INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 441 
In another specimen of this rock, also from Rougemont, and made 
up of thin layers of white crystalline red-weathering dolomite with 
others of a compact greenish-gray mineral, are interposed layers of 
blackish green crystalline hornblende from one-sixth to one-fourth 
of an inch in thickness; like the other bands they are variable in 
thickness and interrupted. Occasionally the cleavages of the horn- 
blende, which are nearly perpendicular to the beds, are seen cutting 
through thin layers of the dolomite, which as before, weathers 
reddish-brown. 
A portion of the rock free from hornblende was attacked with 
effervescence by warm dilute nitric acid, which dissolved 54.0 per ec. 
of carbonates of lime, magnesia and iron. The soluble portion had 
the following composition : | 
Carbonate of lime...... -opodoogo00Ne doseboaddardes 38.9 
i MIDAS CET A/C a) oh ce cinja\'eVejw o's) efehcl es sisie)aia/oe s\e'4 vanihro lee 
4 WON oon abooobcadueboanoogcoeddoou wds 29.9 
100.0 
Minute grains of pyrites were disseminated through the rock, 
which gave to the acid traces both of copper and nickel. The residue 
decomposed by fusion with carbonate of soda was found to contain— 
silica 65.40; alumina 10.10; lime 0.56; magnesia 2.05 ; protoxyd 
of iron 4.80; titanic acid 7.30; volatile 2.20; loss (alkalies ?) 7.59 
= 100.00. 
The fossiliferous limestones around the mountain of Montreal 
appear to have suffered very little change from the proximity of the 
igneous rocks. In one instance a portion of the limestone for the 
distance of five or six inches from the dolerite was seen to be whiten- 
ed, and intermixed with a portion of a greenish matter having 
somewhat the aspect of serpentine. Nitric acid dissolved from the 
crushed rock carbonate of lime with some alumina and a trace of 
magnesia, and the residue dried at 212° F., gave by analysis, silica 
40.20; alumina 9.30; protoxyd of iron 5.22; lime 36.40; magnesia 
3.70; volatile 0.20=95.02. The insoluble matter of these lime- 
stones is generally aluminous, and contains only traces of earthy 
protoxyd bases. A portion of the gray fossiliferous limestone from 
the vicinity of the mountain left by the action of a dilute acid a 
residue black with carbonaceous matter, which became white by igni- 
tion, and equalled 12:8 per cent. of the rock. It was an impalpable 
Vou. V. 2H 
