Chap. XI. THE BUFA DE COSIHUIBTACHIC. 371 
follows the depression between them, called the Puerto de 
Coyachic (Pass of Coyachic). At first one does not see 
why, for the table-land around seems as level as the floor of 
a room. But nearer the two peaks, the plain is intersected 
by deep crevices, which are not visible till you are quite 
close to them. To the left of the twin mountains, a 
portion of the horizon intervening, rises another isolated 
mountain. This is the Bufa de Cosihuiriachic. Dr. Wisli- 
zenus w 7 as the first who marked the geographical position 
of this mountain peak ; but European geographers err in 
making it one of the main peaks and vertebrae of the Sierra 
Madre. The mountain rests upon the plateau, above 
which it is not much raised, at the edge of a deep ravine, 
from the bottom of which it may certainly have a con- 
siderable altitude. But above, it is entirely surrounded by 
the plain of the plateau and thus completely separated 
from the chain bearing the name of Sierra Madre, and 
from the axis of which it stands considerably to the east. 
It belongs in fact to the isolated groups occurring between 
the Sierra Madre and the town of Chihuahua. 
As regards this mountain chain and its celebrated name, 
I shall endeavour farther on, in a general survey of the 
orology of North America, to rectify the prevailing errors 
on this head. I will only now remark that in Mexico 
(including New Mexico and California) there are several 
mountains called Sierra Madre, not in the slightest degree 
connected, but which geographers have incorrectly placed 
in contact, and that the Sierra Madre mentioned at this 
part of my journey must be defined as a mountain girdle, 
consisting of thickly set parallel chains, which forms the 
western orolographical limit and edge of the Mexican 
table-land, but which, in a hydrographical sense, stands 
on the slope to the Pacific Ocean ; since the rivers passing 
2 b 2 
