68 NEW YORK STATE MUSEUM 



the magmas were being intruded under deep-seated conditions. 

 Such pressure against the country rock, combined with the usual 

 development of differential flowage, particularly in the magmatic 

 borders, would readily account for the peripheral foliated zones 

 which were produced, no doubt, during a late stage of magma con- 

 solidation. But the conditions for magmatic pressure and flowage 

 must often have varied considerably, and thus the local variations 

 in degree of foliation and granulation are accounted for. 



The gabbro-diorite dikes are also more or less foliated, their 

 borders particularly so. As in the gabbro stocks, 'so here, the folia- 

 tion is considered to have been due to differential magmatic flow- 

 age under moderate pressure during a late stage of magma con- 

 solidation. In these dikes, however, the foliation was developed 

 parallel to the strike of the dikes because cross-sections of the 

 magma chambers were long and narrow rather than rounded or 

 elliptical as in the gabbro stocks. 



Faults 



General features. Faults are neither so numerous nor so promi- 

 nently developed as is usually the case in the eastern and south- 

 eastern Adirondack region. Within the Lake Placid quadrangle 

 the faults are not sharply defined earth- fractures, but rather they 

 are zones of excessive jointing in which more or less crushing and 

 faulting of the rocks have taken place. These broken-rock zones 

 are relatively straight for considerable distances, in some cases for 

 some miles. It seems clear that such alignments of crushed-rock 

 zones are due primarily to faulting, probably multiple faulting. 

 The width of the fault zones is commonly from 25 to lOO feet or 

 more. Most of them strike from northeast-southwest to north- 

 south as usual in the eastern half of the Adirondack area. Because 

 the rocks are broken up into numerous small blocks, the crushed 

 zones form belts of weakness along which valleys (sometimes deep 

 and narrow) have been developed. Little or no positive evidence 

 regarding the positions of upthrow and downthrow sides could be 

 obtained. 



Wilmington notch fault. This i^ the finest example of a shat- 

 tered-rock zone definitely known within the quadrangle. Its length, 

 as indicated on the geologic map, is about 5 miles. The deep, nar- 

 row Wilmington notch, the gorge at High fall, and the gorge at 

 The Flume, all owe their existence to rapid erosion along this 

 prominent zone of weakness. In preglacial time the river did not 



