abstracts: geology 451 



have gone, though it seems to be less plentiful in the deeper parts of 

 the veins. 



Owing to the absence of silica and to the ease with which the carbo- 

 nate can be changed to an oxide, simple calcination being sufficient to 

 drive off the carbon dioxide, and to the comparative difficulty experi- 

 enced in decomposing the silicate, the rhodochrosite is by far the more 

 valuable as a source of the metal. Fairly pure rhodochrosite occurs in 

 several places. 



A reserve of not more than 2600 tons, as estimated, contains 40 per 

 cent or more manganese, and but little more than one-third of this 

 amount runs less than 10 per cent silica. In addition fairly detailed 

 estimates show totals of about 132,000 tons of material averaging 24 

 per cent manganese and 50 per cent silica and 270,000 tons averaging 

 11.5 per cent manganese and 73 per cent silica. Tests of the richer of 

 these two grades so far reported by the mining companies, though not 

 wholl}' satisfactory, by no means discourage the hope that it can be 

 profitably concentrated. 



R. W. Stone. 



GEOLOGY. — The coal fields of the United States. The coal fields of 

 Ohio. J. A. BowNOCKER, State Geologist. With a corn-puiation 

 of the original coal content of the fields. F. R. Clark. U. S. 

 Geol. Survey Prof. Paper 100-B. Pp. 62, with maps and sections. 

 1917. 

 A description of the occurrence, composition, and uses of Ohio coals, 

 with a bibliography; includes also an estimate of the original coal con- 

 tent of the Ohio fields. The principal part of the tonnage is contained 

 in seven coal beds. It is estimated that the total original tonnage of all 

 beds in all counties was 87,638,000,000 short tons, and that after deduct- 

 ing the quantity mined and wasted in mining, there remains available 

 86,552,000,000 short tons. 



R. W. Stone. 



GEOLOGY. — Geology and paleontology of the Raton Mesa and other 

 regions in Colorado and New Mexico. Willis T. Lee and F. 

 H. Knowlton. U. S. Geol. Survey Prof. Paper 101. Pp. 450. 

 1917. 

 The principal conclusions arrived at in this report are as follows : 

 The coal-bearing rocks of the Raton Mesa region, which have for- 

 merly been referred to the Laramie, constitute two distinct formations, 

 separated in time by a period of erosion. 



