i;3H Th< Ann rtfil II (trohn/isf. St-pteinbfr, IHiJl 
liasiii inountaiiis <»c-i-iinintz: in isolated blocks, a tyi)(' of wliiclMvill 
now l)e described in llu' Santa Rosa mountains. 
These mountains lie south of the Rio Sabinas and west of the 
Mexican International railway, and rise about H.OOO feet above 
the phiin. They are composed entirelj* of blue Cretaceous lime- 
stone of the Conuinche series, here metamorphosed into the firm 
aspect of the Silurian limestones. 
The Sierra de Santa Rosa are among the first true mountains, 
/. r. mountains produced by dislocated or folded stratification, 
met in northern Mexico. They are the eastern flank of the out- 
liers of the great l)asin group or system which extends'southwest- 
ward through the Trans-Pecos region of New 3Iexico and Texas 
into northern ^lexico, and are the V>eginning of the great mineral 
district of the latter region. These mountains rise in beautiful 
profile al)Ove the plain which surrounds them and extends north 
of them to the Rio Grande, and at a glance they nuirk the be- 
ginning of an entirely distinct geographic and geologic region 
from the Atlantic coastal region. 
Northeastward of these mountains towards Laredo* and p]agle 
Pass extends the plain or basin, which 1 have described as the 
Rio Grande eml)ayment which, carved V)v erosion into valleys and 
small hills, is a unique geographic feature constituting the drain- 
age basins of the Rio Sabinas and Rio Grande and sometimes 
called the San Felipe Coal Basin. 
1. Thr MoinUdlits. The Sierra Santa Rosa is an interesting 
piece of mountain architecture, consisting of an elongated mass 
or block of hard rock structure surrounded on every side by level 
plains. They extend northwest for fift}- miles west of Baroterau. 
The mountain is about ten miles wide upon an average, and the main 
axis or ridge is unbroken by passes. Geographically this moun- 
tain always presents three persi.stent and interesting longitudinal 
divisions, (a) The Sierra Grande or main mountain constituting 
the main central axial mass or backbone of the range standing 
about 1,500 feet above the plain of the basin, (b) The Sierra 
Chiquita or hog backs — a row of sharp angular mountains, which 
lie parallel to and on the north side of the Sierra'^p roper. There 
are some fifteen of these separated from each other by narrow can- 
ons of erosion, and from the Sierra Grande by^an irregular grand 
cliasm. These Chiquitas are about oOO feet above the plain, and 
are the most imj)ortant of the geographic divisions, economically, 
