THE SMITHSONIAN INSTITUTION. 275 



expressly under a geological point of view, would say that these 

 mountains respectively belong to each other. Even not to augment 

 the sufferings of schoolmasters and schoolboys, v.-e should abstain from 

 innovations which would oblige them to become good geologists before 

 they could understand, the one what he is teaching, the other what he 

 is learning. The outward forms of the surface of our globe should 

 be considered independently of the system of geological periods and 

 mineral masses. The knowledge of each, though there is an inlimate 

 connexion between the two, has its own peculiar interest, and the 

 claims of the geologist in that respect have no better foundation than 

 those of the botanist who would propose to give different names to 

 two sections of the same chain of mountains, because one is covered 

 with pine trees, the other with oak. 



After these preliminary remarks, intended to clear the subject of 

 some confused notions in respect to its general principles, I ma}^ pass 

 over to a statement of facts, which shall be mostly such as have fallen 

 under my own observation. 



1. The great chain of the Rocky Mountains divides, in the neighbor- 

 hood of the origin of the Rio Grande, into two ranges, of which one 

 runs along the eastern, the other along the western side of that river, 

 down to about the latitude of Santa Fe. 



Every one who has travelled from the Missouri river to the capital 

 of New Mexico, is well aware of the fact that the latter part of the road, 

 from Las Vegas to its termination, turns round the southern promontory 

 of the eastern range. To the north he leaves steep, high, and mostly 

 snow-covered mountains, while the elevations to the south are of two 

 kinds, but both different in character from the great chain to the north. 

 Some there are, it is true, which have been caused by plutonic eruptions, 

 and the upheaval of metamorphic and sedimentary masses ; but they 

 are merely little isolated groups, or ridges, such as the Placer, Sandilla, 

 and Manzana mountains. The rest are either mere declivities, or de- 

 tached portions of the general table land. This latter, at an average 

 altitude of nearly 7,000 feet above the sea, turns round that same south- 

 ern promontory, from the eastern to the southwestern side of the great 

 chain, and, running out here in a projecting corner to the westward, 

 reaches the very borders of the valley of the Rio Grande, where, at 

 many places, the traveller has a view over its edges down into the val- 

 ley near Albuquerque. The little groups and ridges just mentioned 

 have entirely the general character of the numerous mountains which, 

 like the islands of an archipelago, are scattered all over the high plains 

 of western Texas and Mexico. If, nevertheless, they be considered 

 as the southern continuations, or representatives, of the Rocky Moun- 

 tains, which in a certain sense they really are, it should be in view 

 of the correspondence of the natural arrangement of elevations in that 

 section of country to the western terminal range, which, south of Santa 

 Fe, appears to pass over to the eastern side of the river, following, 

 in this way, the general south-by-east course of the system. 



2. Whoever has travelled from EI Paso to California by the Gila 

 route knows that, following Cook's route in its southern bend, he has to 

 pass over several mountain spurs ; but that, choosing the straight line of 

 a more northern track, called Leroux's route, he passes from the Rio 



