Washington — Charnockite Series of Igneous Rocks. 335 



Adirondacks.* The relations of the first are uncertain as the 

 description of the district is incomplete. While having some 

 features in common, the Canadian and Adirondack areas seem 

 to be of a somewhat different character, as augite very largely 

 replaces hypersthene, in Canada the masses are predominantly 

 of anorthosite, and in the Adirondacks angite syenite and 

 similar rocks are common. 



It is possible that a district similar to that of India exists in 

 the interior of the State of Bahia, Brazil. 



The mineralogical characters which the Norway, Ellesmere 

 Land, Cortlandt, and Ivory Coast regions have in common with 

 that of India are as follows : Hypersthene is the most important 

 and most characteristic mafic mineral in all the districts, and, 

 especially, is the essential mafic mineral in the most silicic types, 

 the granites, quartz monzonites, and quartz diorites. The pecu- 

 liar pleochroism of this hypersthene seems to be very constant: 

 a and b being in light red or pink tones (not the ordinary browns 

 or yellows), and c very pale green or blue gray. The parting 

 or cleavage parallel to 5(010) seems to be commonly developed, 

 rather than the normal prismatic cleavage, and schiller inclu- 

 sions are common. 



A " hypersthene-like " pyroxene with very similar pleo- 

 chroism and low birefringence has been described by J. J. 

 Allanf as occurring in the jacupirangite of the Ice River area 

 in British Columbia. It has an oblique extinction of about 

 38°, and is considered by him to be a clinohypersthene. It is, 

 however, optically positive, and the analysis, with its low SiO„, 

 considerable A1 2 3 , and high CaO and Ti0 2 , indicates that it is 

 really an augite, and that probably the marked pleochroism is 

 due to the presence of the titanium. 



A colorless or almost colorless mouoclinic augite, with a 

 faint pleochroism similar to that of the hypersthene, is some- 

 times present, but generally in very small amount. In Norway 

 it seems to be more common. This is generally wanting in 

 the more silicic types. Hornblende begins to appear as silica 

 falls, and is abundant (though less so than the hypersthene), 

 in the most femic types. It is constantly of a brownish-green 

 color, and highly pleochroic in tones of yellow brown and 

 yellow green. Biotite is rare or accessory and quite absent in 

 most of the t} 7 pes. 



A soda-lime feldspar is present in all except the most femic 

 types, such as the pyroxenites.ij; It varies in composition from 

 an oligoclase in the granites to a labradorite in the norites. In 



*Cf. H. P. Gushing, various papers in A. E. N. Y. St. Mus. and B. G. 

 Soc. Am. 



+ J. J. Allan, Can. Geol. Surv., Mem. 55, p. 169, 1914. 



\ In these the normative feldspathic molecules have entered the modal 

 hornblende. 



