us 



REPORT UNITED STATES GEOLOGICAL SURVEY. 



Synopsis of the geological formations foun.^ in Colorado — Continued. 



Locality. 



(iunnisou River . 



Bear Cauon 



Little Thompson . 



Fossils. 



Inoceramus, Ostrea 

 lugubris, Prionocy- 

 das Wyomingensif!, 

 Scaphites Warren- 

 ana. I. problemati- 

 cus. 



Inoceramus 



Character of strata. 



Yellow, shaly saudstones, 

 changing higher up into 

 yellow and gray shales. 

 Farther up black shales, al- 

 ternating with brown ar- 

 gillaceous sandstones. 

 Shales near top. 



Thin, shaly limestones near 

 base. Higher up lime- 

 stone and shales with gyp- 

 sum. Partly arenaceous. 

 Three hundred feet of 

 dark gray, partly calcare- 

 ous shales. Kusty yellow 

 and brown sandstone on 

 top. 



(Section not complete.) 

 Lifiht gray, compact lime- 

 stones near base. Blue- 

 gray s h a<l y limestones 

 higher up, followed by 

 shaly, yellow limestones. 



Diminution of thickness from west to east is noticeable. 



Eio San Juan . 



"White Eirer . . 

 Animas Eiver. 



Junction of E i o s 

 Blanco and San Juan. 



Pagosa Springs 



Canyon City 



Bear Cauon .. 



Little Thompson 



Ostrea, Oryphcea 



Inoceramus, Ostrea.. 



Inoceramus . 



Inoceramus 



Inoceramus, Ostrea. 



Gray and yelliw shales with 

 blown sandstones toward 

 middle. Shales argilla- 

 ceous, arenaceous, and cal- 

 careous toward top. 



Dark gray shales. Sind- 

 stones, brown, argillaceous 

 near base and top. 



Dark gray, almost black 

 shales. Toward lop, thin 

 strata of yellow sandstones 

 and brown shales with coal- 

 beds. 



Dark gray, fossiliferous 

 shales at base. Yellow 

 sandstone interbedded 

 with thin strata of shale. 

 Grayish-brown and yel- 

 lowish shales. Yellow and 

 white sandstones. This 

 extraordinary widening is 

 probably local. 



Dark gray shales. Near the 

 middle thin laminated 

 sandstones. Sandstones 

 with carbonaceous shales 

 at top. 



Light yellow and gray shales. 

 Calcareous near top, with 

 white and yellow sand- 

 stones. 



Dark argillaceous shales, 

 growinglightertoward the 

 top. 



Fine black shales near the 

 base, followed by tbin beds 

 of crumbling sandstones. 

 Higher u'), black shales 

 again. Tbin, dark shales 

 and slates, with some beds 

 of limestone near top. 



A gradual thinning out of the strata can be observed as we proceed eastward. 



