abstracts: mineralogy 267 



United States; (4) ores worked primarily for copper; (5) titaniferous 

 iron ores. Most of the ores occur as veins, as a rule steeply dipping, 

 which arc in part fissure fillings and in part replacements of various 

 rocks along zones of fracturing. All the ores of the region are believed 

 to be genetically connected with the Tertiary (?) intrusive rocks. 



Enrichment in the Central City region has been confined mainly to 

 the class of gold-silver ores. Enrichment in gold appears to be con- 

 fined almost exclusively to portions of the ore deposits above or im- 

 mediately below the ground- water level. Silver enrichment is con- 

 fined to the ground-water zone. Enrichment in copper is nowhere 

 conspicuous. R. W. S. 



GEOLOGY. — Brachyceratops, a ceratopsian dinosaur from the Two 

 Medicine formation of Montana, with notes on associated fossil rep- 

 tiles. Charles W. Gilmore. U. S. Geological Survey Profes- 

 sional Paper 103. Pp. 44, with 4 plates and 57 figures. 1917. 



This paper gives as complete and detailed a description of the skele- 

 tal anatomy of Brachyceratops montanensis as the material at hand 

 will permit, and discusses briefly in systematic order other forms rep- 

 resented by specimens in the collection made in 1913 on the Black- 

 feet Indian Reservation. 



The stratigraphy of the Two Medicine formation is discussed by 

 Eugene Stebinger. Vertebrate fossils are found throughout the upper 

 part of the Two Medicine formation and nearly all of them belong to 

 the class Reptilia. The great number of trachodonts found appears 

 to indicate that these were the most abundant dinosaurs of the epoch. 

 Next to the Trachodontidae, the Ceratopsidae were most abundant. 



Fragments of turtles are plentiful; a few teeth and single bones of 

 extinct crocodiles, and isolated scales and plates of ganoid fishes were 

 found. The vertebrate fauna of the Two Medicine formation, as 

 represented by this small collection, although too meager to serve as 

 a basis for close comparisons with related faunas, accords with the 

 stratigraphic evidence for the correlation of the upper part of the Two 

 Medicine formation with the dinosaur-bearing beds of the Judith 

 River and Belly River formations. R. W. S. 



MINERALOGY. — Notes on alunite, psilomelanite, and titanite. Edgar 

 T. Wherry. Proc. U. S. Nat. Mus., 51: 81-88. 1916. 

 Includes descriptions with analyses and discussions of the com- 

 position of two specimens of alunite, one of psilomelanite, and one of 

 titanite. E. T. W. 



