CHAPTER XXY. 
ECONOMICAL GEOLOGY. 
Localities of supply of building stone, and 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 supplies of stone and lime, 
which might be transported up the river 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 point, 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 canons 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. 
