4352 INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 
just mentioned, apparently belongs to the same series. The mineral 
composition of these intrusive masses varies considerably, not only for 
the different mountains, but for different portions of the same 
mountain. 
Yamasha Mountain.—The greater portion of this mass is a grani- 
toid trachytic rock, which differs from that of Brome and Shefford in 
being somewhat more micaceous and more fissile. The dark brown 
mica is in elongated flakes, and hornblende is absent in the specimens 
collected, which however hold small portions of magnetite and minute 
crystals of amber-yellow sphene; these seem to be disseminated in 
veins of segregation, which are of a lighter colour than the mass.* 
The feldspar grains which make up this rock are brilliant, of a vitreous 
tustre, and often yellowish or reddish-gray in colour. Separated by 
washing from the crushed mass, the crystalline feldspar in powder had 
a density of 2°563, and gave by analysis as follows (V.) Another 
specimen of this granitoid trachyte, having been crushed and 
separated by a sieve from the greater portion of the mica, gave for the 
composition of picked grains (VI.): 
Vv. VI. 
SLC ar OMe eae wisrersahetets ie eerste scot ateisiers 61°10 58°60 
AVumina ee MOU Sah ss SEE pase ae 20°10 21°60 
ELON Y.GrOl ANOS ieysie) Melee cae afeyers, 2 efel=|eiale\ai™ 2:90 2°88 
MEG). ch stati dieses opentie POETS pha Oe con tase 3°65 5°40 
MIAGHESIAy «Het veto! ofall s: velohol tok clei ait siete orse cls 219 1°84 
WA GUASIN tera desta steartales dtat(a loved velar aanonsteed sal chal cls 8°54 3°08 
Soda eee eas Oe Orale ated gr arecel Reber ctaieravarite 5°93 5°61 
Wolatilesas er ons hiatal gaaie sora eee ets -40 *80 
98°41 eee i(il 
The south-eastern part of the mountain offers a composition entirely 
different from the last, being a diorite made up of a pearly white 
crystalline translucent feldspar, with black brilliant hornblende, 
ilmenite and magnetic iron. This rock is sometimes rather fine 
grained, though the elements are always very distinct to the naked 
eye, while in other portions large cleavage surfaces of feldspar half an 
inch in breadth are met with, which exhibit m a very beautiful 
manner the strie characteristic of the polysynthetic macles of the 
* For an examination of the sphene of the Yamaska Mountains see the Report for 1851, 
p. 119. By anerror of the press, the determined specific gravity is said to be 2°76 instead 
af 3:76, 
