no NEW YORK STATE MUSEUM 



existence of a granitic facies among its highly differentiated repre- 

 sentatives, might be regarded perhaps as suggestive of some relation 

 with that invasion which took place as late at least as Siluric time. 



A comparison of the Garrison and Peekskill granites shows that 

 they resemble each other only in regard to color and their uniformly 

 massive habit. The former is a representative of the normal alkali 

 class of granites characterized by a preponderance of the potash 

 feldspar over the lime-soda varieties ; the Peekskill rock on the other 

 hand shows by its high content of plagioclase an affinity with the 

 diorite-gabbro series and, strictly considered, is to be classed as a 

 quartz monzonite. The Garrison boss, also, is distinguished by a 

 fine cataclastic texture, while the samples of the Peekskill granite 

 seldom show any appreciable effects of pressure metamorphism. 

 These features point more or less clearly to a separate, independent 

 source of the two intrusives and the prior age of the Garrison boss. 



The granite has been quarried quite extensively for building stone 

 and foundation material, for which purposes it is very well adapted. 

 The main opening is known as King's quarry, operated, at one time 

 by the King Granite Co., and later by Doern & Sons of New 

 Rochelle. 



Some of the buildings erected from material secured at this 

 quarry are : St Joseph's Church, Tremont av. & Washington St., 

 New York ; Guard House at West Point ; powder magazine on lona 

 island in the Hudson river ; and a school building in Tarrytown. 

 The property has not been worked extensively for the last few 

 years 'and probably will not again be a very active producer. The 

 granite boss, however, extends out on the adjoining lands, so that 

 other quarries may be operated in the future. A site already pros- 

 pected is found just south of King's quarry on the land of Raymond 

 Moore of Peekskill. 



Field characters. The general structure and quality of the 

 granite are best shown at King's quarr)^ which covers perhaps half 

 an acre of surface and has a face up to 50 feet high. The principal 

 structural feature is lent by the jointing which is well developed, 

 especially the sheet joints. The latter divide the exposed rock into 

 elongated horizontal lenses that are from i to 3 feet thick in the 

 middle but increasing in size as depth is attained. The sheets are 

 inclined slightly toward the northwest. Three sets of steeply in- 

 clined joints also occur, of which the most prominent strikes north 

 and south and dips 70° east; another set strikes N. 40° W. and 

 dips 70° southwest ; and the third strikes east-west and dips 60° 

 north. The rift is stated to be about parallel v/ith the first set. 



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