Brief Notices. 277 



In the same Jourcal, January 4, 1913, Dr. F. E. "Wright describes 

 a simple accessory to the vertical illuminator used in the micro- 

 scope, which enables the observer to produce apertures of any 

 desired size in any part of the field, and at the same time to eliminate 

 disturbing rays. 



2. In the American Journal of Science, 1913, vol. xxxv, 

 pp. 63-82, Dr. F. E. "Wright discusses the methods available for 

 producing oblique illumination in the petrological microscope, and 

 recommends the use of either a sliding stop in the lower focal plane 

 of the condenser, or placing the index finger below the condenser and 

 observing the edge of the shadow cast by it. He proceeds to consider 

 the utility of the method in the determination of relative refractive 

 indices, and points out that the interference phenomena between 

 crossed nicols in oblique illumination and in convergent light are 

 precisely similar. Incidentally he draws attention to a useful field 

 method of distinguishing between calcite and dolomite. The 

 powdered mineral is placed in a drop of monobromonaphthalene 

 between two glass slips and studied with a lens in oblique 

 illumination. In the case of calcite the grains have coloured fringes. 



3. In the Proceedings of the "United States National Museum, 

 vol. xliv, Mr. Gr. P. Merrill describes the meteoric stone found in 

 1911 near Cullison, Pratt County, Kansas, and said to have fallen 

 there on December 22, 1902. The mass, which weighs lO'lO kilo- 

 grams, is now in the United States i^ational Museum. It is so dense 

 and fine-grained that it resembles a weathered boulder of a trappean 

 rock, but an examination of a thin section at once revealed its true 

 character. The meteorite has an interesting chondritic structui'e, 

 and shows signs of brecciation. It probably formed part of a much 

 larger mass. 



4. Chilean Borate Deposits, — Mr. E. T. Chamberlin discusses 

 "The Physical Setting of the Chilean Borate Deposits" {Journ. 

 Geol., Chicago, xx, p. 763, Nov.-Dec, 1912). He points out 

 that throughout the extent of the great plateau, which rises from 

 12,000 to 13,000 feet above sea-level in Chile, Bolivia, and Peru, 

 there are numerous lakes, saline marshes, and beds of former lakes, 

 mostly with no outward drainage. The large lakes of Titicaca and 

 Pampa Aullagas are well known, but there are many minor lake-flats, 

 dry or nearly so, which escape notice. It is on some of these old 

 lake-bottoms that the great borate deposits of South America occur; 

 but it is significant that the lacustrine tracts which contain borax, 

 mostly lie close to the volcanoes of the Western Cordillera. Away 

 from the volcanoes, whether eastward over the central plateau, or 

 westward down the long desert-slopes leading towards the coast 

 where the nitrate beds abound, the borates rapidly disappear. They 

 thus seem to be related to the volcanoes. The nitrates occur on open 

 Salinas at less elevations, 3,000 to 5,000 feet. The borax fields are 

 located high up on the edge of the tableland close to the base of the 

 big volcanoes. Both nitrates and borates are dependent for their 

 accumulation and preservation upon the extreme aridity of the 

 region. 



