154 VOLCANIC ROCKS OF THE DISTURBED DISTRICT. 



■without dislocating the strata so much as to tilt them up sharply. They have been dislocated 

 very much in places, but the result has apparently been to produce faults, as if the whole strata 

 had been elevated, and afterward, settling down unequally, produced the fissures or faults. It 

 is worthy of remark that each valley, from the Santa Catarina range, with one exception, is at 

 a higher level the more east it lies, thus : 



Elevation of the San Pedro at Tres Alamos-. 3,413 feet. 



Elevation of Valle de los Pimas 4,127 " 



Elevation of Valle del Sauz 3,815 " 



Elevation of Valle de los Playos, west side 4, 269 " 



Elevation of Valle de los Playos, east side 4,330 " 



Thus, the effect of the Peloncillo range is to elevate the valley east of it over 450 feet, and 

 the smaller range of the Pyramids appears to lift its valley 60 feet above its neighbor. 



The trachyte and basalt country here blend together, forming a very elevated rugged land of 

 hill and small valley, with rough caiions ; it abounds in small wells and springs, which are found 

 in the canons, from four to six miles ajiart, the water being clear and wholesome. 



BUERO MOUNTAINS, PENASQUITAS. 



Leaving this valley of the Playas to the east, the foot hills of the Burro mountains are entered. 

 These, in constitution, resemble the Peloncillo and the Pyramid hills, and differ from Chiricahui 

 in this regard, that they have not a central igneous nucleus around which the strata are inclined, 

 but are rather a series of waves, upraising great breadths of land, with bluffs generally to the 

 east, and sloping more gradually westward ; and though these hills individually attain no great 

 elevation, the whole country appears to have been lifted up considerably. These porphyritic 

 chains appears to have a pretty uniform direction N. 60° W., which is a much greater inclina- 

 tion than either Chiricahui on one side, or the Organ mountains, on the Rio Bravo, on the other. 

 By this trend of the hill ranges open low canons running east and west traverse them every- 

 where, and passes from one valley to another are easily found. The yellow sandstone is in 

 some places hardened like enamel ; in others, converted into agatized layers. The Burro hills, 

 whose southern extension is crossed at Penasquitas, and forms the rolling country at Ojo de la 

 Inez and Ojo de la Vacca, lie more to the north, where they are gathered round the banks of 

 the Gila, through which the river canons. They are there lofty rugged masses of sandstone, 

 broken through by trachyte and porphyries, narrowing the bed of the river, and diverting it 

 northerly from its previous southern course. As the chain passes south, it drops down at the 

 point where the trail crosses. None of the hills exceed 700 or 800 feet in height. 



Exposures of rock in the caiion leading to the Ojo de la Inez showed the same succession of 

 trachyte and porphyry rocks as on the Peloncillo ridge. The valley of the caiion ran up north- 

 west, and was about 250 yards wide near the spring or water-pool. On each side the hills rose 

 from 250 to 300 feet, capped at the summit by trachyte, covering up yellow sandstones and 

 conglomerates. Thus, one hill, on the south side of the valley, viewed from above, downwards, 

 afforded the following structure : , 



The estimation in feet is approximate. 



Trachyte porphyry 30 feet. 



Metamorphic sandstone 25 " 



Blue silicious and chalcedonlc rock ._ - 20 " 



Talcose and trachyte layer 2 " 



Yellow sandstone shale, dip 12° N. 20° W 45 " 



Conglomerate of agatized pebbles - - - 60 " 



172 " 



