abstracts: geology 161 



deeper " hard" ore, 37 per cent metallic iron and 20 per cent lime. This 

 composition of the "hard" ore holds from about 400 feet to the greatest 

 depths reached, even to 2000 feet in bore holes over a mile from the out- 

 crop. C. B. 



GEOLOGY.— The Sitka mining district, Alaska. Adolph Knopf. 

 Bulletin U. S. Geological Survey, No. 504. Pp. 32, with maps and 

 sections. 1912. 



The Sitka mining district comprises Chichagof, Baranof, and Kruzof 

 islands, together with a few smaller islands. The total land area roughly 

 approximates 4500 square miles, the greater portion of which is included 

 in Chichagof and Baranof islands. 



The rocks lie in broad belts, which strike northwest and southeast, con- 

 forming thus with the prevailing structural trend of southeastern Alaska. 

 The cores of the islands are made up largely of granitoid rocks, mainly 

 quartz diorites, which, as a rule, have been intruded parallel to the strati- 

 fied rocks. 



The ore deposits are auriferous lodes, commonly occupying shear 

 zones in graywacke. Two mines, both of which are situated at Klag 

 Bay on the west coast of Chichagof Island, have so far been productive. 

 The ores, which range in value from $15 to $90 a ton are of higher grade 

 than the general gold ore of southeastern Alaska, which in 1910 averaged 

 $2.78 a ton. A large number of ore bodies of the same general character 

 have long been known to occur near Sitka, but owing to their low grade 

 none has yet been brought to a producing stage. A. K. 



ECONOMIC GEOLOGY.— Coals of the State of Washington. E. Eggle- 

 ston Smith. Bulletin U. S. Geological Survey, No. 474. Pp. 

 206, with maps and views. 1911. 



Washington coals range from low-grade subbituminous to anthracite; 

 but as the anthracite owes its character to metamorphism by igneous 

 intrusions, it is of slight extent and limited range. In general, the highest 

 grade of coal is found near the Cascade Range and the quality decreases 

 westward from the mountains. 



This is the first thoro systematic attempt to study the quality and 

 character of the Washington coals. Every mine in the State was visited 

 and from one to eight samples were obtained from each bed of coal mined, 

 the samples being analyzed at the Pittsburgh Laboratory of the Bureau 

 of Alines. Each mine is briefly described, and the location of each sample 

 is recorded, with a section of the coal bed at that point. The physical 

 characteristics of the coals and the effects of various impurities are fully 

 treated. 



