58 NEW YORK STATE MUSKtM 



The anorthosites have not escaped the general results of 

 squeezing and crushing that are so strongly shown by the 

 gneisses. On the contrary the feldspar crystals in the area of 

 the map are seldom if ever provided with sharp edges. A blue 

 crystalline nucleus is surrounded by a crushed white pulp of 

 comminuted feldspar, phenomena that will forcibly appeal to 

 an observer as having been produced by pressure on a grand 

 scale. They are also drawn out into gneissoid foliation in many 

 instances, but this structure is not specially marked because of 

 the lack of dark minerals, which accentuate it by contrast with 

 the feldspar. Often a narrow rim of pink garnets will be noticed 

 surrounding such dark silicates as appear in the anorthosite. 



The anorthosites in typical development will be found on the 

 west side of Lake Placid, and specially on the hilltop back of the 

 Whiteface Inn. As the Whiteface type they constitute the peak 

 of the same name. They bound the Wilmington valley so far as 

 here mapped, and make up all the central part of the Sentinel 

 range. To the south they become the prevailing rock and beyond 

 the area of the map they form all the high peaks around Mt Marcy. 



Trap dikes. The trap dikes constitute minor but striking mem- 

 bers in the geology of the region. They are not numerous so far 

 as known within the area of the map. They have been met almost 

 always throughout the mountains, where some great fault line 

 has formed a line of w^eakness, up through which they have 

 found an outlet from the reservoirs of molten rock in the in- 

 terior. They are all black basalt and in thin section are shown 

 by the microscope to contain plagioclase feldspar and augite, as 

 the most abundant minerals. Magnetite, apatite and sometimes 

 brown hornblende are also present, and more or less glass. 



A dike occurs about a mile north of Eagle Eyrie. A ramifying 

 and very instructive netw^ork of them is well exposed at the High 

 Fall in Wilmington Notch. Others were noted in the limestone 

 area a mile or so south of the Notch proper. They occur north- 

 west of Clifford Falls on the east slope of Sentinel. In the Cas- 

 cade Notch, immediately opposite the hotel and beneath the 

 ^ cascade ' there is another network of them, and still another in 



