320 abstracts: geology 



GEOLOGY. — The Upper Chitina Valley, Alaska. Fred H. MoFFiT. 

 U. S. Geol. Survey Bull. 675. Pp. 80, 13 plates, 2 figs. 191 8. 

 This report deals largely with the more purely scientific aspects of 

 the geologic problems, discussing at considerable length the stratig- 

 raphy and the igneous rocks. It has been proved that the copper- 

 bearing rocks, which have yielded valuable deposits in the lower Chitina 

 Valley, occur also in the upper valley. It is also shown that the forma- 

 tions from which the Nizina placers have derived their gold occur in this 

 region. On the other hand, no mineral deposits of proved value have 

 yet been exploited in the upper Chitina basin. It must be said, however, 

 that comparatively little prospecting has been done in this field. 



R. W. Stone. 



GEOLOGY. — The Nelchina-Susitna Region, Alaska. Theodore 

 Chapin. U. S. Geol. Survey Bull. 668. Pp. 64, 10 plates, 4 figs. 

 1918. 

 Discusses the distribution, age, and correlation of the various geologic 

 formations in a little-known region, and the development of its land 

 forms. There has been but little productive mining in the region, and 

 its geology does not encourage the hope of finding extensive placers, 

 yet the wide distribution of alluvial gold indicates considerable mineral- 

 ization. Moreover, the presence of a large number of intrusive igneous 

 rocks also encourages the hope of finding local mineralization of the 

 bedrocks. R. W. Stone. 



GEOLOGY.— r/te Nenana coal field, Alaska. G. C. Martin. U. S. 

 Survey Bull. 664. Pp. 54, 12 plates. 1919- 



The Nenana coal field lies southwest of Fairbanks in the northern 

 foothills of the Alaska Range. The rocks of the Nenana coal field con- 

 sist of the coal-bearing beds, metamorphic and igneous rocks beneath 

 the coal -bearing beds, and gravel, sands, and silts above them. 



The coal-bearing strata consist of slightly consolidated sands, clays, 

 and gravels with numerous beds of lignite. These beds are of Tertiary 

 age. The coal -bearing beds rest unconformably upon Paleozoic (?) 

 schist and igneous rocks and are overlain unconformably by Quarternary 

 gravels, 1,500 or 2,000 feet thick. 



The structure of the coal areas is fairly simple. The individual coal 

 areas consist of shallow and gently warped basins in which the beds are 

 at some places steeply folded or faulted against masses of crystalline 



