REVIEWS 479 



tudc, the Arctic Circle and 68° north latitude. The sedimentary rocks are 

 divided into undifferentiated Paleozoic metamorphic schists, undifferentiated 

 Paleozoic limestones, Silurian limestone, Upper Devonian limestone, Mississip- 

 pian beds (Noatak sandstone, Lisburne limestone), a probable Jurassic 

 Anaktuvuk group, a Lower Cretaceous or Upper Jurassic Koyukuk group, 

 an Upper Cretaceous Bergman group. Eocene conglomerate, Pleistocene, and 

 Recent. The igneous rocks consist of greenstones (pre-Carboniferous), prob- 

 able Jurassic basic intrusives, flows, and tuffs, granitic intrusives (pre-Upper 

 Cretaceous), and late Tertiary to Recent basaltic flows and volcanic ash. 

 Deformation followed by erosion occurred previous to the deposition of the 

 undifferentiated Paleozoic limestones. A period of deformation closed the Mis- 

 sissippian. The present topographic features were produced after the depo- 

 sition of part of the Eocene. A series of east-west folds, broken by faults, 

 affect the eastern part of the area, while north-south folds and faults are present 

 in the western part. Auriferous gravels of notable production occur in the 

 Shungnak and Squirrel River regions. There are gold and copper sulphide 

 lodes, which have not as yet been developed to the producing stage. 



V. O. T. 



A Geological Reconnaissance of the Fairbanks Quadrangle, Alaska. 



By L. M. Prindle. With a Detailed Description of the 



Fairbanks District, by L. M. Prindle and F. J. Katz. And 



an Account of Lode Mining near Fairbanks, by Philip S. 



Smith. Bull. U.S. Geol. Surv. No. 525, 1913. Pp. 216. 



The Fairbanks quadrangle, which forms a portion of the central plateau 



province of Alaska, lies between 64° and 66° north latitude and 146° and 150° 



west longitude. The most prominent structures are northeast-southwest 



trending close folds. The oldest rocks belong to the pre-Ordovician ( ?) 



Birch Creek schist; separated by an unconformity, a series of Paleozoic rocks 



(Ordovician to Carboniferous) follow. Unconformities also exist between the 



Silurian and early Devonian, between later Devonian and probable Pennsyl- 



vanian rocks, between the Upper Cretaceous and older rocks, and between the 



Upper Cretaceous and probable Eocene lignite-bearing beds. The occurrence 



of greenstones (basic volcanic lavas and tuffs), which are probably in the main 



of Devonian age, is interesting inasmuch as similar rocks appear in many 



parts of Alaska which are apparently of about the same age. The intrusion 



of granites and diorites succeeded the deposition of the Pennsylvanian strata. 



In one locality a basalt flow of probable Tertiary age was noted. 



In the detailed description of the Fairbanks district are brought out the 

 facts that this district lies wholly within the area of the Birch Creek schist, that 

 great intrusions of diorite, granite, porphyries, and dikes occurred probably 

 at the close of the Mesozoic, and that the auriferous and other deposits are 

 genetically related to the intrusions. Gold placers have been developed on a 



