124 NEW YORK STATE MUSEUM 



The granite, with the exception of the very granular sorts as noted 

 above, is a serviceable stone for all general construction purposes. 

 It has no ingredients to cause discoloration or decay with the lapse 

 of time. Its durability, when subjected to mere weathering, can 

 scarcely be inferior to ordinary granite, though of course it has not 

 the same ability to withstand abrasion or wear, on account of its 

 tendency to cleave along the foliation planes. The many buildings 

 in Yonkers and vicinity that have been constructed of this stone are 

 evidence of its good quality as a structural material. 



Microscopic examination. The mineralogy of the granite is 

 simple ; feldspar, quartz and biotite are the components in order of 

 their relative importance. The feldspar is divided between ortho- 

 clase and microcline, with a little plagioclase. The quartz has a 

 bluish tint and with the biotite often lends a decided bluish cast 

 to the cleavage surfaces, whereas the color across the foliation is 

 prevailingly pink, like that of the feldspar. Under compression, the 

 quartz has developed into lenticular or spindle-shaped individuals, 

 while the feldspar has been corroded and broken down into small 

 irregular particles. 



The subordinate constituents include hornblende, iron oxide, 

 titanite, and zircon. Sulphides appear to be absent from the mass 

 of the rock. There is little change noticeable in the thin sections, 

 except a slight kaolinization of the feldspars and separation of small 

 amounts of iron from the biotite. 



The rock is fine to medium in grain. The lines of foliation 

 marked by the biotite are mostly spaced from 4 to 10 mm apart. 



Quarry development. Quarry work in the Yonkers belt has 

 been carried on for a long time, but until about twenty years ago. 

 did not reach any considerable proportions. Eckel states that most 

 of the quarries operative at the time of his report were opened 

 around 1892. At that time, and in the few subsequent years, there 

 was unusual activity in building and engineering construction, par- 

 ticularly by the railroads, which had a great deal of work in con- 

 nection with bridges and retaining walls under way. The market 

 for stone, however, was mainly local, and with the completion of 

 these improvements the demand so declined as to compel the closing 

 of many quarries. The present outlet is principally for building 

 stone, as illustrated by many public and private structures in 

 Yonkers and vicinity, also in partly dressed condition for founda- 

 tion work, and as blocks and crushed stone for road improvements. 



