572 



APPENDIX. 

 Generalized Section for Southwestern Colorado. 1 



Names of Formations. 



Thickness 

 in Feet. 



Characteristics. 



Potosi volcanic series. 



1250 



- Unconformity-^^ 



•>- Unconformity ^ 



Burns latite. 



■">- Unconformity ~* 

 Eureka rhyolite. 

 ^ Unconformity "^ 

 Picayune andesite. 

 ~~- Unconformity-^^- 



San Juan tuff. 



^~~ Unconformity^-^ 



Telluride conglomerate . 



-~ Unconformity ~~~^ 



Cutler formation. 



Alternating rhyolite and quartz-latite flows 

 and tuffs, flows predominating near base. 

 Some thin upper flows in Potosi Peak are 

 glassy. 



Andesite flows, tuffs, and dikes, with both 

 augite and hypersthene. 



Flows, tuffs, breccias, and dikes of dark horn- 

 blendic quartz-bearing latite of andesitic 

 habit. 



Massive flows, dikes, and bedded tuffs, 

 former greatly predominating. 



the 



100-2000 



0-200 



1000 + 



Augite-andesite tuff, breccia, or agglomerate, 

 and massive flows. Base not known. 



Almost exclusively andesitic debris. Well 

 stratified near base, coarser and less dis- 

 tinctly bedded above. No fossils known. 



Contains pebbles and bowlders of schist, gran- 

 ite, and quartzite, with some Paleozoic lime- 

 stones and other sediments. Thickens 

 westward to 1000 feet, and here includes 

 sandstones and shales. 



Bright-red sandstones and pinkish grits and 

 conglomerates, alternating with reddish 

 sandy shales and limestones. 



Rico formation. 



300 



Dark red-brown sandstone and pink grits, with 

 intercalated greenish or reddish shale, and 

 sandy, fossiliferous limestone. 



Hermosa formation. 



2000 



Limestones, grits, sandstones, and shales. 

 Heavy bedded limestone predominates in 

 middle and upper parts, sandstone and shale 

 below. Fossils numerous. 



Molas formation. 

 ' — Unconformity - 



75 



Red calcareous shale and sandstone, with thin, 

 fossiliferous limestone lenses, and chert, 

 limestone, and quartzite pebbles. 



1 Cross and Howe, Silverton folio, U. S. Geol. Surv. 



