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flows have covered the region. Later erosion has partly uncovered the 
older sediments and intrusives. 
The ores are principally magnetite and hematite with a small amount 
of limonite, and occur (a) as fissure veins in the andesite, (b) as fissure 
veins and replacement deposits along the contact of the andesite and lime- 
stone, and (c) as a cement in a Cretaceous quartzite-breccia. 
ECE 
Geology of the Rangeley Oil District, Colorado, By Hoyt S, GALE, 
Bulletin 350, U. S. Geological Survey. 
A small field at the western border of Colorado is described where con- 
siderable prospecting for oil has been going on with some success. The 
rocks are principally Cretaceous and Tertiary. The base of the Wasatch 
formation (Tertiary) rests with apparent conformity upon the top of the 
Mesaverde formation (Cretaceous), but the absence of formations found 
between them elsewhere in Colorado indicates a non-conformity here. 
The structure is a quaquaversal fold with little evidence of faulting. The 
oil occurs presumably in lenses in the Mancos (Cretaceous) shale. 
JCal 
