T. S. Hunt on Lithology. 179 
Diorires. 
mountain consists, as already described, of a micaceous granitoid 
trachyte; but the southeastern portion is entirely different, being 
adiorite made up of a 
Spar, with black brilliant hornblende, ilmenite, and magnetic 
Won. This rock is sometimes rather fine-grained, though the 
mate, traverse the coarser portions, often reticulating ; and the 
Whole mass is also occasionally cut by dikes of a whitish or 
brownish-gray trachytic rock; which are often porphyritic, 
and may perhaps be branches from the trachytic part of the 
mountain. 
' _ A portion of the coarse-grained diorite selected for examina- 
tion contained, besides the minerals already enumerated small 
~~ 
Which did not effervesce with nitric acid, and contained no vis- 
, in associated wi 
eens black hornblende containing some titanic acid, with a 
ittle mica and some quartz. (R. H. Scott, L. # and D. Philos. 
Magazine, [4], xv, 518.) : 
_.,-/onnoir.—Monnoir, or Mount Johnson, is composed of a dio- 
_ ‘Tite, which, in its general aspect, greatly resembles that of Ya- 
Maska just described, except that it is rather more feldspathic, 
The finer-grained varieties are grayish in color, and exhibit a 
be Ure of grains and small crystals of feldspar, with hornblende, 
brown mics and magnetite. Frequently, however, the rock is 
