20 NEW YORK STATE MUSEUM 



In the eastern portion of the Sand Pond mountain area the rock 

 is nearly white and free from femic minerals, nonfoliated, and 

 with only a few scattering blue labradorites (no. 21 of table i). 

 The rock of the western portion of the area strongly suggests 

 Marcy anorthosite and grades into it. It is light gray and non- 

 foliated with 10 to 20 per cent dark minerals and garnets and many 

 blue labradorites. 



The Severance-Smith hill area, the largest shown on the map, 

 comprises mostly rather uniform, very typical, Whiteface anortho- 

 site (nos. 17 and 19 of table i). At the extreme southern end it 

 contains an admixture of Grenville. 



In the large area southwest of Bailey hill the Whiteface anor- 

 thosite is mostly very typical. By the old road on the west side 

 there are some rather gabbroid, garnetiferous, foliated zones, and 

 in the eastern portion there are locally developed masses with many 

 garnets and some scattering blue labradorites. 



A large ledge of Whiteface anorthosite at Loch Muller is exceed- 

 ingly variable as regards both content of femic minerals and folia- 

 tion. It contains some bluish labradorites and scattering garnets 

 (no. 15, table i). One- third of a mile farther west in the same 

 area the rock is distinctly gabbroid and foliated and. carries 8 

 or 10 per cent of quartz (no. 16, table i). In the western part of 

 the area the rock is very typical Whiteface anorthosite. 



The long, narrow area south of Hewitt road shows Whiteface 

 anorthosite varying from light-colored, moderately gneissoid to 

 dark-colored, gabbroid, very gneissoid facies. 



The rocks of the area west of Bigsby hill exhibit many local 

 variations from typical anorthosite to very gabbroid, gneissoid 

 anorthosite. In some ledges quartz is visible to the naked eye. 

 Nos. 13 and 14 of table i are from this area. 



A big ledge of gabbroid, very gneissoid Whiteface anorthosite 

 (no. II of table i) in the small area i^ miles a little west of 

 north of Irishtown is intimately associated with Grenville horn- 

 blende-garnet gneiss, the latter commonly occurring as distinct 

 strips or lenslike inclusions in the anorthosite. 



The remaining small areas of Whiteface anorthosite require no 

 special description here. 



Variable composition and structure of the anorthosite and its 

 significance. General statements. Contrary to Bowen's statement 

 that " anorthosites are made up almost exclusively of the single 

 mineral plagioclase,"' the writer's experience in the field has made 



