20 NEW YORK STATE MUSEUM 



is very light gray and more compact looking, the feldspar having 

 a dull instead of the usual shiny luster. In thin section (no. Ki6, 

 table 2) the feldspar and hornblende appear to be badly decomposed. 

 Possibly this facies is an effect of the heat of intrusion of the dia- 

 base dike. About 50 feet east of the dike the anorthosite-gabbro 

 has the same mineral composition (no. 64, table 2) but is con- 

 siderably weathered to brownish gray, shows very few, small, 

 uncrushed feldspar cores, and is moderately gneissoid. From 75 

 to 90 feet east of the dike the rock is weathered to a deep brown, 

 is clearly gneissoid and looks so much like a basic phase of the 

 syenite that, seen alone, it would scarcely be regarded as belonging 

 with anorthosite (no. 65, table 2). All the facies just described 

 grade perfectly from one into the other, but farther eastward, that 

 is beyond 100 feet from the dike, there are no exposures at the 

 base of the mountain so that the relation of the anorthosite to the 

 syenite of the mountain could not be determined. Along the lake 

 shore for one-quarter of a mile northward from the rocky point 

 just described there are ledges of gray anorthosite-gabbro. Then, 

 after a short interval, there is a ledge of what is taken to be a basic 

 (gabbroic) phase of the syenite (no. 55, table 4). A few rods 

 directly south of the rocky point there is a ledge of either gabbroic 

 anorthosite or a basis phase of syenite, probably the latter (no. 56, 

 table 4). Still farther south along the lake shore, there are out- 

 crops of basic facies of the syenite. Thus, although the evidence is 

 not conclusive, the anorthosite-gabbro appears to grade into a 

 basic phase of the syenite of the region. Similar gradations have 

 been quite definitely proved within the Long Lake quadrangle by 

 Gushing who suggests that "' the observed relations seem to point 

 to the conclusion that the change is due to actual digestion, by the 

 molten syenite, of material from the adjacent (anorthosite) 

 gabbro." ^ 



In the small anorthosite-gabbro area west of the lake, big out- 

 crops cover fully one-half of an acre. The rock is much like the 

 main bulk of the anorthosite-gabbro just described as occurring on 

 the eastern shore of the lake. Toward the interior the mass is 

 entirely devoid of foliation, is light gray, shows occasional 

 uncrushed, bluish-gray labradorite crystal cores up to one-half or 

 three-quarters of an inch across, and contains a considerable per- 

 centage of dark-colored minerals and some garnet. Otherwise much 

 of the rock is darker gray and moderately gneissoid to almost black 



IN. Y. State Mus. Bui. 115, p. 479- 1907- 



