Chap. VIII. SIERRA MADRE OF CINALOA AXD SONORA. 557 
than it is in reality, and the hypothesis of a connexion has 
gained in probability and confirmed the error. 
VI. — The last north-western spurs of the Sierra-Madre 
system are crossed by Cook's Eoad, south of the river 
Gila, in the tract between the Guadalupe Pass and Fort 
Yuma. Near this fort, and consequently near the con- 
fluence of the Gila and Colorado, the chain of mountains 
which extends along the coast of Sonora and Cinaloa, and 
forms the western foot of the Sierra Madre system, a sys- 
tem consisting throughout of parallel chains, has its north- 
western termination : but on the other side of the Gila and 
Colorado it is continued by a mountain range, which the 
traveller has on his right at some distance on his road 
through the desert. In a pointed angle it advances 
toward the chain extending from the peninsula of Cali- 
fornia, until they unite. Persons who have visited this 
part of the country inform me, that the peak of San 
Bernardino is the central point of their junction. The 
extreme north-western continuation of the Sierra Madre 
system thus unites with the mountain range which C ali- 
form an geologists call the San Bernardino range, but 
which was known to the old Mexican Californians. as I 
have before said, under the same name of the Sierra 
Madre. If therefore the Sierra Madre of Cinaloa and 
Sonora has a northern equivalent, we must look for it not 
in the Rocky Mountains, but in the Califomian system. 
The real character of the orographic structure of this 
region, however, only becomes clear when we consider it 
as belonging to the general configuration of the western 
half of the continent. 
VII. — The centre of this western half, following the 
direction of the coast of the Pacific, from the isthmus of 
Tehuantepec to the Arctic Ocean, is occupied throughout 
