1880. ] Geology and Palecntology. 54! 
Tue GEoLocy oF SOUTHERN Arizona.—Prof. E. T. Cox writes 
us from Tucson, Arizona, as follows; The oldest sedimentary 
rocks that I have seen in this part of the Territory are limestones, 
that contain fossils in the same layer, of coal measure, Sub-car- 
boniferous, and Devonian species: Productus cora, P. semireticu- 
latus, Spirifer lateralis? Zaphrentis sp.? Atrypa reticularis, and 
Fleliophyllum halli? I am inclined to place the entire limestone 
group as Sub-carboniferous. The rock is, wherever seen, semi- 
crystalline, and the fossils are very imperfect and few in number. 
The oldest and most persistent crystalline rock is coarse grained 
granite, which is readily disintegrated by atmospheric influences, 
and the débris mixed with fragments of the superimposed serpen- 
tine trap, basalt, porphyry, and ttachites, form the mesa and valley 
lands of the country, and gives rise to a remarkable topography. 
The mountains are in low, short and narrow ranges, that seem to 
rise from the intervening mesas, like islands in an ocean. Where 
porphyry or green stone form the principal mountain rocks, they 
are traversed in all directions by quartz lodes or veins, that pre- 
sent bold crops, and in very many instances may be traced for 
mineralizer, and we generally find in it, pockets of the richest 
Ores, assaying from $200 to $10,000 and more, in gold and silver, 
per ton of 2000 pounds. In localities where limestone forms the 
prevailing mountain rock, we find numerous and rich deposits of 
carbonate and sulphurets of copper, cupriferous silver, argentif- 
erous galenite and cerrusite. All the important copper and lead 
ores that I know of, in Pima county, are found in the sub-carbon- 
ee limestone or at the junction of the latter with crystalline 
rocks 
The cone-shaped mountains are capped with trachite, which 
alternates with basalt and trap, and sometimes an amygdaloid- 
like stone, always honeycombed, as though the once imbedded 
crystals had weathered out. You will also find on such mountains 
large beds of calcareous tufa, though not a trace of water can now 
be found anywhere in the vicinity, evidences of springs long since 
dr ied up. On the desert Mesas, between here and Yuma, I find 
imbedded in the sand and granite gravel, and forming a solid in- 
laid pavement, perfectly smooth pebbles of trap and basalt, that are 
polished as smooth as glass, are as black as tar, and glisten as 
though they had been japanned. Though all are finely glazed, 
some are covered with little pits. The polishing is done by the 
