GEOLOGY. 343 



jure its value, and prevent its reception at the mint on deposit. 



271. Other Metals. Copper ores are abundant in the 

 Colorado desert, but are of little value there, on account of 

 the high cost of reduction and transportation. Large deposits 

 of copper pyrites have been found in Calaveras, Fresno, El 

 Dorado, Amador, and Plumas Counties. 



Iron, in rich beds of hematite, magnetic, and other valuable 

 ores, exists in Calaveras, El Dorado, Sierra, and Plumas Coun- 

 ties. 



A vein of brown oxide of tin, containing 20 per cent, of 

 metal, and ten feet wide, has been opened at Temascal, San 

 Bernardino County ; but the extraction of it is not considered 

 profitable, so nothing is done with it, or with other similar 

 veins in the same county. 



272. Limestone. A remarkable belt of limestone runs 

 along the side of the Sierra Nevada, from the Bower Cave in 

 Mariposa County, to Oroville, a distance of 160 miles. Though 

 only a few hundred feet in thickness, it happens to include a 

 number of the richest placer mining camps in the State. 

 Among -these are Columbia, Springfield, Kincaid's Flat, 

 Murphy's, Volcano, and Indian Diggings. The limestone is a 

 coarse marble in general character, and where crossed by 

 streams, has been gullied out by numerous channels, leaving 

 pinnacles of rock with open spaces between them. These 

 spaces were filled with auriferous gravel, and were singularly 

 rich in gold. At a few points the marble is hard and suscep- 

 tible of a good polish. Metamorphic limestone exists at many 

 points in the coast mountains, the principal quarries being in 

 Santa Cruz and Contra Costa Counties. 



273. Coal. The old red sandstone and the " true car- 

 boniferous " rocks, as they are called, are wanting in Califor- 

 nia, and it was long supposed that no valuable coal would ever 

 be discovered in the State ; but some veins of a very good 

 quality have been found near Mount Diablo. The mineral 

 contains far more solid combustible matter, and less incombus- 



