150 EEPORT UNITED STATES GEOLOGICAL SUEVEY. 



Chalcedony. — Chalk Hills, eight miles south of Cheyenne Mountain ; 

 at the Los Pinos agency; on the bluff's near Wagon-Wheel Gap; 

 along the Upper Rio Grande Valley ; in Middle and South Parks ; 

 Buffalo Park; Fair Play; Frying Pan; Front Creek; Gunnison 

 River. Found frequently in drift accumulations. 

 Flmt. — Occurs together with chalcedony. Found very frequently 



in the lower members of the trachytic series. 

 Aventurine quartz. — On Elk Creek. 

 Ghrysopase. — Rare in Middle Park. 



(Jarnelian. — Middle and South Parks; Los Pinos agency. 

 Onyx. — Middle Park. 

 Sardonyx. — Middle Park. 



Basanite. — East of the salt-works in South Park. It is found, to- 

 gether with flint, in some of the trachytes. 

 Prase. — Middle Park. 



Jasper. — Green and red, station 33 of 1873. Yellow, red, brown, 

 and gray at the Los Pinos agency. Throughout Middle and South 

 Parks; along the Gunnison, Dakota group, Arkansas, Grand, 

 White, Animas, and other rivers in the drift. Occurs also in 

 some of the trachytes, mostly red, brown, and green. The best 

 locality for this horizon is at the junction of Lost Trail Creek and 

 the Rio Grande. 

 Siliceous sinter. — South Park. 

 Quicksilver. — See Mercury. 

 Ehodochrosite. — Sweet Home Mine, Park County, in very beautiful 



specimens; in the Diadem Mine. 

 Rhodonite. — Eureka Gulch, near Howardsville ; San Juan, 

 RiPiDOLiTB. — Trail Creek, Clear Creek County, Colorado. In the Little 



Giant lode, Arastra Gulch, and in the Crystal Lode, Silverton. 

 Roscolite. — A greenish mineral, intimately associated with quartz, 

 found at the Keystone and Mountain Lion Mines, in Boulder County. 

 Genth publishes an analysis,* with the following result : 



Per cent. 



Li O2 57.15 



AI2O3 19.94 



V2O., 8.44 



Mn O trace 



FeO 1 3.51 



MgO 2.87 



Lio O trace 



NajO 0.94 



K2O 8.11 



H2O not determined 



100. 96 

 RuTiLE, — On the TJte pass, occurring in quartz. 

 Sanidite. — Occurs throughout the trachorheites, sometimes in very 



handsome crystals. Wherever the trachytes have been reheated the 



sanidite is adularizing. 

 Sardonyx. — See Quartz. 

 SCHAPBACHITE. — Occurs near Georgetown. 

 ScHEELiTE. — Crystals are reported from some of the mines near Baker's 



Park. 

 SCHIRMERITE (Endlich). — Red Cloud and Cold Spring Mine, Gold Hill. 



Occurs also in the other telluride districts. A specimen from the Red 



Cloud furnished,t gold, 18.82 ; silver, 28.60 per cent. (See Petzite.) 



* Zeitschr. fiir Kryst. und Mia. P. Groth, vol. ii, No. 1, p. 11, 1877. 

 t Ktp. U. S. Geol. Surv., 1873, p. 354. 



