Oct. 4, 1921 abstracts: geology 393 



GEOLOGY. — Some deposits of manganese ore in Colorado. Edward L. Jones, 

 Jr. U. S. Geol. Survey Bull. 715-D. Pp. 12. 1920. 



Many deposits of manganese ore in Colorado have been described by J. B. 

 Umpleby in 1917 and the Colorado Geological Survey in 1918. A number of 

 other localities were examined by the writer in 1917; these are located in 

 Gunnison, Hinsdale, Ouray, Dolores, Custer, and LaPlata Counties. 



Deposits of manganese ore in Colorado occur in sedimentary and igneous 

 rocks ranging in age from pre-Cambrian to Tertiary. They are found in 

 veins and brecciated zones; as replacement deposits; and as probably original 

 bedded deposits. The veins and brecciated zones constitute by far the most 

 numerous type of manganese deposits in Colorado, but economically they have 

 proved of little importance. Replacement deposits of manganese ores occur 

 principally in the oxidized parts of lead-silver deposits in the Leadville dis- 

 trict, and of deposits containing zinc and iron sulfides in the Red Cliff district. 

 A deposit of manganese ore which probably represents the oxidized and en- 

 riched part of an original sedimentary bed occurs in sandstone and shale in 

 western San Miguel County. The manganese ores are composed domi- 

 nantly of the oxides pyrolusite, manganite, psilomelane, and wad, generally 

 mixed with iron oxides. . J- D. Sears. 



GEOLOGY. — Deposits of iron ore near Stanford, Montana. L. G. Westgate. 

 U. S. Geol. Survey Bull. 715-F. Pp. 8, figs. 4. 1920. 



The iron ores known as the Running Wolf hematite deposits lie just within 

 the northern border of the Little Belt Mountains, in Cascade and Fergus 

 Counties, Montana. A great series of sedimentary rocks, ranging in age 

 from Algonkian to Cretaceous, rests unconformably upon Archean granite 

 and gneiss. The deposits occur in tabular bodies in the Madison limestone 

 (Carboniferous), at the contact with intrusive porphyry. The ore is a com- 

 pact gray or reddish-gray hematite, which contains in places enough magne- 

 tite to make it react to the magnet; it is not to any large degree limonitic at 

 the surface. 



Development work has not gone far enough to make possible any estimate 

 of the quantity of ore that can be mined, although several suggestive calcula- 

 tions are included in the paper.- At the surface the ore body is of varying 

 width, reaching a maximum of 50 feet. As it is a contact deposit in limestone, 

 it will vary in dimensions from place to place according to the character and 

 course of the solutions at work. The depth to which the ore extends below 

 the surface is unknown. J. D. Sears. 



GEOLOGY. — Phosphate rock near Maxville, Granite County, Montana. J. T. 

 Pardee. U. S. Geol. Survey Bull. 715-J. Pp. 5, pi. 1, fig. 1. 1921. 

 The phosphate bed and its inclosing rocks are bent into several parallel, 

 tightly squeezed folds that trend northward. The westernmost fold, a 

 large syncline, is partly overridden by a huge mass of rock brought by thrust 

 faulting from the west, and the strata that form the western limb of the syn- 

 cline appear as if overturned by a force acting from the west. East of the 

 syncline and beyond the area of the overthrust mass all the anticlines lean 

 to the west as if they had been pushed over by a force acting from the east. 

 Presumably the thrust acting from the west was the later. On the south 

 the folds are lost in areas of faulted and intrusive rocks, and on the north, 

 owing to a persistent pitch in that direction, they disappear beneath a cover 

 of later rocks. As a result of the structure and erosion combined, the out- 



