24 STUDIES IN GEOLOGY, No. i 



ratic beds are nearly all gray. All copper-stained horizons 

 are in sandy beds, never in the shales; and they range over 

 a stratigraphic thickness of mo m. from the fault. 



Another section of the Vetas formation was measured, by 

 pacing and by tying in to locations on the map, along the 

 Pontezuelo River, 5 km. northwest of Corocoro beginning 

 at the Corocoro fault oft the north side of the river and 

 following the river to a point which included 1058 m. of 

 strata. The position of this section is shown on the map. 

 It likewise represents only a part of the formation, not 

 including the underlying beds that have been cut off by 

 the fault, nor a great thickness of overlying beds that 

 continue a long distance westward from the top of the 

 section. Of the total measured thickness of 1058 m., only 

 534 m. was measured in detail. The description of the 

 rest of the section, 239 m. at the base and 270 m. at the 

 top, is generalized. 



SECTION OF PART OF VETAS FORMATION 



ALONG PONTEZUELO RIVER 

 Meters 



At top i meter of thin-bedded sandstone, cupriferous and 



with plants 



58.00 Gray and tan sandstones and conglomerates predominate 

 26.00 Gray and tan sandstones and conglomerates predominate 



Two copper horizons with plants at top, lower* one sandy 

 and with very good plants 

 86.00 Gray and tan sandstones and conglomerates predominate 



Cupriferous horizons with plants at top. Casts of trunks 

 of trees in green up to 6 inches in diameter, in some 

 cases with pebbles within the casts 

 3.00 Gray conglomerate 

 60.00 Gray sandstones 

 1.50 Conglomerate 

 1 .80 Red sandstont 

 2.40 Red shale 

 i. 80 Red sandstone 

 3.00 Red shale 



7.50 Copper band with many stem casts, conglomeratic sandstone 

 75.00 Interbedded sandstones and shales 



