T. S. Hunt on Lithology. 261 
_ Among the intrusive rocks of Canada, to be described, are 
ech aiie compact, and earthy varieties of trachytic orthosites, 
ides trachytic porphyries. These rocks often contain dissemi- 
nated earthy carbonates, sometimes in considerable amount; as 
Deville had already shown for some of the trachytes of Hungary, 
the Rhine. Trachytes also hold in some eases disseminated por- 
tions of a zeolite, apparently natrolite, and through this mixture 
pass into phonolites, of which a characteristic variety will be no- 
ticed in this paper. Obsidian and pumice-stone, which are often 
associated with orthoclase trachytes, are related to them in com 
ition ; and pitchstone and perlite are similar rocks, differing 
owever in containing some combined water. Rocks resembling 
pitchstone, and sometimes porphyritie from the presence of dis« 
linet crystals of feldspar, occur in the south side of Michipicoten 
and, Lake Superior, but have not yet been examined. Ana 
ses by Jackson and by Whitney of the pitchstones of —oe 
diabase, The feldspar of diorites varies in composition from al- 
te to anorthite, and is occasionally accompanied by quartz. 
This, though most frequent with the more siliceous feldspars, is 
es of the Huronian series are in part at least diorites, 
inated hornblende, and it takes the name of greenstone. 
‘Aw. Jour. Sc—szconp Szrihs, VoL- raayu wee 110,—Manon, 1864, 
34 : 
