Reviews 



Geology and Mineral Resources of Kenai Peninsula, Alaska. By 

 G. C. MARtiN, B. L. Johnson, and U. S. Grant. U.S. Geol. 

 Surv., Bull. 587, 1915. Pp. 243, pis. 2>^, figs. 43. 



This volume is a summary of what is known of the geology and 

 mineral resources of the Kenai Peninsula, including both the results of 

 the early investigations and the hitherto unpublished work of the 

 present writers. In an introductory chapter Martin summarizes the 

 geology of the general region; the succeeding chapters are devoted to 

 a more detailed discussion of its several parts. The relations of highly 

 folded pre-Tertiary sediments and associated lavas and intrusives of 

 the Kenai Mountains are as yet imperfectly known. Rocks definitely 

 assignable to the Triassic and to the Jurassic are known over hmited 

 areas, but the great bulk of the slate and graywacke series has not been 

 differentiated. It may include upper Paleozoics and possibly some 

 Mesozoics younger than the Jurassic. The Sunrise group of earlier 

 writers probably represents the upper part of this series and seems to 

 be more nearly equivalent to the Orca group than to the Valdez group 

 in the Prince Wilham Sound region. The only Tertiary beds of the 

 Kenai Peninsula are those of the non-marine Kenai formation. 



The gold lodes of the northern Kenai Peninsula are described by 

 B. L. Johnson. The deposits are of three general types — fissure veins, 

 stringer lodes, and mineralized silicic dikes. The veins occur in two 

 distinct sets, standing approximately at right angles to each other and 

 dipping at high angles. Both sets of fractures are ore-bearing and of 

 about the same age. Their average thickness is between 2 and 2^ 

 feet. The present known vertical range of these veins is about 5,000 feet. 

 Of minor importance are the stringer lodes, characteristically developed 

 in the slates and graywackes parallel to the cleavage and bedding planes. 

 Only slightly mineralized dikes have been discovered thus far. The 

 mineralogical composition of the veins is simple and indicates deep- 

 seated conditions of origin. Quartz is the predominant gangue mineral, 

 Calcite is generally present and albite locally. Arsenopyrite, galena, 

 sphalerite, and pyrite are the characteristic sulphides, arsenopyrite 

 being most abundant. Chalcopyrite and pyrrhotite are less common. 



61 



