6o NEW YORK STATE MUSEUM 



of the syenite were noted, the usual rock being the greenish 

 grey, quartzose variety so well known throughout the Adirondacks. 

 There are many fine exposures as, for example, on Blue mountain, 

 Owl's Head mountain and in the vicinity of Long Lake village, 

 particularly in the large stone quarry alongside the road i^ miles 

 southwest of the village. With increasing quartz content this rock 

 passes into a granitic syenite which frequently shows a pinkish 

 color. The granitic syenite in turn grades into true granite gneisses 

 which are nearly always pink or red. Many small and large Gren- 

 ville gneiss bands or inclusions occur parallel to the foliation in 

 all facies of the syenite-granite series. Frequently these rocks 

 show rather rapid changes in color and composition parallel to the 

 foliation, though not the slightest evidence that one of these rock 

 types cuts another has yet been found. Rather there is much 

 evidence to show that the different facies really grade into each 

 other and are only variations of the same intrusive body. Though 

 at times the porphyritic texture is somewhat developed, no map- 

 pable areas of granite or syenite porphyry were found. 



Mixed gneiss series. There are two considerable areas of syenite- 

 granite and Grenville mixed gneisses. One of these occupies several 

 square miles just south of Blue Mountain and Eagle lakes and the 

 other some 8 or lo square miles along the northern border of the 

 quadrangle. As usual, in areas previously reported by the writer, 

 these rocks consist of Grenville strata shot through by and closely 

 involved with syenite or granite. Often wide bands of Grenville are 

 plainly visible while more rarely the Grenville has been more or 

 less assimilated by the intruding magma. 



Gabhro. Several gabbro stocks or dikes of the usual sort with 

 associated amphibolite' have been found. The largest, occupying 

 three-fourths of a square mile, is crossed by the main road 4 miles 

 east of Long Lake village. 



Diabase. Two fine diabase dikes occur on the eastern shore of 

 Long lake, respectively one-half mile and i mile north of Long 

 Lake village. One dike has a width of 40 feet and both show sharp 

 contacts and clear-cut branches from the main masses. They strike 

 north 30° east. 



Faults. It is quite evident that the western portion of the Blue 

 Mountain quadrangle lies west of the region of extreme faulting 

 in the Adirondacks. Good evidence for but one fault was found 

 and this line of fracture has determined the Raquette river channel 

 across the corner of the quadrangle. Thus the remarkably straight 



