abstracts: geology . 603 



The upper part of the Fort Union formation occupies all of the center 

 of the Bull Mountain region and contains the principal coal beds. It 

 is composed of sandstone in beds ranging from a fraction of a foot to 

 50 feet or more in thickness, interbedded with a somewhat larger pro- 

 portion of clay shale, shale, and numerous beds of coal. 



Within the upper part of the formation there are 26 coal beds, ranging 

 in thickness from 1 foot 2 inches to 15 feet. From the abundance of 

 fossil leaves and fresh-water shells and the numerous beds of coal it is 

 evident that the formation was deposited in fresh or nearly fresh waters, 

 probably inland lakes or ancient estuaries on whose shores grew luxuri- 

 ant vegetation. 



All coal in this field may be classed as high-grade black lignite or 

 subbituminous. Most of the coal beds are lenticular, showing a wide 

 variation in thickness at different points on the outcrop. The coal 

 beds are described and analyses given. The greater part of the volume 

 is detailed description of the geology by townships. R. W. Stone. 



GEOLOGY. — Mineral resources of the Kantishna region, Alaska. 

 S. R. Capps. U. S. Geological Survey Bulletin 662-E. Pp. 

 53, with maps, sections, and illustrations. 1917. 



The region discussed lies on the north side of the Alaska Range and 

 includes portions of the basins of Nenana and Kantishna rivers. 



The rocks of the Kantishna region range from highly metamorphic 

 mica schists and gneisses, through less altered but deformed sediments 

 of Paleozoic age, to the slightly indurated Tertiary coal-bearing beds 

 and to the unconsolidated terrace gravels and the deposits of present 

 streams. 



The prevailing structural trend of the region is east-northeast, 

 parallel to the axis of the Alaska Range, and has been determined by 

 movements similar to those which brought the present range into 

 existence. 



The productive gold placer deposits of the Kantishna district all 

 occur in the basins of the streams that head in the Kantishna Hills 

 and radiate in all directions from the higher peaks. Paying deposits of 

 gold placer gravel were found in 1905 and 1906 on all the streams that 

 are now productive except Little Moose Creek. 



The entire Kantishna mining district lies in an area in which the 

 underlying rock is the Birch Creek schist, cut by relatively small 

 bodies of intrusive rocks. Among these intrusives are some dikes and 



