164 abstracts: geology 



(4) Gold-bearing veins and sheeted zones in quartzite. B. Replace- 

 ment deposits related to fissures or to bedding planes. (1) Silver- 

 bearing replacement veins in sedimentary rocks, (2) Silver deposits in 

 bedding-planes of calcareous rocks, (3) Gold-bearing replacements veins 

 in sedimentary rocks. C. Replacement deposits of contact meta- 

 morphic origin. (1) Gold-copper deposits, (2) Magnetite deposits. 

 D. Gold placers. 



All the important deposits in place are in or near the intrusive bodies. 

 They were deposited by ascending solutions, and it is regarded as prob- 

 able that these solutions were given off from the intrusives now exposed 

 or from deeper ones that are still concealed. F. C. C. 



GEOLOGY. — Geology of the Nome and Grand Central quadrangles, 

 Alaska. Fred H. Moffit. U. S. Geological Survey Bulletin 533. 

 Pp. 140, with maps and views. 1913. 



The Nome and Grand Central quadrangles are situated in the south- 

 central part of Seward Peninsula, Alaska. 



Along the southern border of the area is a narrow coastal plain, 

 sloping gently upward from Bering Sea to the foot of the hills a tew 

 miles inland while on the north side are the Kigluaik Mountains, whose 

 highest peaks within the quadrangle are about 3,000 feet. The rest of 

 the area is a dissected upland with hills reaching a maximum elevation 

 of about 2600 feet and shoA\ing smooth rounded contours. 



The oldest rock formation is the Tigaraha schist, the topmost mem- 

 ber of the Kigluaik group, which consists of l)iotite gneisses, coarsely 

 crystalline limestone, biotite schist, and siliceous graphitic schist. 

 The Tigaraha schist is exposed in the most northern part of the area 

 and has a general southerly dip. It is intruded by dikes and sills of 

 granite, diorite and diabase. Overlying the Kigluaik group and occu- 

 pying nearly aU the remainder of the mapped area is the Nome group 

 of formations, made up chiefly of chloritic and feldspathic schists and 

 altered limestones Avith many greenstone and a few granite intrusives. 

 The a^e of the Kigluaik and the Nome groups is unknown. They 

 probably range from Paleozoic or pre-Paleozoic to middle Paleozoic. 

 The Quaternary unconsolidated deposits of the area include sands and 

 gravels of marine and of fluvial origin, glacial deposits, and the mantle of 

 unassorted debris due to weathering. 



Within the coastal plain five or six of the old beaches have been dis- 

 covered and these give direct evidence of changes in the relative heights 

 of land and sea. They range in elevation from 34 feet below sea level 



