3l8 ABSTRACTS: GEOLOGY 



some veins, for every vein must finally end in depth as well as laterally; 

 in many veins change in wall rock has been at least a contributing factor. 

 The veins developed by other deep workings are heavily mineralized 

 and of high grade, and the geologic evidence is favorable to the per- 

 sistence of rich primary silver ores to depths considerably greater than 

 those yet attained in the mining operations. 



Although hot ascending waters are encountered in a number of the 

 deeper workings, there is little evidence that these waters are now de- 

 positing ores. R. W. Stone. 



GEOLOGY. — Coal south of Mancos, Montezuma County, Colorado. 

 A. J. Collier. U. S. Geol. Survey Bull. 691 -K. i6 plates, 2 

 figs. 1919. 



There are two coal-bearing formations near Mancos, Colorado, the 

 Dakota sandstone, in the lowlands north of the town, which yields a very 

 impure coal of bituminous rank, and the middle formation of the Mesa- 

 verde group which yields a coal of somewhat lower rank than the Dakota 

 coal, though relatively pure and much esteemed as a fuel. 



The formations have a uniformly low dip to the south. The coal 

 beds here described are all in the Menefee formation, are bituminous and 

 are nearly all less than 6 feet thick. Three mines supply local demand. 



R. W. Stone. 



GEOLOGY. — Geology of the Lost Creek coal field, Morgan County, Utah. 

 Frank R. Clark. U. S. Geol. Survey Bull. 691-L. Pp. 311- 

 322, I plate, I fig. 1918. 



The Lost Creek coal field lies in Morgan County, Utah, about lo or 

 12 miles northeast of Devil's Slide Station, on the main line of the Union 

 Pacific Railroad. 



The coal bed, which is lenticular and varies greatly in thickness even 

 in small areas, is confined to one coal-bearing zone. It is sub-bitumi- 

 nous and contains much moisture and many impurities in the form of 

 small lenses or partings of bone and shale. 



The rocks exposed in this field comprise two formations which differ 

 widely in character as well as in age; the older formation is of Jurassic 

 age and the younger of Tertiary age (Wasatch formation). These 

 formations are separated by a great unconformity representing a long 

 interval of time during which the older rocks were minutely folded and 

 the folds were later truncated by erosion. The rocks that are here 

 assigned to the Jurassic consist of limestone, shale, and well-indurated 

 sandstone. 



