ROGERS, GEOLOGY OF THE CORTLANDT SERIES 33 



inclusions are oriented with respect to this. These inclusions are prac- 

 tically always visible with the high power objective, and they often be- 

 come very large. They are usually reddish and are seldom opaque, al- 

 though when abundant they may almost obscure the pleochroism of the 

 mineral. By reflected light, they exhibit an excellent metallic luster, 

 resembling that of phosphor-bronze. They are in many cases recti-tri- 

 angular in shape, but sometimes four-sided and often irregular. Altera- 

 tion of the hypersthene is fairly common, usually to bastite, which is 

 then geometrically oriented on the altered pyroxene. Alteration may 

 begin at the ends, or the bastite may be flecked over the surface of the 

 crystal. Its color is yellowish green, and it practically lacks pleochroism. 

 Uralite may occasionally form on the hypersthene ; it is distinguished 

 from the bastite by its pleochroism, deeper color and more fibrous habit. 



The opaque mineral in these rocks is chiefly ilmenite, in large irregular 

 masses, magnetite being usually markedly subordinate. Pyrite is not 

 uncommon, but pyrrhotite is rare. Apatite occurs in all quantities, 

 usually in small, well defined rods, but sometimes in large crystals, sev- 

 eral millimeters long. The crystals show a sharp hexagonal outline in 

 cross section, with frequently a member of fine parallel rod-like inclu- 

 sions — so fine in fact that they resemble the parting which is sometimes 

 developed in corundum parallel (1011). The figure is the same in the 

 two minerals, and the relief and birefringence seem to be higher in these 

 apatites than usual. In one rook in which the identity of the mineral 

 was doubtful, a test for phosphoric anhydride was made, but the high 

 percentage (2.45) removed all suspicion of its being corundum. This 

 latter mineral was not noticed in any of the normal igneous rocks of the 

 series. 



In several slides, hornblende (usually light brown) was present in sub- 

 ordinate quantity, marking a passage to the biotite hornblende norites. 

 Augite may also enter, to indicate the transitional phase to the biotite 

 augite norites, but biotite norite appears to be a fairly constant type. 



Biotite Augite Norite (Hyperite) 



Biotite augite norite is the most important of all the norites, and from 

 its central position it gives the impression of being the fundamental 

 norite magma. There are three large areas, two of which are probably 

 connected as mapped; two smaller ones, one on the west border and the 

 other on the eastern, and a third located in the pyroxenite area. It also 

 frequently occurs in the complex on Montrose Point, associated chiefly 

 with the pyroxenites. Williams's specimens are taken mostly from this 



