38 NEW YORK STATE MUSEUM 



gneisses two-thirds of a mile west of Long Lake bridge; a number 

 of small dikes cutting the anorthosite-gabbro west of Long lake; 

 and several small dikes cutting the large gabbro stock i^ miles 

 north-northeast of Indian Lake village. 



Veins of pure white quartz a few inches wide sometimes occur 

 in the syenite, granite or mixed gneisses and apparently always 

 parallel to the foliation. On top of Owl's Head mountain and also 

 two-thirds of a mile wxst of Long Lake bridge, sharply defined 

 pegmatite dikes a few inches wide were observed to cut such quartz 

 veins (see plate 10). Within the North Creek quadrangle the 

 writer has found diabase cutting pegmatite of the kind here 

 described. So far as the evidence goes, therefore, this type of 

 pegmatite is intermediate in age between the gabbro and the diabase. 



Graphite in pegmatite. A feature of particular interest in con- 

 nection with the pegmatites is the content of graphite in two small 

 dikes cutting Grenville limestone respectively one-half and three- 

 fifths of a mile northwest and north of the bridge across Cedar 

 river. In addition to some large flakes of graphite, these dikes 

 contain numerous balls or globular masses of graphite from i to 5 

 mm in diameter. They look exactly like tarnished lead shot. They 

 occur either as inclusions in feldspar or along contacts between 

 feldspar and quartz. When broken open these graphite balls are 

 seen to possess a perfectly developed radiated structure. 



Diabase Dikes 



Only two small diabase dikes were located within the quadrangle. 

 It is quite possible, if not probable, that others exist but wxre not 

 encountered in the rough and heavily glaciated region, though no 

 boulders were anywhere found which would lead to the suspicion 

 of the presence of other dikes. So far as the positive evidence 

 goes for this and the adjoining Long Lake quadrangle, diabase 

 dikes are notably smaller and rarer in the central than in the eastern 

 and southeastern Adirondacks. The finer grained, to sometimes 

 even glassy, texture of the diabase proves it to be the youngest of 

 the Adirondack intrusives. 



The larger dike cuts the anorthosite gabbro on the shore of Long 

 lake a little over a mile northeast of the bridge. The best exposures 

 are on the point already described as showing the most typical 

 anorthosite-gabbro. Here the dike is considerably branched but 

 shows a maximum width of 57 feet including two or three bands 

 or inclusions of the country rock. Sharp contacts against the 



