1 6 NEW YORK STATE MUSEUM 



Some interesting exposures occur in the small area i l / 2 miles 

 northwest of the summit of Hayes mountain. In the old stone 

 quarry the rock is greenish limestone containing serpentinized green 

 pyroxene and some graphite. This is associated with some horn- 

 blendic and quartzitic gneisses. Similar rocks outcrop on the west 

 bank of the stream, but there the pyroxene is less serpentinized. 

 Undoubtedly this mass of Grenville is a fairly large inclusion in 

 the granite which outcrops close by on all sides. 



In the Hewitt Pond brook area there are several good outcrops 

 of Grenville hornblende gneiss and hornblende-garnet gneiss. 



A conspicuous lenslike mappable inclusion of hornblendic and 

 quartzitic well-bedded gneisses occurs in the granite i% miles east- 

 southeast of Boreas river. 



Still other masses of Grenville occur within the quadrangle, but 

 these are so closely associated with other rocks that they are 

 mapped and described as " mixed rocks." 



Anorthosite Series 



General considerations. Recently the writer has published a 

 rather elaborate paper 1 on the whole problem of the age, relations, 

 and origin of the Adirondack anorthosite. The interested reader 

 is referred to that paper for much more material than is pre- 

 sented in this bulletin. Some years ago, Professor Gushing, in 

 his report 2 on the Geology of the Long Lake Quadrangle, presented 

 evidence to show that the anorthosite is a great'intrusive body dis- 

 tinctly younger than the great syenite-granite series of the Adiron- 

 dacks. The writer heartily agrees with this view, and in his own 

 field studies, particularly in the Lake Placid and Schroon Lake 

 quadrangles, he has found much more evidence in support of Gush- 

 ing's view. Recently, however, Dr N. L. Bowen 3 has offered quite 

 a different explanation of the origin and relations of the anor- 

 thosite. His hypothesis and the writer's objections to it are briefly 

 stated below, but a fuller criticism is presented in the paper above 

 cited. 



The anorthosite occupies a largely unbroken area of about 1200 

 square miles of the central-eastern Adirondack region. It is promi- 

 nently developed with nearly all its facies in the Schroon Lake 



1 Geol. Soc. Amer. Bui. 29 No. 4, 1918, p. 399-462. 

 a N Y. State Mus. Bui 115, p. 479-82. 1907. 

 'Jour. Geol., 25:209-43. 1917. 



