Specimen P49Se16 is from the next to the lowest flow exposed on Tuman Head, (104,475' E., 3,450' N.). According to Powers, who collected this specimen, the section here, is largely pyroclastic and rich in bombs and scoria. The flow from which the specimen was collected ranges in thickness from 10 to 20 feet. The rock is dense medium-gray (N 5) olivine-hypersthene basalt, with seriate texture. The plagioclase, in crystals as much as 3 mm in size, averages An77, judging from the average refractive index. The olivine (Fa20) is in grains as much as one-half mm in diameter, and is pale yellowish green in hand specimen. The augite grains, which are as much as 1 mm in diameter, are yellowish green in thin section. Hypersthene prisms are much smaller, on the average. Magnetite and apatite are recognizable accessories.
Geologic reconnaissance of Semisopochnoi Island, western Aleutian Islands, Alaska