INTRUSIVE ROCKS OF THE DISTRICT OF MONTREAL. 433 
triclinie feldspars. The associated crystals of hornblende are always 
much smaller and less distinct, forming with grains of feldspar a — 
matrix to which the larger feldspar crystals give a porphyritic aspect. 
Finer grained bands, im which magnetite and ilmenite predominate, 
traverse the coarser portions, often reticulating ; while the whole mass 
is also occasionally cut by dykes of a whitish or brownish-gray 
trachytic rock, which is often porphyritic. If, as is not improbable, 
these dykes belong to the great trachytie portion of the mountain, it 
would show that here as m Mount Royal, the trachytes are more 
recent than the dolerites or diorites, but the relations of these different 
rock have yet to be made out. 
A portion of the coarse grained diorite selected for examin- 
ation, contamed besides the minerals already enumerated, small 
portions of black mica, with grains of pyrites, and alittle dessemi- 
nated carbonate of lime, which caused the mass to effervesce slightly 
with nitric acid. ‘Fhe macled feldspar crystals, sometimes half an 
inch in length and beautifully striated, were so much penetrated by 
hornblende that they were not fit for analysis, but by crushing and 
washing the rock a portion of the feldspar was obtained which did not 
effervesce with nitric acid, and contained no visible impurity except a 
few seales of mica. The specific gravity of the powdered feldspar was 
2.756—2.763. It was attacked by hydrochloric acid with separation 
of pulverulent silica, but the complete analysis by this means was 
somewhat difficult, a portion of the mineral escaping decomposition, 
so that the ordinary method of fusion with an alkaline carbonate 
waa had recourse to. Two analyses gave as follows :— 
VIL. VIII. B. 
PSTIPCHPT HTN oiak. sibs die ohotelaselers 46.90 47.00 45.40 
PRUETT eyes Ee ea Pee 31.10 } 32.65 30.45 
eroxy Qin mtOny, 1 ie biel 1.35 80 
PUA G 5 ep seeve yo Avea Mista aii ie caplet 16.07 15.90 14,24 
METERS Ob bel Ce OMee es CTE eRe 65 suchas 87 
Rotashwiesswrtaie hc abst ofapata me .58 siabess 38 
SO a Soe aos ae parciaa isk chat pa latara to ae raed Sorc 2.82 
VG ETH Rate ROE AGB See eae 1.00 Sate 2.00 
99.49 98.96 
This feldspar then approaches closely in composition to anorthite, 
which although formerly regarded asa rare species, has recently 
been shown by Deville, Damour and Forchammer to enter into the 
