400 REVIEWS 



It is to be hoped that the demand for these guidebooks will be suffi- 

 cient to warrant their revision and republication from time to time, so 

 that they may be kept thoroughly up to date. It is suggested that in 

 future editions a set of small maps of the individual states be added, to 

 give the reader a more complete geographic background for the detailed 

 route maps than is afforded by the single physical map of the United 

 States which is included in each volume. 



Bulletin 613 covers the route of the Atchison, Topeka & Santa Fe 

 Railway from Kansas City, Missouri, to Los Angeles, California, with 

 a side trip to the Grand Canyon of the Colorado. It is obtainable from 

 the Superintendent of Documents, Washington, D.C., for fifty cents, 

 postage free. 



C. W. T. 



"Diamond Fields of German South-West Africa." By C. W. 

 Boise. The Mining Magazine (London), June, 191 5, pp. 

 1-14, figs. 8. 

 These fields, which produced nearly $15,000,000 worth of diamonds 

 in the year 19 13, constitute a narrow strip along the coast in the south- 

 western part of the colony. The productive area is about 75 miles 

 long, nowhere extending more than 12 miles inland. It is a barren 

 desert, swept by the south trade winds, and has an annual rainfall not 

 exceeding 2 inches. The coastal tract is characterized by low north- 

 south ridges separated by stretches of sand and fine gravel, in which the 

 diamonds are found. The productive stratum is at the surface, and 

 averages not more than six inches in depth. The deposits are in effect 

 eolian placers, in which the diamonds have been concentrated by the 

 sifting action of the wind, which winnows out the finer and lighter mate- 

 rial. The richest concentrations are often found in streaks parallel to 

 the direction of the prevailing wind. The average size of the diamonds 

 found increases toward the southern part of the field, but their original 

 source is unknown. 



C. W. T. 



Coal Fields of Pierce County. By Joseph Daniels. Washington 



Geol. Survey, Bull. 10, 1914. Pp. 146, pis. 30, figs. 23. 



The coals of this county are all in the Puget formation of Eocene age. 



This formation consists of sandstones, shales, and coals and attains a 



remarkable thickness, estimated at 15,000 feet. The beds have been 



