T. S. Hunt on Lithology. 177 
magnesia 33°50, protoxyd of iron 26°20, alumina 3:00=1 ; 
being equal to 18°4 of magnesia for the entire mass. In another 
experiment, 18:0 per cent were obtained. Taking the mean of 
the two analyses of olivine above referred to, which gives 39°5 
per cent of magnesia, 18-0 parts of this base correspon 
parts of olivine. The remaining 9°5 parts of dissolved matter 
represent alumina and silica from the feldspar, and oxyd of iron 
from the magnetite; both of which were somewhat attacked by 
the acids. The undissolved portion of the rock equalled 44-7 
per cent, and appeared to consist of a feldspar with pyroxene, 
some mica, and a little magnetite. Its analysis afforded silica 
49°35, alumina 18°92, protoxyd of iron 451, lime 18°36, magne- 
sia, 6°36, loss (alkalies ?) 2°50=100-00. 
_ In some portions of the dolerite of Montarville the feldspar 
18 more abundant, and appears in slender crystals with augite, 
and with a smaller proportion of olivine than the last. A speci- . 
men of this variety being crushed and washed gave 3-9 per cent 
of magnetite, and 10:0 per cent of a mixture of ilmenite with 
olivine. The feldspar was obtained nearly pure, in yellowish 
Vitreous grains, having a specific gravity of 2°73—2°74, and 
nearly the composition of labradorite. The results of its analy- 
SiS are seen under XVIII. ry 
whole were dissolved. This portion consisted of silica 87°30, 
00-00; 
XVIII. xix. 
leg SS ee SG 5360 
Adetating 861° Fg BAG AEE CR 960g 24°40 
Peroxyd of incon, 08 > ee a ; 
* Taran genres Sect eee Se 8-62 
me ay : ee, si snide 
sean idice bemcae aoe. ae Cie “ 
Volatile, - aes ad -60 -80 
99°00 
The dolerite of Montarville is traversed by veins belon ing 
Several different periods. In one instance, the black and hig 
Rougemont.—The rocks of Rougemont offer a general resem- 
blance to those of Montarville. Some portions are a coarse- 
Stained dolerite, in which augite greatly predominates, with 
Sead of feldspar, and a little disseminated carbonate of lime. 
4n some parts, the augite crystals are an inch or more in diam- 
ter, with brilliant cleavages; and grains of pyrites are abun- 
dant, with calcite in the interstices. This rock resembles the 
Y augitic dolerite of Montarville. Olivine is very abun- 
dant in two varieties of dolerite from Rougemont. One of these 
1964, 
420, Jour. Scr.—Szconp Sexms, Vor. XXXVIII, No. 113.—Szrt., 
23 
