162 F. BASCOM 
crystals are, in many instances, bordered with a narrow edge of 
radiating zeolite needles. In association with this alteration is 
an alteration to colorless, brilliantly polarizing muscovite. The 
nepheline also weathers into an irresolvable, granular, whitish, 
dimly polarizing substance which may be kaolin. Some of the 
powdered rock, from which was excluded all phenocrysts except 
nepheline, was tested for the alkalies. Three-tenths of one gram 
of this powder, ef which about one-half was nepheline, showed 
an alkali contents follows: soda, 8.32 per cent.; potash, 7.08 
per cent. A sample of the powdered nepheline, very nearly 
pure, gave soda, 7.70 per cent.; potash, 3.74 per cent. The pres- 
ence of a potash feldspar, as an orthoclase, in the groundmass 
would account for the high potash percentage in the first sample. 
Augite —Augite occurs in unmistakable, idiomorphic crystals 
of a violet color. There is a manifest pleochroism. ¢= violet. 
a=green. The crystals are frequently bounded by the prismatic 
and pinacoidal planes, giving octagonal cross-sections. Twinning 
parallel to the orthopinacoid is present, and zonal structure is 
not uncommon. Inclusions of apatite and magnetite are abund- 
ant. More rarely are found inclusions of olivine. The peripheries 
of the crystals show a narrow border of alteration to a uralitic, 
or to a reddish brown, hornblende. 
Hornblende.—This mineral occurs both as phenocrysts and as 
a constituent of the groundmass. In the former case it is a rich 
red brown, with marked pleochroism and absorption. ¢—reddish 
brown. @=vyellowish green. Cross sections show the horn- 
blende angle. The hornblende-phenocrysts are not so numerous 
nor so large as the augite-crystals. 
In the groundmass the slender lath-shaped, frayed crystals 
of a pleocroic reddish brown or a green hornblende are a con- 
spicuous feature. These, which are abundant, together with 
biotite, augite and magnetite, are distributed through a colorless 
feldspathic matrix and constitute the dark-colored constituents 
of the groundmass. An alkali feldspar, a secondary muscovite, 
and minute specks of calcite constitute the colorless portion of 
the groundmass. The presence of calcium carbonate is attested 
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