QUARRY MATERIALS OF NEW YORK 121 



cut in that direction lend a mottled aspect. The quartz and feldspar 

 are in granulated condition, probably the result of compression 

 upon what originally were large crystals but are now finely com- 

 minuted. There is some limonite stain in zones about the mica. 



The granite at this quarry appears darker when observed in mass 

 than the average of the other quarries. It would be classed as 

 medium gray, with a pinkish tone, the pink being fairly decided in 

 places. 



As a variant of the Peekskill granite boss may be mentioned an 

 outcrop which lies but a few rods to the east of the Roberts quarry 

 and undoubtedly is a part of the intrusion. It is characterized by 

 the abundance of mica, much greater in amount than observed in 

 the rock elsewhere. The color as a consequence is quite dark. 

 From microscopic examination the feldspar appears to be almost 

 entirely plagioclase and to predominate largely over the quartz. 

 The rock 'by itself would be classed as a granodiorite, and the oc- 

 currence serves to bring out the close relation that probably exists 

 between the granite and the more basic types which constitute the 

 Cortlandt series proper. The ledge is too small to have any im- 

 portance for quarry purposes. 



THE YONKERS GNEISSOID GRANITE 



A light-colored granite with a markedly foliate texture is found 

 in southern Westchester county where it is the basis of rather ex- 

 tensive quarry operations. Under the name of the Yonkers gneiss 

 it has been described by Merrill and others and its igneous derivation 

 clearly established. The fact, however, that the foliated appearance 

 in the main is not the result of secondary recrystallization or meta- 

 morphism, but an original feature imparted during the first consol- 

 idation of the magma has not been generally recognized. On ac- 

 count of this fact it seems more appropriate to call the rock granite 

 than gneiss, the latter term implying, as it does, the effects of 

 metamorphism. 



According to the recent work of Berkey, the Yonkers is probably 

 to be classed with the early Precambric series of intrusions which 

 are represented in the Highland region by the Storm King boss. 

 It seems to be confined to thin sills which are intrusive in the 

 Fordham gneiss. The development of the parallel arrangement of 

 the constituents may be explained as the effects of compression 

 exerted during the intrusion of the granite while it was still in a 

 condition of mobility, facilitated by the relatively thin mass of the 

 granite. There is little in the way of secondary crystallization as 



