abstracts: engineering 15 



mately 15 miles long and 12 miles wide. The Basin is underlain domi- 

 nantly by the granite of the great Idaho batholith, which is believed 

 to be of late Cretaceous or early Tertiary age. During Tertiary time 

 most of the Basin was occupied by a lake, and deposits of clay, sand, 

 and gravel accumulated. Lava flows were erupted during and after 

 the deposition of the sediments. 



Since the discovery of gold in 1862, Boise Basin has produced over 

 $53,000,000 in precious metals. Of this amount the greater part was 

 obtained from placers, but since the depletion of the gravels the lode 

 deposits have been receiving more attention. The placer gold was 

 derived from the disintegration of veins that occur in a belt of porphyr- 

 itic dike rocks and in zones of shearing in the granite. The lodes 

 now being worked are chiefly valuable for their gold and silver content, 

 but with improved milling methods lead, copper, and zinc will probably 

 add materially to the output. Monazite occurs abundantly in the 

 placers but is not utilized. An unidentified radium-bearing mineral 

 was found in placer gravels at one locality. E. L. J., Jr. 



GEOLOGY. — Tin ore in northern Lander County, Nevada. Adolph 

 Knopf. U. S. Geological Survey Bulletin 640-G. Pp. 125-138. 

 1916. 

 Tin ore has recently been found in northern Lander County, Ne- 

 vada. The stanniferous mineral is exclusively wood tin, a form of 

 stannic oxide concentrically banded like exogenous wood. It occurs 

 in narrow veinlets traversing a series of rhyolite flows of middle Ter- 

 tiary age; in places the veinlets are sufficiently closely spaced to form 

 low grade lodes, but because of the small amount of development 

 work so far done not much is known of the persistence and tenor of 

 these lodes. The minerals associated with the wood tin are specular 

 hematite, lussatite (a fibrous form of silica resembling chalcedony), 

 chalcedony, tridymite, and opal. The deposits resemble closely those 

 of the Mexican states of Durango, Zacatecas, and Guanajuato, but the 

 association of wood tin with abundant tridymite and lussatite appears 

 to be distinctive of the Nevada occurrence. A. K. 



ENGINEERING.— Colorado River and its utilization. E. C. LaRtje. 



U. S. Geological Survey Water Supply Paper 395. Pp. 231, with 



25 plates and 5 figures. 1916. 

 The region traversed by the Colorado and its tributaries is one of 

 great interest in every respect. Various government bureaus have 

 investigated certain questions pertaining to the water resources of 



