102 REVIEWS 



glacial streams which are independent of the present topography of the 

 valleys. 



Glaciers are now the most important erosive agents in the Sarek- 

 gebirge. Because of the altitude, frost, ice, and daily temperature range 

 have developed extensive rock-fields, or on steep slopes, large talus piles. 

 Deltas have, in a number of places, been built in the lakes by the heavily 

 mud-laden streams from the glaciers. As an indication of the immense 

 amount of post-glacial filling may be cited the extinction of one or more 

 considerable lakes by this process. 



R. C. M. 



A Geologic Reconnaissance of a Part of the Rampart Quadrangle, 

 Alaska. By Henry M. Eakin. Bull. U.S. Geol. Surv. 

 No. 535, 1913. Pp. 38. 

 This report takes into account the Rampart and Hot Springs district which 

 include most of the triangular area between the Yukon and Tanana rivers 

 west of longitude 150 , and a strip of territory on the north side of the Yukon 

 that extends nearly to longitude 154 . The base of the geologic column is 

 formed by a series of metamorphic rocks which consists of probable Silurian 

 and Devonian limestones and schists, late Paleozoic greenstones (that contain 

 some sedimentary beds), early Mesozoic slates, sandstones, and conglomerates, 

 Cretaceous and older slates, quartzites, and schists. All of these beds are 

 closely folded. The metamorphic series is overlain locally by Eocene beds 

 which represent part of the notable fluviatile deposition of Eocene time, 

 "evidence of which is widespread in Alaska." The strata are considerably 

 folded and faulted. A good part of the region is mantled by Quaternary silt, 

 sand, and gravel deposits. The silt is probably of glacial origin. The igneous 

 rocks consist of probable late Paleozoic rhyolite flows, tuffs, and flow breccias, 

 probably late Paleozoic basic flows, tuffs, diabase, glassy lavas, and tuffs, 

 late Mesozoic or early Tertiary monzonite sills and batholiths with numerous 

 dikes. Erosion occurred in post-early Mesozoic, post-Lower Cretaceous, post- 

 Upper Cretaceous, and in post-Tertiary times. Placer gold is the only mineral 

 of economic importance. The gold and silver production of the Rampart dis- 

 trict is decreasing while that of the Hot Springs district is rapidly increasing. 

 The largest output of the latter district was in 191 1. The placer gold has been 

 derived from quartz veins in the old metamorphic rocks, from carbonaceous 

 beds, and from hematite deposits in the neighborhood of monzonite. The 

 placers are of two types — those of present stream and those of terrace gravels. 

 Pebbles of cassiterite occur with the gold in the Sullivan Creek placers but 

 are not worked to any extent. 



V. O. T. 



