1 6 GENERAL GEOLOGY 



On the beach were boulders of granite, vein-quartz, amphibolite, 

 hornblende-gabbro, diabase, etc. 



Under the microscope the rocks of this section were found to be as 

 follows : 



1. Schists. Quartz-zoisite-schist (47). An extremely fine quartz 

 mosaic, with parallel structure produced by sericite and biotite plates. 

 Very abundant grains and laths of zoisite, some epidote, and titanite 

 surrounding ilmenite. Quartz-epidote-schist (41). Much the same 

 as the last, but with more epidote than zoisite, and chlorite as well as 

 sericite. 



These rocks may well be altered sediments, but the recrystallization 

 is complete and their original character not certain. 



2. Greenstone (45 and 46). Amphibolite. A fine-grained aggre- 

 gate of hornblende needles, plates of chlorite and sericite, and grains 

 of quartz and epidote, with some zoisite. A slight appearance of 

 coarse porphyritic structure, as though feldspar phenocrysts had been 

 present in the original rock. Probably derived from a diorite-por- 

 phyry, or similar igneous rock. 



3. Arkose (44). An aggregate of angular fragments of quartz, 

 orthoclase, and plagioclase, cemented with granular quartz, limonite 

 and pyrite. All the larger fragments show pronounced cataclastic 

 structure and wavy extinctions. 



WRANGELL AND NORTHWARD 



At Wrangell the hill north of the town presents the 

 following section (fig. 3) : 



s. 



FIG. 3. SECTION NORTH OF WRANGELL, ALASKA. 



1. Soft blue slate. 



2. Hard blue slate, with sandy and micaceous layers. 



3. Coarse granitoid metamorphic sandstone (arkose). 



4. Very siliceous biotitic sandstone. 



These rocks, which in the field present the appearance 

 of but slightly metamorphosed sedimentaries, give sur- 

 prising results when studied under the microscope. They 

 prove to be highly feldspathic and almost entirely recrys- 



