GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 45 



mountain mass rising very steeply for more than 2000 feet above 

 the lake. The fault divides with one portion following the Miami 

 river valley and the other the long, narrow southern extension of 

 Indian lake, the Mossy Vly brook valley, and thence along the 

 western side of Piseco lake on the Piseco Lake sheet, the southern 

 portion of this line of fracture having already been described by the 

 writer in his report on the Lake Pleasant quadrangle. 



From these statements it will be seen that there is a prominent 

 line of fracture, with decided topographic influence, extending from 

 Piseco lake northeastward to near Lake Harris on the Newcomb 

 sheet, or a distance of some 45 or 50 miles. This Indian Lake fault, 

 therefore, ranks as the longest continuous line of fracture yet 

 located in the Adirondack region. This fault is also the only one 

 touching the Blue Mountain quadrangle which gives quite certain 

 evidence regarding the relation of upthrow and downthrow sides. 

 The upthrow side is clearly on the west with the amount of dis- 

 placement ranging up to 1000 feet or more, as, for example, on the 

 Indian Lake sheet. On the Blue Mountain and Newcomb sheets 

 the amount of displacement is much less. In the vicinity of Indian 

 Lake village the fault has no conspicuous topographic influence 

 because the soft Grenville limestone has there readily been worn 

 down on both sides of the line of fracture. 



The generally much greater altitudes on the west side, even in 

 homogeneous igneous rock, shows that important movements have 

 taken place along this fault since the development of the Cretaceous 

 peneplain. Hence this fault is in most respects very similar to 

 many of the prominent ones of the eastern and southeastern 

 Adirondacks. 



Other faults. The fault along Cedar river east of Pine lake 

 strikes north 40° east and shows excellent crushed zones but it can 

 not be traced far. On Cedar river, one-half of a mile above the 

 mouth of Rock river, a beautifully developed crushed-rock zone 50 

 to 75 feet wide is exhibited in the bed and in one wall of the river 

 channel and it can be traced several hundred yards. Absence of 

 any notable topographic influence, except the local determination of 

 the river channel here, suggests that the principal movements along 

 this fault must have antedated the Cretaceous peneplain. 



Another Hne of fracture extends foe 2 or 3 miles from the Cedar 

 river valley into the eastern end of the deep valley just south of 

 Blue ridge in the southeastern part of the quadrangle. Crushed- 

 rock zones are well developed with strike north 70° east along the 



