QUARRY MATERIALS OF NEW YORK 113 



ing of soil and detritus over the low ground that intervenes between 

 the exposures. 



Owing to the prevalenee of plagioclase among the feldspars 

 represented, the Peekskill granite shows a relatively high pro- 

 portion of soda as compared with most granites and appears to be 

 genetically allied with the diorites of the Cortlandt series. This 

 feature, as well as the field relationships already mentioned, lends 

 support to the view expressed by Berkey 1 that the granite repre- 

 sents but a phase of the Cortlandt invasion and not a separate 

 body; it constitutes the acid extreme of the series which in the 

 other direction range through diorite, gabbro and norite to rocks 

 like pyroxenite and peridotite that are destitute of quartz and feld- 

 spar. 



The granite like the typical Cortlandt rocks, is thoroughly mas- 

 sive in texture, lacking evidences of strong compression and the 

 gneissoid development which are so common among the Precambric 

 and early Paleozoic rocks of this section. Its intrusion occurred 

 therefore after the period of regional metamorphism that marked 

 the close of Lower Siluric time — the last stage in the general 

 metamorphism of the region. The contact of the granite with the 

 country rocks is very generally concealed, but inclusions that ap- 

 parently represent the bordering schists are not infrequent and 

 sufficiently establish the nature of the contact relations in that 

 respect. The latest of the country schists belong to the Hudson 

 River series. The inclusions mostly in evidence are amphibolites 

 and dark hornblende schists which undoubtedly came from some of 

 the earlier and underlying formations. . 



The view expressed as to the common derivation of the granite 

 and the Cortlandt rocks can not be supported by observations in 

 regard to their mutual contact relations, as such information was 

 not procurable when the writer visited the locality. There seems 

 to be complete similarity, however, in their attitude with respect to 

 the crystalline schists, and the field evidences, so far as they go, 

 are indicative of a geologically contemporaneous intrusion for both 

 granite and gabbros. 



Mohegan Granite Company's quarries 



The quarry property of the Mohegan Granite Company is situated 

 a little east of the Cortlandt township line in Yorktown, West- 

 chester county, on the southwestern slope of a prominent ridge 



3 Science, 28 : 575, 1908. 



