CHICHAGOF COVE 
83 
crysts are chiefly hornblende, strongly pleochroic, light brown to pale 
yellow, frequently twinned. In several cases cores of colorless diop- 
side are enclosed by the hornblende in parallel position, the boundaries 
between them irregular but sharply marked. The hornblende is clearly 
original. Epidote in grains and short prisms filling cavities of irregu¬ 
lar shape is present in all the slides. 
The rock is a hornblende-alkali-syenite-porphyry . 
In no. 98 the groundmass is somewhat coarser, and in addition to 
the hornblende phenocrysts are a few ill-defined feldspars which 
appear to have the composition of oligoclase. Careful search of the 
slides for nepheline failed to reveal its presence. 
Nos. 95, 96, 97, 100, 101 and 102 are specimens from different 
parts of the same dike, which outcrops on the shore of Stepovak Bay 
at East Point with a width of ten feet, and again a half mile to the 
north in a gulch near the camp, where it is six feet wide. The dike 
is nearly vertical, and its general course is about at right angles to the 
sedimentary rocks which it cuts, but in the gulch it turns abruptly into 
the strike of the beds, and was followed some distance as a sill. The 
rock is dull grey in color, fine-grained and compact near the walls of 
the dike, but coarser at the centre and slightly amygdaloidal, the cavi¬ 
ties filled with fibrous laumontite and calcite. Prisms of black horn¬ 
blende are sparingly present through its whole mass, here and there 
aggregated to radial groups. Isolated glassy feldspars are also visible. 
In thin section the groundmass is seen to be entirely similar to that 
of the last rock, consisting of laths of albite and grains of augite and 
magnetite. The phenocrysts are very slender prisms of hornblende, 
anhedra of diopside and occasional anhedra of albite. They are few 
in number, however, compared with the phenocrysts of hornblende of 
the first rock described, and herein consists the principal difference 
between the two rocks. 
No. 81. This rock is from a dike cutting the shales on the lower 
slopes of Chichagof Peak. It is rather coarsely granular, of a green¬ 
ish-grey color, and appears to the eye to be in an advanced stage of 
alteration. In thin section it appears quite fresh, however, and is 
found to be holocrystalline and almost ophitic in structure. It is com¬ 
posed of a network of laths of plagioclase feldspar, varying in com¬ 
position from albite to acid oligoclase, with which are numerous 
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, 
