CHAPTER XXV. 



ECONOMICAL GEOLOGY. 



Localities of supply of building stone, akd nature of material. 



Materials for building stone are plentiful, at small distances apart, on the route. On the 

 valley of the Rio Grande, above El Paso, the carboniferous limestone of the Organ mountains 

 crosses the river, and the proximity of the lofty hills afford abundant sujiplies of stone and lime, 

 which might be transported up the rirer for some miles. In the Mesilla valley the small hill 

 behind the town of Las Cruces is also of limestone, and is not more than three miles from the river. 

 Twelve miles west of the river buttes of trachyte and basaltic rocks occur, which can be quarried 

 extensively. The trachyte is a reddish hard rock, breaking with a sharp fracture, easily trim- 

 med, and wears well. The basalt is a hard, dark green rock, more difficult to work than the 

 trachytes. This overflow is from 20 to 25 miles across, and should the road pass to the south, 

 along the plain, the southern edge of this overflow will afford the place for quarries. 



Cook's Spring, 15 miles W. In this neighborhood porphyry andsyenitic rocks abound. The 

 latter are among the most durable of rocks ; both of these extend south of the spring for some 

 miles, and could, at that j)oint, furnish materials. Greenstone is also abundant there. The 

 Mimbres river, 21 miles W., on the immediate line of trail, does not afford building stone ; but 

 three miles up the river white and red sandstones and buttes of trachyte porphyry occur on the 

 left bank. The white grits are not coherent, at least in the upper layers. The reddish, yield, 

 in some of the beds, a very durable fine-grained stone, which will answer sufficiently well where 

 great pressure is not exerted. 



On the trail between the Mimbres and Ojo de'la Vacca these same sandstones crop out, but 

 do not rise above the road level ; they are favorably disposed, from their stratification, for 

 quarrying. 



The valleys and small caSons of the Burro foot hills, as at Penasquitas and other entrances, 

 are well supplied with porphyries, trachytes, and metamorphic quartz ; all hard rocks, and well 

 exposed, so as to be easily removed. Twenty miles west are the Pyramid hills, masses of por- 

 phyry and trachyte, with metamorphic sandstone ; and twelve miles further west lie the Pelon- 

 cillo hills, which are immense extravasations of volcanic rocks, porphyries, trachytes, and basalts ; 

 the first and the last are the rocks best adapted, from their durability and close grain. Fifteen 

 miles beyond the west edge of these hills the limestone of Chiricahui is reached, which, as it 

 encircles the whole mountain at its base, can be reached readily at the northern end of Chiri- 

 cahui, should it be desirable to turn the mountain. This rock is again met on the west side of 

 the playa, on the foot hills of Sierra Calitro. The granitic centre of this hill yields a good 

 stone. West of the San Pedro a similar granitic rock forms Santa Catarina, from which large 

 supplies will be required to be drawn. Two outcrops of granitic rock and sandstone occur 

 between the latter range and the Gila river, along the trail ; the sandstone is a friable rock, and 

 scarcely to be selected where the igneous rock can be had. 



