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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 Excerpt:...larger anhedra of orthoclase, determined by their lower refractive index and lack of twinning. The interspaces of the feldspars are occupied by grains of colorless pyroxene (diopside) partly altered to serpentine, together with fairly abundant magnetite. The rock differs materially from the preceding alkali-syenite-porphyries, both in structure and in the absence of hornblende, but it is nevertheless, though with some doubt, classed with them. Many other dikes, from which specimens were not collected, appeared to consist of rocks similar to those just described, so that the characteristic dike rock of the region may be considered an alkali-syenite-porphyry. LATITE No. 94. On the lower slope of Chichagof Peak, just above the little lake, and cutting the lower Stepovak beds (breccias), is a narrow dike of a black glassy-looking rock, weathering into spheroidal forms. Glassy feldspar phenocrysts are abundant in the aphanitic groundmass. Studied in thin section, this rock proved to be wonderfully fresh and lava-like in appearance. In a groundmass of brown glass crowded with microlites of plagioclase feldspar and augite, are numerous phenocrysts of labradorite, orthoclase and augite. The smallest feldspar microlites seemed to have the same character as the most abundant phenocrysts, which were determined as basic labradorite by extinctions of complex albite-Carlsbad twins. The phenocrysts contain numerous inclusions of glass, which are grouped parallel to the outlines of the crystal and are in part altered to chlorite. But the feldspar itself appears perfectly fresh and unaltered. The orthoclase, which is less abundant than the labradorite, offers many points of interest. It is in anhcdra with subangular and often rounded and deeply embayed outlines. Some are qu...