44 ALASKA GEOLOGY 



The stream tributaries could be seen to come down from 

 the hills in the background, which seemed from the ship 

 to be quite modern volcanoes and to retain the crater 

 form. We had not time to reach these hills over the 

 tundra, but the large and half-worn fragments of an erup- 

 tive rock which we found in the bed of the stream seemed 

 certainly to come from them. 



The rock is an amphibolite derived from an eruptive 



pyroxenite(i77). 

 It is of a dull pale 

 greenish color, is 

 full of rust- 

 stained fissures, 

 and though evi- 

 dently altered 



FIG. II. COAST OF PORT CLARENCE, ALASKA. SnO WS TCmainS 



of broad augite cleavage surfaces. Under the micros- 

 cope appear cores of pale amber augite mostly changed 

 to a fine felted mass of actinolite needles. There are 

 many grains of titaniferous magnetite bordered by broad 

 bands of fine opaque white leucoxene. The broad patches 

 of augite show no trace of intervening feldspar. 



Another slide shows that some of the same material 

 has been further changed into isotropic serpentinous matter 

 full of rhombs of dolomite. 



The rocks exposed in the cliff along the shore are slates 

 of the Vancouver Series, to be described below. 



THE VANCOUVER SERIES 



A series of dark slates, sandstones, greywackes, tuffs, 

 and subordinate calcareous beds, often strongly cleaved, or 

 jointed all to pieces, and filled with quartz veins, but 

 otherwise not greatly advanced in metamorphism, is 

 widely distributed in Alaska. It extends from Vancouver 

 Island on the south, past Sitka and Glacier Bay to 



