50 
RIO GRANDE COAL FIELDS OF TEXAS. 
[BULL. 164. 
angle, and soon plunges beneath the overlying sandstones and clays to a 
depth too great for profitable working. Concerning the extent of this 
field in the Santa Rosa district of Mexico, Hill says: 1 
This coal field (the Santa Rosa) is the foundation of the whole valley or plain, and, 
except where covered by remnants of the later volcanic and conglomerate terrace, 
it is everywhere exposed. Next to the Sierra Chiquita, or Hog Backs, the coal is 
IOLD COALMINE TUNNEL 
(hartz mine) 
Fig. 9. — Sketch map showing coal mines and prospects near Eagle Pass; furnished by Louis Dolch. 
turned up in vertical stratification and is worked within a quarter of a mile of the 
entries of several mines. The coal beds extend from the foot of the Santa Rosas north- 
ward over the entire valley of the Sabinas, and at San Felipe, some 28 miles northeast 
of the concession, the coals are extensively mined and the product shipped to Texas, 
New Mexico, and Mexico in enormous quantities. These coals are not to be compared 
with the imperfect fibrous lignites of eastern Texas or the impure Carboniferous coals 
of that State, but they are the true Rocky Mountain Cretaceous coals, of anthracite 
luster, and by far the best fuel in America except the true anthracites of Pennsyl- 
vania, ranking higher than the bituminous of the Appalachian region. 
Report to the Ministro de Fomento upon the geology of the Santa Rosa mining district. 
