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NEW YORK STATE MUSEUM 



rock upon the observer and this is due to the abundance of magnetite 

 grains and dark silicates. The minerals present are plagioclase, 

 green monoclinic augite, brown hornblende, hypersthene, garnet, 

 titaniferous magnetite and titanite. The more important ones of 

 these are shown in the accompanying figure (Fig. 2) which is a little 



Fig. 2.— Gabbro without reaction rims — near Ensign Pond, Moriah. F is labradorite; P, 

 augite; Hy, hypersthene; H, hornblende; Q, quartz; G, garnet; M, magnetite. 



richer in hornblende than the average. The rock is blotched with 

 light green from the altered feldspar, and has faint, pink streaks 

 running through it, due to the garnets. These latter give it a pecu- 

 liar reddish cast that is very characteristic. The feldspars are now 

 largely altered to saussuritic matter, but when not too far gone they 

 have a broad, lath-shaped outline, more or less idiomorphic, and are 

 rather coarsely twinned. At times they are filled with minute dots 

 or crystals of brightly polarizing character which are so small as not 

 to be easily recognized, but they are probably pyroxene. Less 

 commonly, polygonal scales of a brown color and in geometrical 

 arrangement are to be seen. These latter are generally regarded 

 when seen in other exposures as a micaceous variety of ilmenite. 

 The successive zones of grains of garnet and brown hornblende 

 between the dark silicates and the feldspar, or surrounding the 



