7° 
ALASKA GEOLOGY 
without any pretense to accuracy, intended only to show 
the general relative distribution of the various formations 
discovered. 
VICINITY OF SAND POINT, POPOF ISLAND 
Dali in his report on Coal and Lignite of Alaska* states 
that the northwestern part of Popof Island, near Sand 
Point, is composed of sandstones and conglomerates sim¬ 
ilar to those of the Kenai Formation in Coal Bay on the 
neighboring Unga Island. u They are broken and cut by 
dikes and larger intrusions of basaltic lava and diorite and 
near the contacts are much altered and intersected by 
veins of chalcedonic quartz.” 
I did not see this sedimentary formation. The point 
south of the harbor at Sand Point was visited, and seemed 
to be made up wholly of lavas and volcanic tuff; and 
similar rocks were found on the northern shore of the 
island at a bluff about three miles from Sand Point. 
The lavas at Sand Point were found to be augit e-an¬ 
desite and augite-hyftersthene-andesite . They are dark 
grey compact rocks showing glassy feldspar crystals in 
a dull groundmass. Under the microscope the struc¬ 
ture is strongly porphyritic (slides 125, 126), the most 
abundant crystals being large fresh plagioclase feldspars 
with extinction angles of labradorite, abundantly twinned 
but very slightly zoned, and full of inclusions of glass. 
Augite, colorless or pinkish, is also present, but is largely 
altered to green serpentine. One slide (127) shows abun¬ 
dant hypersthene, sharply idiomorphic, with characteristic 
double refraction and faint pleochroism; some hypersthene 
crystals are enclosed in augite crystals in parallel position. 
The groundmass contains microlites of feldspar and augite 
in a glassy base. 
Beneath the heavy masses of these very fresh lavas, 
1 17th Ann. Rep. U. S. Geol. Survey, Pt. 1, p. 808. 1896. 
