12 
MUSEUM BULLETIN NO. 2. 
& 0 * 
52-63 
Na 2 0 
1-41 
T 102 
0-62 
K 2 0 
2-29 
Ab03 
16-76 
H 2 0+ 
0-12 
F 62(13 
2-86 
H 2 O- 
1-17 
FeO 
10-74 
P 2 O 5 
0-33 
MnO 
0-38 
C0 2 
0-10 
MgO 
4-33 
CaO 
6-17 
99*91 
S.G 2-954 
In the quantitive classification, this rock falls in an unnamed 
sodipotassic subrang of bandase. 
Granite (. Micropegmatite ). The quartz diorite, with a decrease 
in hornblende and plagioclase and an increase in quartz and 
micropegmatite, gradually passes into granite (micropegmatite), 
which occurs at or near the upper contact of the sills; in the latter 
case closely resembling the distribution of the materials in the 
laccoliths of Shonkinsag and Square Butte 1 . The thickness of 
the granite (micropegmatite) bears no relation to the thickness 
of the sill, for cases will be cited below where sills 140 feet thick 
contain a large amount of granite (micropegmalite), while other 
sills, in the same section, 900 feet in thickness, are entirely 
basic. In the hand specimen the granite (micropegmatite) 
is a fine-grained, holocrystaliine to porphyritic rock of pinkish- 
grey colour, in which can be identified biotite, quartz, and 
feldspar. Under the microscope, are seen the essential con- 
stituents, quartz, biotite, and micropegmatite, with the accessory 
constituents, microperthite, and plagioclase — probably andesine 
(Plate I, fig. 2.) The rock is very quartzose, the quartz occurring 
in large irregular masses associated with micropegmatite, in 
which the quartz holds the orthoclase. The latter is filled 
with dust-like inclusions and is generally scattered evenly 
throughout the quartz in small, round masses which extinguish 
simultaneously. Again, the orthoclase is only seen in the 
peripheral parts of the quartz, while the centre is quite free 
from such inclusions. Plagioclase — andesine to labradorite — 
is present in small amounts. Biotite is very plentiful and 
J L. V. Pirsson, U. S. G. S. Bull. 237, p. 43. 
