3 « 
ALASKA GEOLOGY 
having streaks of yellowish glass which shows a partial 
fibrous devitrification. The glass penetrates some of the 
large plagioclase phenocrysts in a most elaborate lobate 
network, and these are certainly autogenous. Other feld¬ 
spars are clear, zonal, and, like the normal feldspars of the 
andesites of the tuff bed, often fractured; they may be 
inclusions. Hornblendes, partly changed to calcite, and 
large shining biotites seem also to be original, and the rock 
may be called a biotite-hornblende-andesite . It is crowded 
with minute fragments of all the basalt and andesite types 
found in the lower bed through which it passed, and with 
many glassy types which were not identified from that bed. 
Above the point where landing was made was the ruin 
of a hut. In following a dry brook bed up past this hut a 
ledge was reached, composed of a peculiar hornblende- 
andesite that seemed to belong to the black bed above the 
light middle bed. It is a dark fine-grained rock with dis¬ 
tinct phenocrysts of feldspar. These are placed in a 
glassy groundmass, loaded with evenly distributed feld¬ 
spar microlites forked at the ends, and long minute blades 
apparently of hornblende, which have been uniformly so 
far resorbed that they are crusted over with magnetite 
crystals and hardly determinable. 
ST. LAWRENCE ISLAND 
We landed on a coarse shingle beach on the north side 
of the island, about fifteen miles from the east end. The 
beach there is at the outer edge of a flat tundra plain, and 
is distant from the high part of the island, which we could 
see dimly through the fog. From this shingle we made 
a collection of rocks, and although none of them were 
seen in situ, it has seemed best to describe them because 
they presumptively represent the material of the neigh¬ 
boring cliffs, and because information as to the geology of 
the island is meager. Dr. Dawson figures grey biotite- 
