IRON MINE WORKINGS. 397 



Whether it will lead to more important developments in that direction 

 explorations have not yet been sufficiently extensive to determine. 



The main ore body on this line extends more or less continuously from 

 a little above the fifth level eastward to the bottom of the Tucson shaft, 

 being mainly concentrated between the fifth and eighth levels, where it 

 extended at times to a depth of 30 feet or more below the contact. A very 

 interesting feature of this remarkable ore body is the occurrence of a body 

 of Gray Porphyry, cutting up into the limestone and at one point reaching 

 the contact with the White Porphyry. It has no apparent connection with 

 the body already mentioned in the Main incline. At the time of examina- 

 tion it was so little explored that but little could be ascertained as to its 

 form or extent, and the representation given in Section A is almost entirely 

 ideal. It is there drawn as extending across the contact into the White 

 Porphyry, for the reason that Mr. Jacob found White Porphyry under it in 

 the old Tucson drift, where it runs above the North incline. Both north 

 and south of this line, however, it does not reach the contact, and ore and 

 vein material are continuous over it. Later developments have shown that 

 the ore extends to a considerable depth into the limestone along its contact 

 and that its general direction is northwest and southeast. 



It is probable that both these bodies of Gray Porphyry are irregular 

 offshoots from the main intrusive sheet at the base of the Blue Limestone 

 and differ from the ordinary dike. The fact that the one which crosses the 

 general direction of the ore bodies is accompanied by a concentration of 

 rich ore in its vicinity, while that which runs parallel with this direction is 

 not, is in accordance with the conditions found in connection with such 

 cross-cutting bodies of porphyry on Carbonate and Fryer Hills and with 

 the theory that they are favorable to the concentration of ore when so situ- 

 ated, in that they would produce a retardation in the flow of the ore solu- 

 tions and thus give them more time to deposit their load. 



It was in one of the drifts running north from the North incline, at the 

 sixth level, that a mass some two feet in diameter was found, composed 

 mainly of native sulphur associated with a little carbonate of lead. As it 



