178 T. S. Hunt on Lithology. 
has a grayish-white finely granular feldspathic base, in which 
are disseminated black augite and amber-colored olivine, the lat- 
ter sometimes in distinct crystals. The proportions of these ele- 
ments sometimes vary in the same specimen, the feldspar forming 
more than half the mass in one part, while in another the au- 
gite and olivine predominate. By the action of the weather, 
the feldspar acquires an opaque white surface, upon which the 
black shining augite and the rusty-red decomposing olivine 
appear in strong contrast. 
The dolerite of this mountain is traversed by numerous dikes, 
some of which are diorites like those of Monnoir and Beleil 
about to be described. A dike of compact dolerite, holding 
crystals of feldspar and grains of olivine is found intersecting 
the strata of the Hudson River formation at St. Hyacinthe. 
Mount Royai—tThis hill, which rises immediately in the rear 
of Montreal, consists for the most part of a mass of highly augi- 
tic dolerite. In some parts large crystals of augite, like those of 
Montarville, are disseminated through a fine-grained base, which 
is dark ash-gray in color, and often effervesces freely with acids 
from the presence of a portion of intermingled carbonate of lime. 
At other times this is wanting, and the rock is a mass of black 
crystalline augite, constituting a veritable pyroxenite, from which - 
imen examined constitutes about one half of the mass, 
and encloses crystals of brilliant black augite, and of semi-trans 
Se amber-yellow olivine. This rock closely resembles the 
ae peridotite of Rougemont, described above; but the 
imbedded ery 
in the dolerite of Montarville. A portion of the feldspar, , 
_ as much as possible from augite, furnished by analysis the result 
already given under xtx; which shows that it approaches labra 
dorite incomposition. => 
