REVIEWS 787 



cussed in detail. The oil is believed to have been derived from the two 

 organic shales, and apparently each gave rise to a different type of 

 oil — the Moreno to a light paraffin oil and the Kreyenhagen to a heavy 

 asphalt oil. The diatoms are believed to have been the greatest contri- 

 butors in the formation of the oil. 



H. R. B. 



Mineral Resources of Alaska for 1914. By Alfred H. Brooks 

 and Others. U.S. Geol. Surv., Bull. No. 622, 1915. Pp. 380, 

 pis. 11, figs. 8. 



This volume is the eleventh of a series of annual bulletins summariz- 

 ing the results of the investigations of Alaskan mineral resources and 

 the status of the industry in the territory. Fourteen papers deal with 

 the mineral resources of certain districts. 



The gold and copper deposits of the Port Valdez district are descibed 

 by B. L. Johnson. The country rock includes basic lavas, slates, gray- 

 wackes, and other sediments of Mesozoic age. Gold occurs in quartz- 

 filled fissure veins formed at moderate depths; the copper chiefly as 

 sulphide impregnations and replacements of sheared zones along the 

 fractures. The mineral association in both gold and silver ores is 

 practically the same, varying only in relative proportions. The sulphide 

 minerals are pyrite, chalcopyrite, galena, sphalerite, and some pyr- 

 rhotite and arsenopyrite. There was but one period of mineralization. 

 As in the Ellamar district, both types had a common origin in solutions 

 that circulated subsequent to late Mesozoic intrusions, with which they 

 were probably genetically related. 



P. S. Smith and A. G. Maddren describe the quicksilver prospects 

 of the Kuskokwin region. The ore occurs in brecciated zones in Cre- 

 taceous sandstones and shales at the contacts of granitic and andesite 

 dikes. Cinnabar, generally with stibnite, occurs in quartz veinlets 

 and stringers. In places calcite and siderite are present. Some cinnabar 

 has also been obtained from placer gravels, and detritus in a stream near 



one of the deposits contains native mercury. 



H. R. B. 



