§2 NEW YORK STATE MUSEUM 



morphism, they have been subjected to profound erosion so that 

 the present surface represents what once was the deeply buried 

 portion of the strata. As a result of these vicissitudes there is little 

 evidence remaining of the precise structural relations presented by 

 the complex or of the order in which the various members were 

 originally deposited. 



Intrusions of deep-seated rocks, mainly granitic in character, 

 occur within the area. They have a more or less gneissoid appear- 

 ance but not the schistosity of the Grenville gneisses, are prevailingly 

 reddish or gray in color and belong mostly to the biotite and horn- 

 blende varieties of granite. They form bosses of some size and also 

 sills and dikes. In their vicinity the schists and gneisses are in- 

 jected by small offshoots of the granites and their pegmatites which 

 oftentimes assume the appearance of a perfect maze of interlacing 

 veins so that the rock is as much igneous as sedimentary in char- 

 acter. Besides these clearly intrusive granites and granite gneisses, 

 there are frequent bodies of gneiss in the forms of bands and lenses 

 which stand in indefinite relationship to the Grenville and which, 

 like some of the gneisses on the border of the area, must await more 

 detailed study and mapping before they can be definitely classified. 



The crystalline limestone of this area constitutes one of the larger 

 bodies of high-grade calcium limestones found in the State. It is 

 mainly an aggregate of coarse granular calcite, white in color, hold- 

 ing a few included minerals like phlogopite, graphite and pyrite in 

 scattered crystals. The average content in carbonates exceeds 

 90 per cent. Though it is called a calcium limestone, there is always 

 a small amount of magnesia present — from 1 to 3 per cent — 

 and in places it has the character of a dolomite. The change to 

 dolomite takes place rather abruptly but apparently without refer- 

 ence to structural lines that might suggest original variations of 

 deposition. The occurrence of dolomite is, however, quite local 

 and unimportant as compared with the great body of limestone. 

 On the other hand, the limestone shows well-marked zones or bands 

 in which quartz and silicates are abundant and which seem to be 

 the result of impurities included when it was being laid down. A 

 peculiar type is represented by an admixture of white quartz and 

 calcite in nearly equal proportions, the two minerals occurring in 

 alternating seams, lending the appearance of a schistose rock, or 

 else in grains and masses thoroughly intermingled. Contact effects 

 with the intrusive granites are manifested in the development of 

 silicate minerals like tourmaline, vesuvianite, pyroxene, tremolite 



