773 NEW YOEIv STATE MUSEUM 



western portions of the county are a continuation of the Orange 

 county Cambro-Silurian limestone belts. The former are meta- 

 morphosed limestones and partake of the nature of marble, being 

 highly crystalline, while the latter are not. 



The eastern helt. While there are outcrops of the limestone 

 at a number of points in the valley followed by the Harlem rail- 

 road, only two large openings have been made. These are at 

 Dover Plains and South Dover. 



At Dover Plains, G-. & J. H. Ketcham have operated a quarry 

 along the highroad one half mile southeast of the town. The 

 rock is a soft, fine grained dolomite of gray or white color. The 

 opening is about 200 feet long, 20 to 30 feet wide and 10 feet 

 deep. 'Eo analysis was made of the stone but several samples 

 were examined to determine their insoluble matter, which ran 

 from 2 to 3;^. - 



The South Dover marble co. has a large quarry (pi. 34) on the 

 hill 2|- miles northeast of the station. The rock is a fine grained, 

 white dolomite and has hitherto been used only for structural 

 purposes. It has to be hauled to the railway. In appearance it 

 is very free from impurities. The following analysis of the rock 

 was furnished by the superintendent of the company. 



Silica , 7 



Ferric oxid 25 



Alumina 37 



Lime 30.63 



Magnesia. 20 . 25 



Soda . .12 



Potash 46 



The stone is brought down to the railroad over a private trolley 

 line. 



The limestones in the western part of the county are usually a 

 hard, fine grained bluish gray rock, containing less magTiesia than 

 the whiter phases to the southeast and east. It has been used 

 for lime but on the whole is so silicious that the resultins; lime 

 would be lean. 



