372 OKOLOGICAL REMARKS. Book II. 
through this region to the Gulf of California rise on the 
eastern side of the chain, on the table-land itself, and 
only reach the western side by forcing their passage 
through this mountain girdle. This definition agrees strictly 
with the terms used in the country, according to which the 
name of Sierra Madre is never extended to the chains and 
groups of a table-land. Indeed, these can in no respect 
be looked upon as spurs from that mountain barrier. 
On the contrary they mostly run parallel to it, rising from 
the plateau, like islands of an extensive Archipelago rise 
from the sea. 
According to Wislizenus, the Bufa de Cosihuiriachic 
has an elevation of 7918 feet above the level of the sea, 
and 1643 above that of the little town of Cosihuiriachic. 
As this is situated in a cleft of the table-land surrounding 
the mountain, at the depth of at least 700 feet, the 
summit of the mountain must be about 900 feet above the 
plateau, and the latter about 7000 feet above the sea. From 
hence, north-west to Cerro Prieto, the small lake of which 
lies on the broad watershed between the Mexican and 
Californian Gulfs, the level gradually rises. At Carre tas, 
on the contrary, it is lower, and at Santa Ysabel still 
lower. The plain of Chihuahua, as already mentioned, is 
only about 4600 feet above the sea level, and the Eio 
Grande, in a neighbouring portion of its course, has a 
fall, calculated at from 3000 to 4000 feet. Thus it fol- 
lows that, from the Kio Grande to the eastern base of the 
Sierra Madre, the general level of the table-land rises 
gradually for about 3000 or 4000 feet. 
To return to our journey. The road upon the slowly 
ascending plateau was so good that our horses took the 
eighteen miles to the foot of the pass of Coyachic in aconstant 
trot. The lofty plain exhibited very remarkable scenery. 
