SILVER AND GOLD, CONTINUED. 229 



Graham County contains the Clifton copper district, referred 

 to under Example 20. 



Cochise County is the southeastern county, and contains the 

 Tombstone district, the most productive of the precious metals in 

 the Territory. 



2.11.10. Tombstone. A great porphyry dike up to TO feet 

 wide, cutting folded Paleozoic strata, and itself extensively faulted 

 and altered, and carrying above the water line in numerous verti- 

 cal joints, or partings, quartz with free gold, horn silver, and a lit- 

 tle pyrite, galenite, and lead carbonate. Curiously enough, in the 

 porphyry itself, and far from the quartz veins, flakes and scales of 

 free gold have been found, evidently introduced in solution. Ore 

 also occurs along the side of the dike. There are also other fis- 

 sures parallel with this principal dike, and still another series 

 crossing these and the axis of the great anticline of the district. 

 Connected with these fissure veins are bedded deposits in the 

 limestone, along the bedding planes or dropping from one to an- 

 other, appearing to have originated by replacement. Blake offers 

 two explanations of the first-mentioned dike deposit either that 

 the dike itself held the precious metals, or that they came from the 

 pyrite of the adjoining strata. Several other mining districts of 

 less note occur in the county. The important copper deposits of the 

 Bisbee region have already been mentioned under Example 20/! 



2.11.11. Pima County is the central county of the southern 

 tier and has Tucson as its principal city. There are numbers of 

 mines of the precious metals, and a few less important copper de- 

 posits. 



Yuma County, in the southwestern corner, has some mines 

 along the Colorado River, on quartz veins in metamorphosed rocks, 

 containing silver and lead minerals. 1 



1 G. F. Becker, Tenth Census, Vol. XIII., p. 44. G. H. Birnie, " Castle 

 Dome District," Wheeler's Survey, 1876, p. 6. W. P. Blake, " The Geology 

 of Tombstone, Ariz.," M. E., X>-334, Engineering and Mining Jour- 

 nal, June 24, 1882, p. 328 ; The Silver King~Mine, a short monograph, 

 New Haven, March, 1883. Rec. See also Engineering and Mining Jour- 

 nal, April 28, 1883, p. 238, J. F. Blandy, "The Mining Region around 

 Presrott, Ariz.," M. E., XI. 286, Engineering and Mining Journal, July 

 21, 1883. " On Tombstone, Ariz.," Ibid., May 7, 1881, p. 316 ; March 18, 

 1882, p. 145. "Silver in Arizona," General Review, Engineering and Min- 

 ing Journal, Sept. 21 and 2$, 1880, pp. 172, 203. "Central Arizona," Ibid., 

 April 23, 1881, p. 285. O. Loew, "Hualapais District," Wheeler's Survey, 



