38 ANNALS NEW YORK ACADEMY OF SCIENCES 



gory as the augite norite, both being derived by subordinate change from 

 a much more important variety. The rock, however, is important as the 

 connecting link between the norites and the diorites; it finds a further 

 transitional phase in some of the latter, which carry hypersthene or 

 enstatite. 



The rock is the customary dark gray and is of medium grain. The 

 feldspar usually constitutes two thirds or more of the rock. It is chiefly 

 labradorite, there being little unstriated feldspar present. The hypers- 

 thene is a little more abundant than either the biotite or the hornblende. 

 The latter mineral is of the brown variety. Apatite is generally abun- 

 dant, and ilmenite is present in the ordinary amount and habit. Magne- 

 tite and pyrite are not abundant. 



Olivine Augite Norite 



Olivine augite norite, which is the most basic of all the norites, has 

 been found in only one small area, half a mile south of Pleasantside. 

 It is situated on the border of the norite district, where it adjoins the 

 pyroxenites. No olivine was noticed in them at this point, although it 

 may be occasionally present. The rock is evidently a local basic segre- 

 gation of the biotite norite member. 



The feldspar constitutes about three fourths of the rock and is almost 

 entirely plagioclase, of the andesine-labradorite series. Of the dark 

 minerals, green augite is somewhat the most abundant; it is occasionally 

 intergrown with the hypersthene and always contains the olivine. The 

 latter may be in large masses, or again it occurs in small grains. It is 

 always strongly cracked, but it is less altered than would be expected. 

 What alteration there is has formed chiefly antigorite; there is little 

 separation of magnetite. This makes up about one fourth of the ferro- 

 magnesian minerals, and the hypersthene, which has begun to alter to 

 bastite, nearly one third. There is a little biotite, generally in small 

 flakes. Ilmenite, magnetite and apatite are not abundant. 



Hornblendite 



Hornblendite is not common, being known in four small areas only. 

 One is located at the northern end of Lake Meahach, another a mile 

 south of Montrose; these are both in the main diorite area, and there is 

 little question as to their derivation from the diorites by local segrega- 

 tion, due to loss of feldspar. The others are in the pyroxenite district, 

 located respectively about a mile east and half a mile west of Dickerson 

 Hill. The latter appears to be an altered pyroxenite, the hornblende 



