22 GENERAL GEOLOGY 



glacier of that name. It consists of sharply idiomorphic 

 crystals of brownish-green hornblende up to an inch and 

 a half in length, embedded in grayish-white granular feld- 

 spar having the composition of an acid labradorite, all per- 

 fectly fresh. In the same specimen is seen granular dio- 

 rite of the normal type, so that its porphyritic form is 

 probably only a local phase of the tonalite. At the same 

 spot was found an abundance of boulders of hornblende- 

 schist, mica-schist and staurolite-schist similar to the 

 specimens from the same vicinity described in Reid's 

 report. 



SKAGWAY AND WHITE PASS 



Around Skagway and along the White Pass railroad to 

 the summit are granitoid rocks, with basic segregations 

 and later diabase dikes. The rock forming the bluffs east 

 of the railroad station and pier is a coarse white granitoid 

 tonalite (35) made porphyritic in aspect by the black 

 biotite crystals. The feldspar is almost wholly a coarse 

 plagioclase, twinned on two laws. It is an oligoclase al- 

 bite with zonal extinction from 3 to + 16 on M(oio). 

 The biotites are full of beautiful zircons. There is a 

 small amount of green hornblende. The rock is cut here 

 by a dike of aplite (34) a foot wide. Quartz phenocrysts, 

 with biotite and muscovite, are visible in this aplite, and 

 the whole ground has an exquisite minute granophyric 

 structure in radiating feathers. 



At Glacier Station and at White Pass summit is a 

 coarse subporphyritic biotite-granite (42). The flesh- 

 colored feldspar is an exceedingly fine-grained microcline 

 microperthite ; the white is a coarsely twinned plagio- 

 clase. At Glacier Station segregations of diorite in the 

 granite are abundant from 4 inches to 2 feet in width, as 

 well as white aplitic segregations. The diorite (40) is a 

 fresh, black, hornblende-biotite rock, containing titanite 

 visible with the lens. The hornblende has the strongest 



