64 NEW YORK STATE MUSEUM 



Catamount. Fully fourteen kinds of rocks are represented, most of 

 them having been formed at different times. Oldest of all are the 

 Grenville hornblende gneiss and crystalline limestone well shown 

 in, and just west of, the quarry at the base of the mountain. In 

 contact with this Grenville gneiss there are good outcrops of 

 typical Whiteface anorthosite. On the southeastern slope of the 

 mountain, syenite grades into granitic syenite, and this, in turn, 

 into coarse granite. A narrow band of Keene gneiss, formed by 

 assimilation of anorthosite by the granite magma, lies between the 

 granite and anorthosite near the southern base of the mountain. 

 Numerous small aplite dikes cut the granite parallel to the foliation 

 toward the top of the mountain. In the vicinity of the aplite 

 dikes, quartz veins lie across the foliation of the granite. Dikes of 

 gabbro-diorite cut the granite roughly parallel to its foliation at and 

 near the summit, and one-half of a mile to the northeast. A small 

 stock of typical gabbro cuts anorthosite, Keene gneiss and granite 

 near the base of the mountain. A diabase dike 6 feet wide sharply 

 cuts the granite just, south of the summit. A diabase dike and a 

 small pegmatite dike cut obliquely across the larger of the gabbro- 

 diorite dikes one-half of a mile northeast of the summit. Glacial 

 deposits are extensively developed around the foot of the mountain. 



STRUCTURAL GEOLOGY 

 Tilting and Folding of the Grenville Series 



It has been generally assumed that the Adirondack Grenville 

 strata have been severely compressed and folded as well as thor- 

 oughly metamorphosed and foliated by the compression. Recently, 

 however, the writer has presented strong evidence^ that the Gren- 

 ville strata have neither been highly folded nor severely com- 

 pressed, while many broad belts of Grenville are known to be prac- 

 tically undisturbed or only very moderately folded, and many 

 masses, large and small, are merely tilted or domed at various 

 angles. Very locally the strata are sometimes contorted. Paral- 

 lelism of Grenville and syenite-granite rock belts is common with a 

 general tendency toward northeast-southwest strike, but there are 

 so many notable exceptions (some, for example, in the Lake Placid 

 quadrangle) that any generalization, regarding such a strike of the 

 rock belts as due to severe lateral compression, is of little signifi- 

 cance. 



1 Jour. Geol., 24:588-96. 1916. 



