proceedings: geological society 199 



THE GEOLOGICAL SOCIETY OF WASHINGTON 



The 264th meeting was held in the Cosmos Club, January 22, 1913, 

 at which the following communications were presented: 



A fall of volcanic ash at Juneau, Alaska in July, 1912: R. H. Chapman. 

 Parts of a letter from Benj. D. Stewart, dated July 28, 1912, were read, 

 giving a description of a fall of volcanic ash due to the eruption of Mount 

 Katmai. 



A sectarian fro7n New Mexico: W. T. Lee. 



The habitat of the Cambrian brachiopoda: Lancaster D. Burling. 

 A study of the Cambrian and Lower Ordovician, nearly 1200 localities, 

 represented in the United States National Museum shows: (1) that from 

 about 72 per cent of the localities brachiopods have been identified; (2) 

 that, dividing the sediments into three groups, shale, sandstone, and 

 limestone, 60 per cent of the genera and 85 per cent of the species have 

 been identified from but one type of sediment; and (3) that, after divid- 

 ing the localities into three groups, figures are obtained for each of the 

 groups, indicating that the number of species per locality is smaller in 

 shale than in sandstone and greatest in limestone. The accordance of 

 the results seems to justify the conclusion that habitat influenced not 

 only the nature but the number of species which are to be found in any 

 particular locality. 



The relations of ilmenite to magnetite in titaniferous magnetite. (Illus- 

 trated): Joseph T. Singewald, Jr. Experiments that have been con- 

 ducted in the magnetic separation of merchantable iron ore from titani- 

 ferous magnetite have yielded varying result, but in all cases only a 

 partial elimination of titanium, and a study of the ores to show their 

 mode of combination was undertaken. The problem was easily 'solved 

 by the study of etched polished sections of the ores in reflected light. 

 Ilmenite is unaffected by hydrochloric acid; whereas, magnetite is 

 readily acted on, and etches to a dull black surface. On examining the 

 etched specimens it is at once apparent that they consist of granular 

 aggregates of ilmenite and magnetite. The magnetite grains are not 

 homogeneous but contain minute intergrowths of ilmenite. These inter- 

 growl^hs are in part irregularly disseminated through the magnetite and 

 in part regularly intergrown with definite crystallographic orientation. 



Construction of a structure map of the northern anthracite field: N. H. 

 Darton. The map showing the structure of the northern anthracite 

 coal basin has been under construction for several years and is now nearly 

 ready for publication. It was prepared incidentally in connection with 

 a study of the origin of methane in coal, for the Bureau of Mines. The 

 northern anthracite basin was one of the areas selected and as one 

 branch of the inquiry was to ascertain the relation and the occurrence 

 of methane to the deformation of the beds the structure had to be plotted 

 in detail in various parts of the area. The data given on the large scale 

 mine maps, were utilized as far as practicable but in areas not reached by 

 mining the structure was determined from surface dips aided by num- 

 erous bore hole records. The horizon selected for contouring was the 

 lowest notable coal bed (Dunmore — Red Ash) and its configuration is 



