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University of California Publications in Geology [Vol.8 



his Bisbee special map, simplified so as to bring out the essential 

 structural features. As this is without doubt one of the important 

 localities in the southwest which Professor Lindgren kindly advised 

 me to study, I may say that I am not unfamiliar with it, and that I 

 agree with my distinguished critic as to the value of the suggestion 

 and instruction which it affords, particularly, of course, in the light 

 of Ransome's studies. Here an open syncline of Paleozoic strata has 

 been faulted down against the pre-Cambrian by the Dividend fault. 

 A "stock" of granite porphyry has invaded the country following a 

 portion of the fault fissure and displacing both Paleozoic and pre- 

 Cambrian rocks. The strata of the syncline abut upon the fault and 

 stock. The copper ores occur in the Paleozoic strata, principally in 

 Mississippian limestone in the vicinity of the stock and fault. Their 

 genetic relation to the intrusive body is unquestioned. Yet Ransome 

 does not find any very convincing evidence of their deposition by 

 magmatic waters. I call Professor Lindgren 's attention to the follow- 

 ing passages from the Bisbee monograph : 



' ' The objection to regarding- the metamorphism and mineralization as an 

 ordinary case of contact action is twofold. The stock itself has been thoroughly 

 altered and mineralized and could not have originally supplied from its own 

 mass the large quantities of magnesia and sulfid of iron and other constituents 

 introduced into the adjacent limestones. The greater part at least of the 

 mineralization must have taken place after the porphyry had solidified. It is 

 probable, although perhaps not in this case susceptible of definite proof, that the 

 mineralization and metamorphism were affected by heated aqueous solutions. 



' ' It is pertinent at this point to recall the general geological structure of the 

 rocks in which the ores occur. The limestones have already been described as 

 forming part of a syncline. They dip toward the Dividend fault and toward the 

 porphyry mass of Sacramento Hill. The inclination of the beds is such that 

 any waters sinking into the limestones through a radius of 7000 or 8000 feet 

 from the summit of Sacramento Hill and within an arc of nearly 90°, measured 

 southwesterly from the Dividend fault, would, if they moved along the concave 

 surfaces of the various beds, find their way downward to the Dividend fault 

 and to the contact with the porphyry stock. Water moving along the lower 

 beds, say at the base of the Abrigo limestone, would reach the Dividend fault 

 and the porphyry at a depth of over 1000 feet below the deepest ore bodies now 

 known. It would then tend either to rise, by hydrostatic pressure along the 

 Dividend fault and the contact with porphyry, or it would tend to sink deeper 

 into the earth along these structures. Whether it would follow either or both 

 of these courses would depend upon the adjustment of a number of factors, such 

 as hydrostatic head, volume of flow, relative size of channels, and difference 

 of temperature. If the porphyry mass still retained a part of its original heat 

 of intrusion, the waters would have some of this heat imparted to them and 

 tend to rise. If in addition, solutions, presumably heated, were rising from 

 depths below the bottom of the Paleozoic syncline through the Dividend fault 



