M W 70HK MI HTM 



i. and the Cambro-SiluriaD (of 

 W, county) yield the beal dolomites. 



PROSPER JIN* . 



considered in prospecting are topography, 

 ation and ap] outcrops. 



rule weather quite readily, but the presence 

 of impurities may exert an important influence in this respect. 

 Pure 1 1 1 1 1 < luble in carbonated water, consequently, 



when a bed o pure Limestone is inclosed between two harder 



ikflj dipping at high angle, the limestone may be dissolved away, 

 ring a valley between the more resistant layers. This fact 

 is often noticed in Westchester county, where the section involves 



. and an overlying mica schist; the beds 



much folded, and the dip is often steep. Most of the 



valleys in this county exhibit gneiss on one side and mica schist 



the other, while the intermediate limestone has been cut down 



by weathering to form a valley. (PI. 2) 



ay lin. mtain sandy layers or chert nodules, or in 



some c ilicified -. In such instances the weathering of 



tremely irregular, the lime carbonate being dissolved 



out, while the Bilicified portions stand out in bold relief on the 



Limes of great purity, however, may 



at tin.' ther unevenly, Bolution for some reason not well 



Understood, taking place along certain lines, thus producing a 



reticul inward from the surface 



of the rock. 



dan limestom carbonate of lime is dissolved out, 



whi i yield- but Blowly to solution, 



rock breaks down into a series of sand- 



The Guelph limestone of western New York shows 



er, owing to the coarsely crystalline 



ability, disinl rather than decompose, 



