APRIL 19, 1921 abstracts: geology 193 



the sediments and granodiorite only a mile or so from the cinnabar prospects, 

 and numerous dikes and less regulai bodies of rhyolite porphyry intrude the 

 sediments and the granodiorite. The cinnabar deposits are in the limestones 

 or in the sediments immediately adjoining the limestones, and for the most 

 part thev are verv near the contact between the limestones and quartzites. 

 The ore bodies appear to be irregular lenses or chimneys of silicification in 

 the limestone, and the ore is in part the chaledonic silica and in part the 

 friable marble that adjoins the silica bodies. Cinnabar appears to be the 

 chief sulfide in the ore, but some pyrite is present and more may be found at 

 greater depth. Stibnite is present in the district and is associated with some 

 cinnabar, but it was not observed in the cinnabar ores. 



The district has not been sufficiently prospected to justify any definite 

 prediction as to the future outlook. E. S. L. 



GEOLOGY. — Coal in eastern Idaho. George R. Mansfield. U. S. Geol. 

 Survey Bull. 716-F. (Contribs. Econ. Geol., 1920, Part II.) Pp. 31 

 (123-153), pis. 2, figs. 3. 1920. 



Many of the so-called coal prospects are in phosphate rock that superficially 

 resembles coal and contains so much carbonaceous matter that upon distilla- 

 tion it yields small amounts of oil. Other supposed coal is obsidian. The 

 carbonaceous shales of the Wayan and Bear River formations of Lower 

 Cretaceous (?) and basal Upper Cretaceous age, respectively, though pros- 

 pected, have no commercial value. The only producing mines are in Horse- 

 shoe Creek on the west side of the Teton basin. Here the coal beds, tenta- 

 tively correlated with the coal-bearing Frontier formation (Upper Cretaceous) 

 of western Wyoming, lie near and east of a great thrust fault and may be 

 closely folded in a northward pitching syncline. The coal is bituminous and 

 of good quality. Large scale production is probably impracticable but im- 

 provements now in progress will probably make possible a greater annual 

 yield than formerly. A 32-inch coal bed of probably similar age and quality 

 occurs on the Continental Divide in Clark County. There is little chance of 

 finding other valuable coal-bearing areas in this region. A structure perhaps 

 fav^orable for the accumulation of oil is noted but its exploitation would be 

 hazardous. G. R. M. 



GEOLOGY. — Natural gas resources available to Dallas and other cities of 

 central north Texas. E. W. Shaw and P. L. Ports. U. S. Geol. Survey 

 Bull. 716-D. Pp. 35 (55-89), pis. 2, figs. 10. 1920. 



The bulletin presents the results of an investigation made on account of 

 shortage of gas in Dallas in the winter 1919-1920. Natural gas resources 

 within a circle of 300 mile radius around Dallas are deduced quantitatively 

 for the more developed fields from figures for the pore space and volume of 

 the gas-bearing sands and the pressure of the gas in them, with allowance 

 made for losses in extraction and delivery. Rough estimates based on general 

 experience and geologic conditions are made for other more or less developed 

 parts of the area. Especial attention is given to the Petrolia field; earlier 

 estimates by Shaw for this field are compared with present conditions and new 

 estimates are made. Water encroachment in this field is given particular- 

 consideration, and it is concluded that it is not taking place at random but 

 by creeping up the south flank of the dome. But as the rate of depletion of 

 gas far exceeds the rate of water encroachment, the future losses from the 

 latter cause will probably be slight. The bulletin contains a map showing 



