REVIEWS 409 



or more stratigraphic breaks may be present, the beds show no angular 

 unconformity." An unconformity is probable between the Devonian 

 and Mississippian portions of the Ouray. 



Pronounced folding and faulting occurred in post-Kangaroo (Permo- 

 Pennsylvanian( ?)) time. 



The primary ore minerals of the Monarch and Tomichi districts are 

 believed to be genetically related to the quartz monzonite intrusion. 



The principal ores produced in the Monarch district are of lead, silver, 

 gold, copper, and zinc. They occur as replacements in limestone and 

 dolomite, filling of fault fissures in limestone and quartzite, fissure veins 

 in igneous rocks, contact deposits, and as deposits in pegmatite, gneisss, 

 and schist. Further development is encouraged. 



The silver-lead ores now mined in the Tomichi district are chiefly 

 sulphide ores. The iron ore bodies are of magnetite and limonite. The 

 ores occur as replacements in limestone and dolomite, contact deposits, 

 fissure veins, and as bog iron deposits. The future of the district lies 

 in "the development of claims in groups." 



Detailed descriptions of the mines of both districts are given. 



V. O. T. 



Reconnaissance of the Geology of the Rabbit Ears Region, Routt, 

 Grand and Jackson Counties, Colorado. By F. F. Grout, 

 P. G. Worcester, and Junius Henderson. Bull. Colo. 

 Geol. Surv. No. 5, Part 1, 1913. Pp. 57, pi. 1. 



The Rabbit Ears region includes about 212 square miles in Routt, 

 Grand, and Jackson counties, Colorado, "along and near the west end 

 of the Rabbit Ears Range." 



The geological sequence is as follows: Archean gneisses, schists, and 

 granites; Permian or possibly Triassic "Red Beds"; the Upper Jurassic 

 or Lower Cretaceous Morrison formation; the Cretaceous Dakota(?), 

 Benton, Niobrara, and Pierre formations; early Eocene coal-bearing 

 beds; post-Eocene volcanic breccia, dikes, and sheets; Pleistocene and 

 Recent deposits. 



Unconformities occur between the Archean and the "Red Beds," 

 the "Red Beds" and the Morrison, probably between the Morrison and 

 the Dakota(?), the Pierre and the early Eocene coal-bearing beds, and 

 the coal-bearing beds and later deposits. 



Folding "began at or just after the close of Cretaceous time, probably 

 continuing for some time into the Tertiary " It is "probable 



