90 Scientific Intelligence. 



6. Some Principles controlling Deposition of Ores ; by C. R, 

 Van Hise. Paper read before the American Institute of Mining 

 Engineers, February, 1900. Author's edition. — Prof. Van Hise 

 divides his paper into two parts, Part I being a consideration of 

 the principles governing ore deposition, while Part II treats of 

 their application to ore deposits. A brief outline of Part II fol- 

 lows. The outer zone of the lithosphere is a zone of fracture, a 

 zone where the rocks under stress break into fissures, etc. The 

 depth to which this zone extends depends upon the nature of the 

 rocks and other considerations, but in no case exceeds 12,000 

 meters. Below this depth we have a zone of flowage, where 

 rocks are deformed by flowage but do not fracture. The zone of 

 fracture below the level of ground- water is everywhere permeated 

 by water. This water is ever in more or less rapid circulation. 

 Below the zone of fracture there can be practically no circulation. 

 Therefore the first and fundamental premise of the paper is that the 

 greater number of ore deposits are the result of the work of under- 

 ground water. The second premise is that the material for ore 

 deposits is derived from rocks within the zone of fracture. The chief 

 cause of the circulation of underground water is gravimetric stress. 

 The water descends through the smaller openings in the rocks, 

 and continually seeking the easiest passages rises at last by means 

 of the main fissures. Descending waters are in the main agents 

 for solution ; the ascending waters are in the main agents for de- 

 position. After deposition, a second concentration and general 

 enrichment of the upper parts of ore deposits is caused by descend- 

 ing oxidizing waters from the surface. Ore deposits which have 

 their origin in deposition from solution may be of three kinds, 

 (1) deposited by ascending waters alone, (2) deposited by descend- 

 ing waters alone, (3) deposited by ascending waters and concen- 

 trated by descending waters. Deposits of the last class are by far 

 the most numerous. w. e. f. 



7. Physical Geography of the Texas Region; by Robert T. 

 Hill. U. S. Geological Survey, Physiographic Folio No. 3.— 

 The Physiographic folios " are designed chiefly as aids in the 

 teaching and study of physical geography. Folios Nos. 1 and 2 

 contain general illustrations and descriptions. The present folio 

 is descriptive of a large area which is particularly rich in dis- 

 tinctive physiographic types. The region is divided according 

 to its geographic features — soil, climate, geologic structure, drain- 

 age, underground water, and environment for human culture — 

 into six provinces. These provinces are described in detail, 

 with special reference to the large and small topographic fea- 

 tures represented. Plains are represented by the greatest 

 variety, and an unfamiliar type — "Bolson Plains" — has many 

 examples here. "Bolsons" are described as "apparently level 

 valleys inclosed by mountains, ordinarily without drainage out- 

 let — they are usually structural and floored with unconsolidated 

 sediments" (page 8). 



Ten sheets of "special illustrations" make the description* 



