V 

 58 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 3 



and chalcocite increases, the process of enrichment becomes slower in action, 

 and erosion may, in some circumstances, overtake it. With the removal of 

 some of the protecting zone of chalcocite the protore, or original pyritic 

 material, is again exposed to oxidation and a second cycle of enrichment 

 begins. F. L. R. 



GEOLOGY. — Bibliography and index of the publications of the U. S. Geological 



Survey relating to ground water. Oscar E. Meinzer. U. S. Geol. 



Survey Water-Supply Paper 427. Pp. 169, map 1. 1918. 



Gives a brief historical statement of the work done by the Survey on the 



subject of ground water and lists 609 papers (in 454 volumes) which contain 



information on ground water, of which 307 papers (in 171 volumes) relate 



primarily to this subject. It includes brief abstracts of these papers and a 



detailed index with respect to ground water topics, and contains a map of 



the United States showing areas covered by the papers listed. O. E. M. 



GEOLOGY. — The Sunset-Midway Oil Field, California. Part I. Geology 

 and Oil Resources. R. W. Pack. U. S. Geol. Survev Prof. Paper 116. 

 Pp. 179, pis. 45, figs. 15. 1920. 



The Sunset-Midway oil field lies at the south end of San Joaquin Valley, 

 in Kern County, California. Deposits of asphalt and seeps of oil in this 

 region were known to the earliest settlers, but real development did not 

 begin until 1900. Up to the end of June, 1917, more than 2200 wells had 

 been drilled in the field, and on that date 1840 were producing. Up to 

 1918 the field had produced more than 2,827,900,000 barrels of oil. The 

 largest well flowed for IS months, and is said to have produced more than 

 8,000,000 barrels of oil, with a maximum daily production of 05,000 barrels. 



Granitoid and metaraorphic rocks form the foundation upon w^hich rest 

 Tertiary and possibly some Cretaceous sediments. Structure is complex; 

 in the mountain regions the rocks are much folded and faulted, but in the 

 outermost foothills along the border of San Joaquin Valley the folds are 

 broad and open and extend from the main range into the valley. It is 

 about these obliquely trending folds that the petroleum has accumulated. 

 The petroleum is thought to have originated in a Miocene diatomaceous 

 shale, and has for the most part migrated and accumulated in the late Ter- 

 tiary sandy beds that imconformably overlie the shale. Barren beds are 

 found interspersed among the oil-bearing sands. Near the outcrop the 

 oil becomes viscous or tarry and seals the beds more or less completely. 

 In parts of the field where the oil is buried more than 2000 feet a zone of 

 tar-filled sand lies less than 1000 feet below the surface. Tliis zone is be- 

 lieved to mark the place where the upward-moving hydrocarbons have met 

 and been oxidized by surface v/aters. 



The paper includes descriptions of the individual areas with suggestions 

 for future work. J. D. Sears. 



GEOLOGY. — Geology and water resources of the Gila and San Carlos Valleys 



in the San Carlos Indian Reservation, Arizona. A. T. SchwEnnESEn. 



*U. S. Geol. Survey Water-Supplv Paper 450-A. Pp. 27 (1-27), pis. 



4, figs. 2. 1919. 



Most of the arable land in the valleys of Gila and San Carlos rivers, within 



the San Carlos Indian Reservation, Arizona, is undeveloped because of the 



inadequate supply of water for irrigation. The report deals with the physiog- 



