ROGERS, GEOLOGY OF THE CORTLAXDT SERIES 31 



structure of the feldspar. The globulites are extremely small and are 

 scattered promiscuously over the crystal, except at the border and on the 

 margins of the larger inclusions (i. e., the rods and plates, or crystals o£ 

 magnetite) ; and this clear margin moreover varies directly as the size of 

 the inclusion. This would indicate that they represent the form in 

 which the iron of the rock first crystallized, many of them combining 

 later to form the larger inclusions. The inclusions may be gray in color, 

 then imparting a dark gray color to the feldspar, and they may be so 

 plentiful that the mineral even in thin section is gray. They are de- 

 scribed here at some length, because this reddish dust is very character- 

 istic of the plagioclase in all of the norites and separates it sharply from 

 ihat in the gabbros, diorites, syenites and granites. The feldspar in this 

 rock is usually in a mosaic of small grains, the lamellae of the plagioclase 

 occasionally showing strain. The variety is usually andesine, as deter- 

 mined optically (angles 18°-20° on sections perpendicular to (010) and 

 hy specific gravity (2.674, according to Williams). The presence in con- 

 siderable amount of orthoclase is attested by the analysis and by specific 

 gravity determination, but the proportion varies greatly in different 

 specimens. Carlsbad twinning and zonal growth have been noticed. 



A description of the hypersthene had best be reserved, since in the pure 

 norite it is not altogether typical. The pleochroism is generally some- 

 what fainter than usual, being from pink to light green. The crystals 

 are usually small and arranged in clusters, and inclusions are few or 

 wanting altogether. Magnetite and ilmenite are usually present in 

 smaller amount than in the other norites. Apatite is fairly well devel- 

 oped. "Williams also mentions garnet and pleonaste in specimens collected 

 at an emery cutting, but these minerals are associates of the ore and are 

 usually not found elsewhere. A peculiar variety of this rock, in which 

 the hypersthene has a rather remarkable habit, is found only at the emery 

 mines and will be described below. 



Bio tit e Norite 



Biotite norite is one of the three more important members of the 

 norite family, covering perhaps three and one-quarter square miles. It 

 occurs in two large areas and at least three small ones. In the area back 

 of Montrose Point, a number of small emery pits have been opened. This 

 patch may possibly be connected with the larger one to the east of the 

 railroad. One of the other areas is in biotite augite norite in the south 

 central part of the district and the other in pyroxenite in the extreme 

 eastern end. It is thus always associated with the other norites, as stated 



