430 INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 
blende, which are sometimes associated. The proportion of these 
two minerals to the mass is never above a few hundredths and often 
less than one-hundredth. The other minerals are small brilliant 
crystals of yellowish sphene and others of magnetic iron, amounting 
together probably to one-thousandth of the mass; in some finer 
graimed varieties rare crystals of sodalite and nepheline are met with. 
These rocks never contain quartz, but being made up entirely of 
cleavable grains of feldspar without any cementing material, are very 
friable and subject to disintegration ; so that for some distance around 
the mountains, the soil is almost entirely made up of the disaggrega- 
ted crystals of feldspar, which however show but little tendency to 
decomposition, and retain their lustre. The rock is sometimes rather 
finely granular, but is often composed of cleavable forms, which are 
from one-fifth to one-half of an inch in breadth and sometimes nearly 
an inch in length. The cleavages of the feldspar are those of ortho- 
clase. The lustre is vitreous and in the more opaque varieties pearly, 
but the crystals never exhibit that eminently glassy lustre nor the 
fissured appearance which characterises the feldspar of many foreign 
trachytes, identical with these in composition. The colour of the 
feldspars of these mountains is white, passing to reddish on the one 
hand, and to pearl or lavender-gray on the other. 
Specimens of the rock of Brome Mountain were taken from the 
side near the village of West Shefford ; it was coarsely crystalline, 
lavender-grey in colour, and contained a little brown mica, sphene and 
magnetic iron, but no hornblende. The density of fragments of the 
mass was found to be 2:632—2°638. Selected grains of the feldspar 
had the specific gravity of 2°575 and did not yield anything to the 
action of hydrochloric acid. The analysis was effected in the usual 
way by fusing with an alkaline carbonate. The alkalies were deter- 
mined fromZanother portion, which was decomposed by ignition with 
a mixture of carbonate of lime and muriate of ammonia. The 
analyses of two portions from different specimens gave as follows: 
II ITI. 
Silicaygeagyes oi. 8 Pica HIG Fist ESO RCE ees 65°70 65°30 
ATU MMAR OA chore Gaal MeVersvens siofeie Go ckebntere 20°80 20°70 
BU eK Ss a ae atetiiacete COC COO aS ea oo *84 84. 
Potash,....... aitoietsaeiists alsvelereiate!cveistshereysisvere 6°48 
Soday vse cae: Ayal cialertve.s shelstevarernie Sere 6°52 
Volatile,........2..00 stocentate tet eee eiterets 50 
