INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 439 
In Sir Willam Logan’s notes upon this mountain it is remarked 
that dykes of a fine grained granitic trap cut the augitic mass; and 
I find among the collections from this locality specimens of a light 
gray rock which is made up of a white crystalline feldspar with 
small prisms of black hornblende and scales of brown mica, resem- 
bling somewhat the finer grained diorite of Mount Johnson, while 
others more micaceous approach to that of Beleil. 
Mount Royal or Montreal Mountain.—A large portion of this 
mountain consists of a dolerite in which augite greatly predominates, 
resembling the highly augitic varieties of Rougemont and Montar- 
ville. The white crystalline feldspar, which is often very sparsely 
disseminated, is at other times more abundant, and occasionally 
predominates in bands, which traverse the dark coloured rock and 
appear to be veins of segregation. At the east end of the mountain 
a variety of dolerite containing olivine occurs ; it consists of a base 
of grayish-white granular feldspar, which constitutes in the specimen 
before me about one-half the mass, and incloses crystals of a brilliant 
black augite, and: others of semi-transparent amber-yellow olivine. 
This rock closely resembles the feldspathic olivine rock of Rougemont 
described above, but the imbedded crystals are somewhat larger, 
although much smaller than the crystals of the same mineral in the 
dolerite of Montarville. A portion of the feldspar freed as much 
as possible from augite, gave by analysis the following result, which 
shows that it approaches labradorite in composition : 
XVITI 
ST emery eRe ay Lisis atatat oti siebatelavyevovoteiehelersueretouelaie tetas 53°60 
PP ONORUINIA, ory Rioinie (dv ie vials la «eine elsivie else» afajele/e'a/s/e site en 2b 40 
Peroxyd Of ifON,. 06. se. cee eee eee eee cere cease 4°60 
TALON te] jhe rvebekalsy ake ele © shsiaievele eit slaves, sieve) ety 8°62 
Magnesia,..... sate ho AGC OOOH Be ROOAGe Ui coDUb OOH o 86 
AlKalies, by difference,. .. <0... 2 es accscres-ssscccns 6°12 
MViolabilestepartaca seetstats ote re ctelcverels wlereie\ sic cvs eles eve/elciclerale "80 
100-00 
The Silica contained 1:60 of matter insoluble in carbonate of soda, 
apparently titanic acid from intermingled ilmenite, from whence a 
portion of the oxyd of iron is also derived. 
Rigaud Mountain.—This, the most western of the series of intru- 
‘sive masses under consideration, is in great part made up of a rock 
which approaches in character those of Brome and Shefford, being 
