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University of California Publications in Geology [Vol. 8 



porphyry. The chalcocite has probably been deposited as a result of 

 the migratory descent of salts of copper from the gossan of an ore 

 body, now removed by erosion, in accordance with the principle of 

 diffusion. 32 The extent of these secondary deposits testifies to the 

 magnitude of the original deposit from which they were derived. In 

 my paper on these deposits I showed that "The dominant feature of 

 the Paleozoic rocks is a broad syncline, the axis of which runs nearly 

 north and south, through the Ruth mine, and pitches northerly at a 

 considerable angle. 33 I also called attention to the laccolithic character 

 of the porphyry and its relation to the syncline. 



' ' The porphyry belt lies transverse to a well-marked northerly pitching syn- 

 cline of the Euth limestone. On the south side of the porphyry belt different 

 stratigraphic horizons of the Ruth limestone abut upon it and the plane of 

 contact does not conform to the planes of stratification but in general appears 

 to dip under the porphyry. On the north side of the belt, the Ruth limestone 

 overlies the porphyry, dipping away from it but again meeting it at different 

 stratigraphic horizons. It is evident from this relationship not only that the 

 porphyry is intrusive in the Ruth limestone, but also that the intrusion occurred 

 subsequent to the establishment of the synclinal structure." 34 



These general relations are shown in the diagram, figure 3. Here 

 again we have an important deposit of copper ore genetically con- 

 nected with a laccolithic intrusion traversing a well-defined syncline; 

 and again the presumption is that the water contained in the strata 

 below the laccolith and that which would flow to the same region from 

 the limbs of the syncline wotdd tend to rise on the border of the 

 intrusion or through it after solidification, by any conduits that might 

 be supplied either by the intrusive act or by subsequent shrinkage. 

 Why should such waters be denied the function of dissolution under 

 the influence of high temperature and of deposition at cooler levels? 



Bisbee. — At Bisbee we have another instance of copper ores asso- 

 ciated with a small "stock" intrusive into a well-defined faulted 

 syncline, the general and detailed relations of which are well known 

 through the work of Ransome. 35 With apologies to the latter I take 

 liberty of reproducing in diagrammatic form (fig. 4) a portion of 



"-'See Bull. M. and M. Soc. Am., no. 23, May, 1910, pp. 263, 264; Penrose, 

 R. A. F., Jr., Certain phases of superficial diffusion of ore deposits, Econ. Geol., 

 vol. 9, no. 1, 1914; Lawson, A. O, Diffusion of ore deposits, Mining and Scientific 

 Press, July 4, 1914, p. 20. 



33 The copper deposits of the Robinson Mining District, Nevada, Univ. Calif. 

 Publ. Bull. Dept. Geol., vol. 4, no. 14, 1906, p. 297. 



si Op cit., p. 313. 



33 Ransome, F. L., The geology and ore deposits of the Bisbee quadrangle, 

 Arizona, U. S. G. S. Professional Paper no. 21, 1904. Also the Bisbee folio, 1904. 



