86 NEW YORK STATE MUSEUM 



injection and development of silicates. The structure is very vari- 

 able, the quality is quite erratic and the grain is prevailingly coarse. 

 On account of these facts, the rock is not so serviceable as the others 

 for the ordinary higher grade purposes. It was, in former. years, 

 burned for lime and was used also in connection with local iron 

 smelting ; but it has not been worked now for many years. A very 

 large development of this limestone is found in Sprout Brook valley, 

 however, and any special quality belonging to this type could be 

 produced on a large scale. 



Lime. In earlier days lime was produced from certain of the 

 limestones in this area. At present no lime burning is practised 

 although certain beds of the Inwood are used in this way at Ossin- 

 ing, a few miles farther south. Undoubtedly similar quality of 

 product can readily be made from the limestone of this quadrangle, 

 but a high-grade quality to meet the competition in the market is 

 not likely from any of these formations. 



Quartzite. A belt of quartzite approximately 600 feet thick 

 extends along the east margin of Peekskill hollow for many miles. 

 This is the Poughquag quartzite belonging to a down-faulted block. 

 It stands almost exactly on edge and its southern exposure is in a 

 hill at least 100 feet high, not far from the Hudson river. It is 

 almost an ideal location for working, but nothing has been done 

 beyond investigating the quahty. It is a high-grade quartzite rock 

 carrying only a very small percentage of impurities and has been 

 examined on this account for its possibilities as a glass sand. These 

 results have been reported by R. J. Colony in a recent bulletin of the 

 New York State Museum^** in which the following analysis of a 

 mixed sample is recorded : 



Si02 95 ■ SI "^^ 



Fe=03 0.27'/' 



ALO. 2.35% 



CaO 0.07% 



Ti02 o.39'/r 



Mr Colony notes that not all the silica in this rock is quartz, how- 

 ever, that feldspar grains are numerous and no doubt these grains 

 are the chief source of the alumina. 



Similar or even better quality is to be found on the north margin 

 of the quadrangle where the Poughquag is exposed. None of 

 these occurrences, however, is so well situated as that at Peekskill 

 creek for cheap transportation arid unless a very high-grade quality 



"N. Y. State Mus. Bui. 203-4, P- 22 (1919) ; also p. 8-9. 



