SEPT. 19, 1921 abstracts: geology 373 



of akermanite, the component of lower melting-point, at a composition of 

 about 74 per cent Akermanite and 26 per cent gehlenite. 



The densities of crystals and glasses of akermanite, gehlenite, and several 

 intermediate mixtures were determined and found to confirm the isomor- 

 phous character of the system. Akermanite was found to show the unusual 

 feature of its glass having a greater density than the corresponding crystals 

 at 25° C. This peculiar character is checked by the indices of refraction 

 for glass and crystal, respectively, the index of refraction of the glass being 

 greater than the maximum index of the crystal. 



The optical characters of the crystals are a continuous function of the 

 composition. In optical characters akermanite is positive and gehlenite 

 is negative. Crystals of certain intermediate compositions are isotropic 

 for light of a definite wave length and constitute a transition phase between 

 positive and negative crystals. J. B. F. 



GEOLOGY.- — Mining in the Matanuska coal field and the Willow Creek dis- 

 trict, Alaska. Theodore Chapin. U. S. Geol. Survey Bull. 712-E. Pp. 

 46(131-76). 1920. 

 This report describes developments in the Matanuska coal field up to the 

 end of 1918 and records some recently acquired knowledge of the structure 

 and stratigraphy of the coal-bearing rocks and the character and persistence 

 of the coal beds, details of which are becoming more apparent with the open- 

 ing of the underground workings. The areal distribution, character, chemical 

 analysis, steaming and coking quahty of the coal are discussed, stratigraphy 

 and structure of the region are described, and the mining developments 

 depicted. R. W. Stone. 



GEOLOGY.— Mmmg in northwestern Alaska. S. H. Cathcart. U. S. 

 Geol. Survey Bull. 712-G. Pp. 14(185-98). 1920. 

 Discusses the adverse conditions which caused greatly decreased mineral 

 production in Seward Peninsula in 1918; describes the use of cold water in 

 thawing perpetually frozen muck and gravel and its application to placer 

 mining. Tungsten and platinum were produced, but wholly incident to 

 the mining of placer gold. A small quantity of coal was mined, and drilling 

 for oil in a locality where the hard rocks are granite and schist was unsuccess- 

 ful. R. W. Stone. 



GEOLOGY.— r/ie Mogollon district, New Mexico. Henry G. Ferguson. 

 U. S. Geol. Survey Bull. 715-L. Pp. 34(171-204). 1921. 



The Mogollon or Cooney district is in the southwestern part of Socorro 

 Coimty, New Mexico, about 14 miles from the Arizona line. The rocks 

 of the district are nearly all lavas, or sedimentary rocks composed of materials 

 derived from lavas. Flows of rhyolite and andesite, together with sedimen- 

 tary and pyroclastic rocks, had reached a total thickness of several thousand 

 feet when faulting of considerable magnitude took place and the region was 

 broken up into irregular blocks bounded by normal faults. The faulting 

 was closely followed by the introduction of mineral-bearing solutions, which 

 followed channels determined by the previous faulting, so that practically 

 all the faults are the sites of veins. 



The ores of the district are valuable mainly for silver. Argentite, pyrite, 

 bomite, chalcopyrite, and tetrahedrite, together with small amounts of horn 

 silver and native silver, are the principal ore minerals. The ores are princi- 

 pally sulfides and give evidence of being in part due to enrichment, although 



