GEOLOGY OF THE LAKE PLACID QUADRANGLE 57 



crushed rocks are notably granulated, and in thin section the 

 crushed granite shows very interesting examples of sliced and 

 granulated quartz (see plate 12). 



Gabbro-diorite Dikes 



These very interesting dikes show considerable variation in 

 mineralogical composition, but all of them may be classed as ortho- 

 clase gabbro-diorites. No rocks of this sort have ever been 

 observed by the writer elsewhere in the Adirondack region. Alto- 

 gether ten or twelve dikes were found, eight or nine on Catamount 

 mountain, and two on the mountain i^ miles north-northeast of 

 East Kilns. These dikes are certainly younger than the coarse 

 granite of the syenite-granite series, and older than the diabase, 

 and some, at least, of the pegmatite, dikes. Whether they are older 

 or younger than the gabbro stocks could not be determined. 



Five or six of these dikes at or near the summit of Catamount 

 very clearly cut the great bare ledges of granite for distances up to 

 one-fourth of a mile. They vary in width from 2 to 30 feet, those 

 toward the very summit all being over 20 feet wide. The strike of 

 the dikes is roughly parallel to the foliation of the granite but it 

 varies from N io° E to N 50° E, the latter being the strike of the 

 large dike which lies just below the summit and reaches one-fourth 

 of the way down the mountain. The dikes are badly weathered 

 (much more so than the granite) to brownish gray, so it is impos- 

 sible to obtain good specimens of fresh rock. Contacts against the 

 granite are rather sharp, and the dikes stand in practically vertical 

 position. Two wide dikes just below the summit are weathered 

 and eroded out leaving clear-cut trenches in the granite, these 

 trenches being visible from the base of the mountain. All the rock 

 is somewhat gneissoid, but the larger dikes are usually clearly finer 

 grained and more gneissoid to almost schistoid at the borders. The 

 most common facies of the dike rock is fine to medium even grained 

 with mineralogical composition shown by no. 57 of table 4. Another 

 facies is almost medium, even grained, and looks something like a 

 basic phase of the syenite. Its mineral content is given as no. 56 

 of table 4. Least common is a fine-grained facies with scattering 

 flakes of biotite each several millimeters across. Its mineral con- 

 tent is shown by no. 59 of table 4. As already stated, it was not 

 positively determined whether the small aplite dikes in the immedi- 



