130 abstracts: geology 



GEOLOGY. — The geology and mineral resources of the Nizina District, 

 Alaska. F. H. Moffit and S. R. Capps. Bulletin U. S. Geological 

 Survey, No. 448. Pp. 108, with maps, sections, and views. 1911. 



The Nizina district embraces an area of about 300 square miles in the 

 Chitina River valley, on the southeast side of the Wrangell Mountains. 

 The geologic section, from the base up, comprises (1) the Nikolai green- 

 stone, not less than 4000 feet thick, made up of lava flows, (2) the Chiti- 

 stone limestone, 3000 feet thick, (3) the McCarthy shale, at least 2500 

 feet thick, and (4) the Kennicott formation, consisting of over 7500 

 feet of conglomerate, shale, and thin limestone. The Chitistone lime- 

 stone and the conformably overlying McCarthy shale are Upper Triassic. 

 They rest conformably on the Nikolai greenstone, whose age is not 

 definitely known. The Kennicott formation is Upper Jurassic or 

 possibly Cretaceous and rests on the eroded edges of the three older 

 formations. It is intruded by numerous quartz porphyry dikes, which 

 are rare in the older rocks. These four formations are closely folded, 

 but are not greatly metamorphosed. A large part of the shales, hereto- 

 fore regarded as Upper Triassic, are shown to be Upper Jurassic. 



The Nikolai greenstone is of economic importance as a source of 

 copper. Small bodies of copper ore are widely distributed through it 

 and several large bodies, notably that of the Kennicott-Bonanza mine, 

 are situated in the limestone near its contact with the greenstone. The 

 copper, dissolved by water circulating through the greenstone, was pre- 

 cipitated in shear zones and fracture planes. Chalcopyrite, bornite, 

 and chalcocite are the most important copper minerals. The Bonanza 

 ore body, a large mass of chalcocite, is beiieved to be a primary deposit. 



The placer gold of Dan and Chititu creeks is derived from small 

 quartz veins in the Jurassic shales. These veins are probably related 

 in origin to the numerous porphyry intrusions. Reconcentration of 

 the high bench gravels has produced important stream placers. 



Certain trains of rock waste that resemble glaciers in form and in 

 other respects are believed to owe their movement to interstitial ice. 



F. H. M. 



GEOLOGY. — Geology and oil resources of the Coalinga district, California. 

 Ralph Arnold and Robert Anderson. With a report on the 

 Chemical and physical -properties of the oils. Irving C. Allen. 

 Bulletin of the U.S. Geological Survey No. 398. Pp. 354, with 

 maps, sections and views. 1910. Reprinted 1911. 



The Coalinga district is a region of arid hills and mountain ridges bor- 

 dering the west side of the great interior valley of California. The his- 



