies the 

 surface to a depth of from five to fifty feet, and this, according to Mather*, is, 

 in turn, underlaid by marl. 1 was not able to find any evidence of this, either 

 by personal observation or inquiry. The largest of these old lake bottoms is 



* Geology of New York, First District, 1842, page 16. 



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