436 INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 
Monéarville or Boucherville Mountain.—The collection of speci- 
mens from this intrusive mass off ers two orthree remarkable varieties 
of rock not met with in the mountains already described; and char- 
acterized by the presence of augite and olivine. The first variety 
consists almost entirely of coarsely crystalline black augite, with 
small scales of brown mica, and rare grains of white feldspar ; others 
of calcite are also scattered throughout the mass, and their removal 
by solution has left numerous little pits on the weathered surface ; 
it may be described as a highly augitic dolerite. Another and 
remarkable variety appears to form the greater part of the mountain ; 
it consists of olivine in rounded crystalline masses, from one-tenth 
to half an inch in diameter, associated with a white or greenish-white 
crystalline feldspar, black augite and a little brown mica and mag- 
netic iron. The augite appears both in the form vf small grains, 
and of well defined crystals, often an inch in length by half an inch 
in diameter, and partially coated with a film of brown mica; the 
olivine is evidently the predominant mineral. 
An average specimen of this olivinitic dolerite was reduced to 
powder ; it did not effervesce with nitric acid, and when ignited lost 
only 0.5 per cent. When heated with sulphuric acid the olivine was 
readily decomposed with a separation of silica, and by the subsequent 
use of a dilute solution of soda, followed by hydrochloric acid, and 
a second treatment with the alkaline ley, 55.0 per cent. of the mass 
were dissolved. The dissolved portion consisted of, 
XII 
SINT ae GR ernoae Hie SOMOS ap Del Ge NaaICr o 37.30 
IMAP EST areuyeie sc) treievewe ore op yelel iclapeieta shave ovetalstacerete creer 33.50 
ETOUOKY OL [OW -1.1-jajels «/0iet dieperacetene sic) si iat ade staleheieys ekets 26.20 
PAT UNIAN tener otleia et alel eel vel rausretde were conte ec tetetetoters 3.00 
100.00 
Another portion of the same pulverized specimen was gently 
warmed with dilute sulphuric acid, and the silica being removed from 
the residue by a solution of soda, some grains of olivine which still 
remained, were decomposed by a repetition of the process. The 
undissolved portion equalled 44-7 per cent., and appeared to consist 
of feldspar and pyroxene, with some mica and a little magnetite. 
The acid solution gave a quantity of magnesia equal to 18:0 per 
eent. of the rock. 
Selected grains of the olivine were now submitted to analysis. 
