40 NEW YORK STATE MUSEUM 



Granite porphyry. A bodiy of coarse, usually porpliyritic, 

 granite occupies about 25 square miles of the northern portion of 

 the quadrangle. Feldspar crystals nearly always range in length 

 from one-fourth to i inch, and usually these stand out conspicu- 

 ously as phenocrysts. Quartz individuals are often one-fourth to 

 three-fourths of an inch long. Dark minerals seldom make up more 

 than 10 or 12 per cent of the rock. 



Most of the granite porphyry is more or less gneissoid, but locally 

 there are considerable bodies of the rock which are practically 

 devoid of foliation and not 'much granulated. Such nonfoliated 

 rocks occur in big exposures on the hills in several square miles 

 of the northwestern corner of the map area, on Fremont hill, an^ 

 on the two hills respectively 2 and 3 miles east of Fremont hill. 

 At the other extreme mere are considerable developments of highly 

 gneissoid coarse granite and granite porphyry. In these facies 

 the feldspars are generally highly granulated, with the larger ones 

 more or less flattened out into lenselike eyes or so-called " augen." 

 The quartz crystals in these very gneissoid phases are remarkably 

 flattened out into thin lenses, sometimes nearly an inch long. Fine 

 examples of flattened quartz may be seen in the ledges from one- 

 half to I mile southwest of Franklin Falls, i^ miles north of 

 Woodruff fall, and three-fourths of a mile north-northwest of West 

 Kilns. The flattened quartz crystals are always arranged with long 

 axes parallel to the foliation. In some localities the degree of 

 foliation varies greatly within small areas. Thus, on the hillock 

 ij4 rniles southeast of Fremont hill, nonfoliated, moderately foli- 

 ated, and highly foliated coarse granites are associated. Similar 

 variations in foliation occur on the hilltop i mile east of the south 

 end of Silver lake. 



The coarse granite very commonly weathers to a pink or pinkish 

 gray, and more seldom to light brown. Fresh rock was obtained 

 in but few localities as, for example, from a ledge recently blasted 

 open by the roadside one-half of a mile southwest of Franklin 

 Falls. Such rock is greenish gray. Whether or not much, if any, 

 of the fresh granite is pink could not be determined. 



The mineralogical composition of the granite porphyry is well 

 illustrated by no. 46 of table 2, which represents a thin section 

 of the typical, fresh, very gneissoid rock with large granulated 

 " augen " of feldspar and highly flattened quartz individuals. This 

 rock differs from the granite porphyries described by the writer 

 from the central and southern Adirondacks by the absence of micro- 

 cline, though possibly this mineral does occur in other portions of 



