GEOLOGY AND PALEONTOLOGY 
I 9 
side and grains of epidote and titanite. The hornblende 
is in prisms, slender and very sharply bounded, showing 
pinacoids and often terminal planes also. It often encloses 
feldspar grains. It is generally very fresh, but occasionally 
shows alteration to chlorite. The feldspar showing albite 
twinning was proved by extinction and refraction to be 
oligoclase. The untwinned feldspar seemed to be of the 
same species, rather than orthoclase, which might be ex¬ 
pected to occur in this rock. The diopside is frequently 
surrounded by chlorite, and has probably furnished most 
of that mineral, which is quite abundant in parts of the 
slides, and is the only decomposition product present. A 
slide cut across the contact with the granite (60) shows at 
the contact a band, 1 mm. wide, of apparently pure glass, 
and the spessartite quite uniformly grows coarser-grained 
away from the contact. 
The hot waters of the springs, which have a tempera¬ 
ture of about 150° F. and contain sulphur and carbonic 
acid, seem to rise through the granite, which is the near¬ 
est outcropping rock. 
Dr. Dali visited Biorka Island, off Sitka Harbor, and 
found it to consist of a light-colored biotite tonalite, per¬ 
haps a phase of the Hot Springs granite. It is cut by a 
single large dike of rhyolite, which shows a pronounced 
parting into small columns. The thin section of this rock 
(51 and 52) shows a well-characterized flow structure, 
with abundant development of coarse spherulites along 
the lines of flow and about small scattered phenocrysts of 
quartz, oligoclase, and Carlsbad twins of orthoclase, the 
remainder of the groundmass being microgranular. 
GLACIER BAY 
In Glacier Bay a light-colored quartz-diorite or tona¬ 
lite was found to be the principal rock on the west side, 
as already determined by Reid. 1 It is cut by innumerable 
1 Glacier Bay and Its Glaciers, 16th Ann. Rep. U. S. Geol. Survey, Part i 
p. 433- i 8 9 6 - 
