REVIEWS 649 



Pennsylvanian, Triassic (or Jurassic), and Comanchean rocks. These 

 are mostly limestones, though the early Mesozoic is marked by porphy- 

 ritic intrusions and the lower part of the Cambrian series is quartzitic. 

 The manganese ore, largely psilomelane, occurs in irregular bodies in 

 close association with fissures in the Carboniferous limestones; the 

 deposits follow the fissures, or extend laterally from them along certain 

 beds of limestone; they seldom descend to depths greater than fifty 

 feet and are worked by open cuts or shallow inclines. With the hard 

 psilomelane are lesser amounts of barite, quartz, a green copper-arsenic 

 compound (new species), and soft black pyrolusite; chalcolite is 

 occasional. 



In the Tombstone district the manganese grades into ores rich in the 

 precious metals; it occurs in irregular pipelike masses or chimneys 

 distributed along fault zones. 



Almost certainly these manganese deposits are related to the copper 

 ores, as they are generally closely associated. The manganese ores are 

 unquestionably supergene, being generally found only in the oxidized 

 zone. Psilomelane deposition seems to have been conditioned chiefly 

 by fissuring. In the Tombstone district, manganese-silver ores are as 

 common as manganese-copper ores in the Bisbee region, and possibly 

 the manganese zone here represents a leached silver zone. The deposits, 

 on account of their irregularity, can only be worked under unusual 

 conditions. Possibly not more than 60,000 tons of 40 per cent ore are 

 available in these two districts combined. 



Elsewhere in the state, in Coconino, Graham, Greenlee, Maricopa, 

 Mohave, Pinal, Santa Cruz, Yavapai, and Yuma counties, there are 

 smaller manganese deposits. Here veins, brecciated zones, bedded 

 deposits, and irregular deposits with travertine, all furnish greater or 

 lesser amounts of manganese ores. The ores are in pre-Cambrian 

 granites and gneisses. Tertiary rhyolites, andesites, and dacites, and 

 Quaternary basalts, as well as in limestones and quartzites of Paleozoic 

 age, sandstones of Tertiary age and course elastics of the Quaternary. 

 The manganiferous silver veins occupy an important place among the 

 vein deposits; they are well shown in the Hartshell shear zone ores and 

 in the Globe district; in such cases the manganese oxides are psilomelane, 

 pyrolusite, braunite, manganite, and wad. There may be more or less 

 iron oxide associated, as in the Globe district, where the ores are intimate 

 mixtures of manganese- and iron-oxides. Where braunite is the chief 

 ore mineral, it is commonly associated with cerusite, vanadinite, and 

 wulfenite. 



