abstracts: geology 209 



equal to about one-third the weight of the PbO; heated in a platinum 

 crucible in an electric furnace at 800° to form lead silicate glass; quickly- 

 raised to 1000° for a few minutes; cooled and weighed. O. A. 



PHYSICAL CHEMISTRY.— r/z^ term "inversion." J. B. Ferguson. 

 Science 50: 544-546. December 12, 19 19. 



The diversity among the phenomena which are referred to by the 

 name "inversion" is so great that at present the word has lost any pre- 

 cise meaning which it may have had in the past. In this paper the 

 suggestion is made that inorganic chemists confine the word inversion 

 to solid single-phase phenomena such as the change of rhombic to mono- 

 clinic sulfur, and the term transition to phenomena such as an incon- 

 gruent melting, instead of the present synonymous use of these terms 

 for all these phenomena. J. B. F. 



GEOLOGY. — Artesian waters in the vicinity of the Black Hills, South 

 Dakota. N. H. Darton. U. S. Geol. Survey, Water-Supply 

 Paper 428. Pp. 64, pis. 13, figs. 11. 1918. 



In the arid plains surrounding the Black Hills of South Dakota the 

 matter of water supply is one of the most important questions. Sur- 

 face waters in streams, springs, and shallow wells are meager in volume, 

 and in most places considerably mineralized. Fortunately the area is 

 underlain by water-bearing sandstones which receive water at their 

 outcrops in the Black Hills and will yield it when tapped by wells. 

 In order to ascertain the position of these sandstones and to delimit 

 the area of flow the geology of the region has been studied in considerable 

 detail, and the results are set forth in this report. The general structure 

 is a monocline dipping away from the Black Hills, and the water-bear- 

 ing Dakota, Lakota, Minnelusa, and Deadwood sandstones lie at vari- 

 ous distances beneath the surface of the plains. The stratigraphy of the 

 various formations from Cambrian to Tertiary is described in consider- 

 able detail, and in maps and cross-sections the underground relations 

 of the water-bearing sandstones are indicated. An account is given 

 of all deep wells and borings in the region, and a resum^ is presented 

 as to the conditions and prospects in the various districts. N. H. D. 



