24 ALASKA GEOLOGY 



magnetite grains, crystals of green mica, and abundant grains and 

 prisms of epidote. A rock of uncertain origin. 



Quartz-biotite-diorite (189). Snow-white feldspars with large 

 sharp crystals of biotite. 



Gneiss oid biotite-granite (193). A fine-grained greyish granite 

 with distinct banding brought about by parallelism of biotite plates. 



Black micaceous quartzite (277). 



With these crystalline rocks are probably to be grouped other boul- 

 ders found on the shores of Yakutat Bay coarse crystalline marble 

 with black veins (292), coarse pegmatite with felted actinolite needles 

 (291), poikilitic mica-diorite (279), and fine-grained epidote-chlorite- 

 schist (278). 



PRINCE WILLIAM SOUND 



As in Yakutat Bay so also in Prince William Sound we 

 found the rocks to consist mainly of the sandstones and 

 shales of the Vancouver Series or of the closely similar 

 Valdes Series of Schrader. Reference will be made to 

 these later, in the section devoted to these rocks. At 

 Landlocked Bay and at Virgin Bay the rocks seemed to 

 have a different character. We went ashore at Land- 

 locked Bay, the vertical walls of which shut us in 

 like a well, and climbed several hundred feet over a 

 wall of serpentine to the adit of a copper mine. The de- 

 posit of copper ore is a mass of quartz, with chalcopyrite, 

 pyrrhotite, and small amounts of galena and sphalerite, oc- 

 cupying a shear zone in a rock of serpentinous charac- 

 ter. Thin sections of this rock (186) showed a mass of 

 fibrous serpentine in which are embedded shattered crys- 

 tals of perfectly fresh labradorite and abundant augite, 

 raveled out on the edges to colorless hornblende and 

 serpentine. There are still traces of ophitic structure, and 

 the rock is evidently a sheared and partly serpentinized 

 diabase. 



At Virgin Bay we found the rocks at the shore for 

 a great thickness impregnated with pyrite and chalcopy- 



