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, 



