62 



SCIENCE 



[N. S. Vol. XXXII. No. 810 



to the atmosphere by direct evaporation or 

 through plants. Here there is no leaching of even 

 the most soluble salts. Instead they accumulate 

 at or near the surface, forming the so-called 

 " alkali soils." The same process acting on rocks 

 instead of unconsolidated soils causes the surficial 

 accumulation of manganese, iron, etc., and the 

 formation of the " Schutzrinde " or " desert 

 varnish." 



Recent Experiments relating to the Transfer of 



Gold by Gold Dilute Mineral Waters: W. H. 



Emmons. 



The experiments which form the basis of this 

 paper were made by Mr. A. D. Brokaw at the 

 request of the speaker and by Mr. W. J. Mc- 

 (Jaughey and others. The experiments show that 

 with cold dilute solutions approximating in com- 

 position the average of many mine waters, there 

 is markedly great solvent action on gold when 

 manganese is present. The best available data 

 indicate that such solvent action is more than 

 250 times as great with solutions of manganitic 

 salts as with solutions of cuprie or ferric salts 

 of similar concentration. Conversely, it has also 

 been demonstrated experimentally that the pre- 

 cipitation of gold by ferrous sulphate is delayed 

 if manganitic salts are present in the solutions. 



It may be inferred from these experiments { 1 ) 

 that manganiferous gold ores should be more 

 extensively leached of their gold in the upper 

 portions of the lodes than deposits which do not 

 carry manganese, and as a consequence that rich 

 placers would be less likely to be associated with 

 manganiferous than with non-manganiferous gold 

 deposits; (2) that secondary enrichment in gold 

 would extend to greater depths in manganiferous 

 than in non-manganiferous lodes. 



Using Lindgren's classiiication of the gold de- 

 posits of North America, a study of the literature 

 was made to determine to what extent these con- 

 clusions were supported by field evidence. In 

 general those deposits in which it has been sup- 

 posed that gold was dissolved and reprecipitated 

 by cold meteoric waters are characterized by 

 manganiferous gangues. Nearly all of these are 

 of late Cretaceous or Tertiary age. 



Some Features of the Geology of the Navajo 



Reservation: H. E. Gbegdky. 



During the field season of 1909 a reconnaissance 

 survey was made of that portion of Arizona and 

 Utah between the Little Colorado and San Juan 

 rivers. The topographic expression of this region 

 is, in general, a plateau with an elevation of 



about 6,000 feet, reaching 10,400 feet at Navajo 

 Mountain and dropping to 5,000 feet at the north 

 and south where the Cretaceous beds have been 

 removed. With the exception of Chin Lee Valley 

 and the broad washes tributary to the Little 

 Colorado, the stream channels are deeply in- 

 trenched. This fact, together with the scarcity of 

 water and the occasional unfriendly attitude of 

 the Navajo and Pahute Indians, makes the coun-. 

 try somewhat difficult of access. 



The strata in general are horizontal, with the 

 exception of the monocline extending from Comb 

 wash to Marsh Pass, the anticlines cut by the 

 San Juan north of Monument Valley and the 

 Defiance fold with accompanying hogbacks. Rocks 

 of Triassic age are the most widely exposed, but 

 the Carboniferous is seen in the San Juan canyon; 

 the Moencopie (Permian?) covers considerable 

 areas; the Jurassic is believed to be represented; 

 the Cretaceous (Dakota and Colorado?) forms the 

 Zilh-le-jini Mesa, as well as the mountains along 

 the Arizona-New Mexico line; and the Tertiary 

 caps Choiska and possibly also Navajo Mountain. 

 The Moki Buttes south of Keams Canyon consist 

 of necks and lava-capped mesas, remnants of 

 flows of probably post-Pliocene time, which cov- 

 ered an area of approximately 600 square miles. 

 Necks and dikes of Jurassic rock, usually basalt 

 carrying peridote, are scattered irregularly over 

 the reservation. Parts of Tunitcha and Luka- 

 chuckai Mountain are capped by lava and the 

 Carriso Mountain is a mass of diorite of lacco- 

 lithic origin. 



The oil field twenty-five miles west of Bluff, 

 Utah, and the coal field at and to the north of the 

 Hopi villages are of commercial importance, but 

 there is little basis for the reports of gold and 

 silver deposits. Preliminary studies of this re- 

 gion indicate that by means of shallow and deep 

 rock wells water may be developed in sufficient 

 quantities to enable the Navajo, Pahute and Hopi 

 Indians to increase the size of their fiocks and 

 the number of small fields suitable for the growth 

 of corn. 



At the 233d meeting of the society, held on 

 Wednesday, May 11, 1910, the following papers 

 were read : 



Regular Program 

 The Composition of the Soil Solution: F. K. Cam- 



EKON. 



The soil solution is the result of geological 

 processes, and is the natural nutrient medium for 



