AN INVESTIGATION INTO 
isooo 
13000 
1000 
40 80 
FIG. 20. New Glasgow Anorthosite. Stress-strain curves. 
ESSEXITE, MOUNT JOHNSON, PROVINCE OF QUEBEC, CANADA^ 
This is a rather coarse grained essexite from a quarry on the slope of Mount 
Johnson, which is a typical butte arising from the Paleozoic plain to the 
south of the city of Montreal and forming one of the Monteregian Hills.* 
The rock is massive and uniform in character and dark gray in color, and 
is extensively used as a building stone and also for monuments. 
The iron-magnesia constituents are represented by a violet augite, a deep 
brown hornblende, and a biotite also very deep brown in color, the first men- 
tioned being the most abundant and all three being frequently intimately 
intergrown. The light-colored constituents are plagioclase and nepheline, 
the former being more abundant than the latter, which often occurs as inclu- 
sions in the feldspar. Although polysynthetic twinning is frequently seen 
in the feldspar, a considerable proportion of it is untwinned. A separation 
by Thoulet's solution, however, shows that the feldspar is all plagioclase, 
there being no orthoclase in the rock. Magnetite in the form of small 
grains and apatite in rather large, well-defined crystals are present in consid- 
erable amount as accessory constituents. The rock is perfectly fresh. The 
constituents of the rock, and more especially the feldspar, have a tendency 
*Adams, F. D. The Monteregian Hills, a Canadian Petrographical Province. 
Journal of Geology, April-May, 1903. 
