34 ANNALS NEW YORE ACADEMY OF SCIENCES 



locality, although he mentions the western portions of both of the other 

 areas. 



This rock closely resembles the biotite norites, being medium grained 

 and either dark pink or dark gray. One or two light pink specimens 

 have been taken, but this variety is uncommon. The rock seldom shows 

 any metamorphism. 



The feldspar is identical with that in the biotite norites, the orthoclase 

 being present in about the same quantity. The plagioclase is usually 

 andesine, but in one of the light pink specimens mentioned above, it was 

 oligoclase, and when the rock is dark gray it may be labradorite. ' The 

 hypersthene and biotite occur as described under biotite norite. Green 

 augite is the other essential mineral in this rock, and it appears to be 

 closely related to the hypersthene. In shape, the crystals resemble each 

 other strongly, and the augite often carries inclusions identical with those 

 occurring in the hypersthene. These are clustered in the center of the 

 crystal and are often so abundant as to render it dark reddish brown, but 

 the margin usually is free and retains its clear green color. The color 

 is about that of the Z ray of the orthorhombic variety. In many cases, 

 an intimate intergrowth of augite and hypersthene was observed, a patch 

 of pleochroic hypersthene appearing in an augite crystal, with the cleav- 

 age and inclusions coincident. The augite may, of course, be distin- 

 guished by its lack of pleochroism, its extinction angles of 40° -50°, its 

 higher birefringence and its interference figure in basal section. Both 

 simple and polysynthetic twinning were occasionally noticed in the same 

 region, although these are both more common in the pyroxenites. Altera- 

 tion is similar to that of the hypersthene, except that chlorite and horn- 

 blende are the common products. 



The ferromagnesian minerals constitute in typical specimens from 

 one-third to one-half the rock, but their mutual proportions vary consid- 

 erably. The hypersthene makes up usually about one-half, with the bio- 

 tite and augite in subequal amounts; frequently, however, these will ex- 

 ceed the hypersthene in quantity. Original hornblende is rather rare. 



The apatite may become very abundant in this rock; in one case, the 

 little rods were so plentiful in the orthoclase as to constitute one-third 

 or more of its bulk. Ilmenite is much more abundant than magnetite, 

 and pyrite and pyrrhotite are not uncommon. 



The order of crystallization of the ferromagnesian minerals is some- 

 times hypersthene, augite and biotite, and sometimes hypersthene and 

 augite, and then biotite The orthoclase usually cn r stallizes last of all. 



Williams does not recognize this member as a distinct variety ; he groups 

 all of the augite norites together. That the subdivision is a rational one, 



