GENERAL GEOLOGY 23 
pleochroism in brown and green. The plagioclase is 
zonal and is a complexly doubly-twinned labradorite. 
A compact, fine-grained, dark, normal kersantite, with 
biotite as the only colored constituent, cuts the granite near 
Glacier Station. Another dike (38), of a normal diabase 
full of calcite spots, occurs at the same station, and a third 
dike of diabase (51), a foot wide, at the Summit Station. 
YAKUTAT BAY 
In Yakutat Bay most of the rocks seen in situ belong to 
the Vancouver or Yakutat Series, described in another 
chapter. Mr. Gilbert in crossing the moraine of the great 
Hubbard Glacier at the head of the bay, found among its 
boulders, besides the very abundant black slate and sand¬ 
stone of the Yakutat series, a variety of crystalline rocks 
probably brought down by the glacier from the higher 
peaks of the St. Elias chain. As little is known of the 
nature of the rocks constituting this crystalline axis, it 
seems worth while to catalogue these rocks. 
Glaucophane-quartz-schist (188). A bluish to greenish, compact 
rock with several parallel white quartz veins traversing the specimen. 
Under the microscope the fine granular quartz of which the rock chiefly 
consists is seen to be full of needles of strongly pleochroic glaucophane, 
which gives the rock its prevailing blue color, and of grains of epidote 
which are in places sufficiently abundant to color the rock greenish. A 
somewhat similar quartzite was found in boulders in the moraine of 
Hidden Glacier. 
Amphibolite (190). A very massive, coarse, granular rock, consist¬ 
ing principally of green fibrous hornblende with small amounts of 
interstitial plagioclase and quartz. Possibly a basic segregation in a 
massive diorite. 
Hornblende-gneiss (192). Blackish contorted gneiss, made up of 
dark needles of hornblende and plagioclase grains. Considerable 
rutile in twinned crystals, and a little quartz. 
Epidote-quartz-schist (194). A mottled and banded greenish and 
white rock consisting chiefly of granular quartz with relatively large 
