1 8 GENERAL GEOLOGY 



ments of colorless augite crystals which in places are 

 bordered by colorless secondary hornblende needles. No 

 trace of feldspar could be found. The rock seems to have 

 been derived from a pyroxenite consisting chiefly of diop- 

 side. The schistose character is produced by shearing 

 along the most serpentinized bands, and the shattered con- 

 dition of the remaining augite crystals is good evidence 

 that such shearing has taken place. 



A great variety of rocks were seen in the boulders on 

 the shore, tonalites like those farther south, diorite, gar- 

 netiferous gneisses, etc. 



At Juneau Mr. Palache remained for several days and 

 made a special study of the Treadwell mine, upon which 

 he makes a special report in this volume. 



We saw at Sitka the first certain outcrops of the Van- 

 couver Series, which we traced northward to Port Clar- 

 ence by a small group of peculiar fossils, and which is 

 made the subject of a separate chapter, page 42. 



At various places in the vicinity of Sitka these sedi- 

 mentary rocks are traversed by granitic dikes. The 

 granite (58) is coarse granular to fine porphyritic in text- 

 ure, and consists chiefly of quartz and orthoclase, with con- 

 siderable acid oligoclase and sparing biotite, largely altered 

 to chlorite. Both orthoclase and oligoclase are occasion- 

 ally developed in porphyritic crystals with sharp boun- 

 daries. 



Cutting the granite, near the Hot Springs, are several 

 narrow dikes of a dark rock looking like diabase, but 

 which, on examination with the microscope, proved to be 

 a lamprophyre of the uncommon species spessartite, ac- 

 cording to the definition of that rock by Rosenbusch. It 

 is a compact, fine-grained rock (62) with panidiomorphic 

 granular structure, consisting of minute interlaced prisms 

 of brown hornblende and about equal amounts of twinned 

 and untwinned feldspar with subordinate amounts of diop- 



