QUARRY MATERIALS OF NEW YORK I43 



the thinly foliate gneiss and the massive granite. Within the limits 

 of one quarry, however, material is found that is fairly uniform. 

 It fills all the requirements for rock faced ashlar, as it is strong, 

 durable and quite attractive if somewhat somber of tone. 



Pegmatitic granite in Orange county 



Within the Precambric belt of Orange county, which includes 

 most of the Highlands area west of the Hudson river, occur numer- 

 ous outcrops of coarse, reddish granite of pegmatitic nature. This 

 rock is differentiated from the surrounding gneisses that form the 

 main mass of the Highlands by its coarser grain and also by its 

 more massive appearance, never showing the well-developed par- 

 allel arrangement characteristic of the latter. The feldspars reach 

 a diameter of an inch or even more when uncrushed, and are 

 inclosed in a finer mixture of granular feldspar and quartz, so as 

 to lend the aspect of a porphyritic rock. The feldspar in the ground- 

 mass is the result largely of the breaking down of the larger in- 

 dividuals under compression, the uncrushed remnants having a 

 rounded or lenticular cross-section. The predominant variety is 

 red microcline, but there is also more or less of white or greenish 

 plagioclase. Of dark silicates the rock carries very little ordinarily. 

 On the other hand, magnetite is a common ingredient, and epidote 

 appears quite often as an alteration product. By reason of the 

 varied colors imparted by the feldspar, magnetite and epidote the 

 granite not infrequently possesses ornamental qualities which make 

 it serviceable for decorative work and it has been employed locally 

 for that purpose in fireplaces, mantels etc. Unfortunately it does 

 not occur in large enough bodies to be quarried on a commercial 

 scale. 



The granite may be seen in the form of stringers, dikes and 

 irregular bodies which intersect the gneiss and are probably off- 

 shoots of some magma that has penetrated the country rocks from 

 below at a time when the metamorphism of the latter had been 

 completed. The same magma is possibly represented in the bosses 

 of granite outcropping on Mount Adam, Mount Eve and Pochuck 

 mountain in southern Orange county. ' The magnetite mines are 

 situated mainly in belts of gneiss that have been injected by the 

 granite, and afford good specimens of the fresh material. At the 

 Forest of Dean mine back of West Point a very attractive variety 

 occurs in contact with the magnetite, and there is a large amount 

 of it on the mine dump. ' 



