CoriiJidum-Beat mg Rocks of Canada. — Miller. 2 8 1 
II. "Anorthit-Hornblendegestein vom Konschekowskoi Kamen im 
Ural, nach Roth's Rerechnung zu qo Anorthit, 10 Hornblende." Analy- 
sis quoted by F. Zirkel, Tschermak's Min. Mitt., 1871, page 62. 
III. Township of South Sherbrooke, Eastern Ontario. 
IV. Ottawa (formerly Bytown) on the eastern boundary of Ontario. 
This analysis is by T. Sterry Hunt, who thus describes the specimen 
examined "a greenish-white granular variety of anorthosite rock, from 
a boulder near Ottawa, having a density of 2.73. This is a portion of 
the specimen upon which Dr. Thompson founded the species named by 
him bytownite The rock is coarsely crystalline and made up of 
black hornblende, with a little sphene, and a white triclinic feldspar, 
the cleavage surfaces of which are sometimes half an inch broad, and 
beautifully striated." Geology of Canada, 1863, page Jq. 
Most writers state that labradorite is the essential consti- 
tuent of what they call the typical anorthosytes. It would 
seem that this is owing to the fact that few analyses have been 
made of these rocks. Moreover, it may be said that only com- 
paratively restricted areas have been examined. The most of 
Hunt's analyses and those of other workers on this continent 
were on samples froin the district in Quebec which lies adja- 
cent to the St. Lawrence river and from the adjoining region in 
the United States to the south. The assumption that labrado- 
rite is the typical feldspar of these rocks may moreover be due 
to the fact that most of the areas of anorthosyte, to which at- 
tention has been directed, are of large size, and thus, for va- 
rious reasons, would, on the whole, be more acidic in character 
than smaller outcrops. From the analyses which have been 
quoted by the present writer from Ontario and Russia, it 
would seem that no one plagioclase should be considered the 
typical constituent of these rocks. 
Rosenbusch* quotes four analyses of anorthosytes, Kempt 
three and Adamsl two. These range in percentage of silica 
from 53.42 to 59. 
A part of the .specimen from South Sherbrooke, the analy- 
sis of which has been given, was reduced to powder. The 
feldspar and hornblende were then carefully separated by 
means of a heavy solution and subjected to analysis. The feld- 
spar was found to have the composition .represented by the 
formula AbiAm. 
*Elemente der Gesteinslehre, pages 151 and 153. 
tHandbookof Rocks, page 49. 
JN. J. fiir Min. 1893, page 494. 
