46o REVIEWS AND BOOK NOTICES 



Geology of the Central Copper River Region, Alaska. By Walter 

 C. Mendenhall. (U. S. Geological Survey, Professional 

 Paper No. 41, 1905.) Pp. 133, 20 plates and maps, 11 figures. 



The area described lies in the central and northern parts of the copper 

 River Ba->in — one of the most interesting regions in southern Alaska. It 

 came iito prominence in 1898, at the time of the great stampede to the 

 Eldorado of the north. Some of those who overcame the difficulties of 

 getting into the Copper River country were rewarded by finds of consider- 

 able copper and gold deposits. 



Three great mountain ranges cross the area — the Chugatch, the Wran- 

 gell, and the Alaskan. Mount Wrangell itself is an active volcano which 

 constantly gives forth great volumes of smoke and vapors. Mount San- 

 ford, one of a number of extinct volcanoes, is 16,200 feet high — the highest 

 peak in the region. The southern side of the Alaskan range is a great 

 fault scarp, and Mr. Mendenhall beheves the whole Copper River valley 

 to be due to a sunken fault block. He also thinks it probable that this 

 sinking was the result of the outpouring of the Wrangell lavas. 



Another interesting scientific contribution is the description of 6,000- 

 7,000 feet of Permian strata in the upper Copper River valley. The fauna 

 is much more closely related to that of the great hmestones of India than 

 to the fauna of the Mississippi valley Permian. This is probably one of 

 the best developments of marine Permian in the world. E. W. S. 



Geology of the Boulder District, Colorado. By N. M. Fenneman. 



(U. S. Geological Survey, Bulletin No. 265, 1905.) Pp. loi, 



5 plates, II figures. 

 The principal topic of this report is the gas and oil of the district, but 

 it treats also of the physiography, stratigraphy, structure, geologic history, 

 and its other economic resources. These are: water, building-stone, 

 grindstone, hme, clays, and coal. The area lies at the foot of the Front 

 Range, and has its appropriate topography of plains on the east, and 

 mesas and foothills on the west. The rocks are nearly horizontal sedi- 

 mentaries on the east, and the upturned edges of the same against the 

 Archean mass on the west. The oil-producing formation is the Pierre. 

 The producing wells are in a narrow north-south belt, which was found 

 to be the area of a monoclinal fold. Shooting of wells was found to have 

 an injurious effect in many cases, the flow of such wells decreasing after 

 the shooting. Thirty-nine thousand barrels of oil were produced in 1903. 

 One gas well furnishes 3,000,000 feet per month. E. W. S. 



