GEOLOGICAL SURVEY OF THE TEREITORIES. 205 



1. Smoky quartz and black quartz. — Elk Creek. 



2. Rock or Berg crystal. — Near " Dirty woman's Eanch," and in geodes 

 in various mines. 



3. Rose quartz. — Quartz Hill. 



4. Agate, (moss agate, &c.) — Middle Park, Arkansas Eiver Park, &c. 



5. Amethyst.— Nevada City, Mill City, &c. 



6. Aventarine. — Elk Creek. 



7. Heliotrope, (bloodstone.) — Middle Park. 



9. Carnelian. — South Park and Middle Park. 

 ] 0. Chalcedony. — South Park, Trout (^reek Pass, &c. 



11. Ohrysoprase. — Middle Park. 



12. Jasi)er.— South and Middle Parks. 



13. Onyx. — Middle Park, Grand Eiver, &c. 



14. Sardonyx. — Golden City, Mount Vernon. 



Hornstoue, flint, milk quartz, prase, catseye, firestoue, and other 

 differont varieties of silicic acid, are met with in the above localities, but 

 have no especial interest. 



0/9fl/, (hydrated silicic acid.) — Idaho City, Golden City, South Boul- 

 der, &c. 



Feldspar. — Yery abundant in the mountains and as boulders and 

 X)ebbles throughout the Territory. Associated with quartz in the granites, 

 gneisses, and porphyries of the gold-bearing mountains. 



a. Orthoclase (AI2O3 . 3Si03 + KO.SiOa) is largely the predominant 

 feldsx>ar in the rocks of Colorado. 



a 1. Pegmatolite. — Flesh-red, orthoclastic, abundant as pebbles, scat- 

 tered with quartz over the jirairies for hundreds of miles. Eorms red 

 granites and gneisses with quartz and mica, and red sj^ enites with horn- 

 blende. Yery common. 



a 2. Adularia. — Forms a white porphyry vfhen associated with quartz 

 in many places along Fall Eiver, and in many veins. jSTot common. 



a 3. Sanidin. — Fine crystals of hopper-shaped sanidin from Quartz Hill. 



J). Plagioclastic feldspars. 



1) 1. Albite, (AI2O3 . sSiOs -f NaO . SiOs-j—Trouf Creek Pass. 



h 2. Oligoclase.^Arkansas Eive? Park, &c. 



h 3. Labrador, (AI2O3 . Si03 + CaO . SiOs.) — In thebasalts and diabases 

 of the region about the Spanish Peaks, Trinidad, the upi)er part of San 

 Luis Park, and the Puntia Pass. 



Hornblende, (silicate of lime, magnesia, and suboxide of iron). — In the 

 syenite in and around Idaho. 



Biorite. — Near Empire City and elsewhere. 



Garnet. — South Park, twenty miles from Fairplay. Breckeuridge. 



Mica, (KO . Si03 + AI3O3 . SiO^ + EO . SiO..) 



1. Potash mica. — Light colored. Frequent in the gneisses of Gilpiu 

 and other counties. 



2. Magnesian mica. — Dark colored. Frequent in the gneisses of South 

 Park, Trout Creek Pass, &c. 



LeiLcUe, (AI2O3 . SiOs + KO . SiOo.) — In trachytic lava between the 

 Cuchara and the Apish j)a. 



Chlorite. — In diabase, near Trinidad. 



AonpJdbole, (augite). — In basalts, near Trinidad, and diabase near 

 Apishpa. 



Upidote, (CaO . SiOs + [AI2O3 + FcaOs] SiOs.)— Trail Creek. 



To mmaHne. — Guy Hill. 



Calc spar, (CaO . C02.) — Yery widely distributed. Idaho, &c., &c. 



Gypsum, (CaO . SO3 -f HO.) — Interstratified in the new red sandstone 



