110 COSMOS. 



highest portion we have just surveyed, and which from 

 south to north, from the tropical part to the parallels 

 of 42 and 44, so increases in extent from east to west 

 that the Great Basin, westward of the great Salt Lake of 

 the Mormons, has a diameter of upwards of 340 geogra- 

 phical miles, with a mean elevation of nearly 5800 feet, 

 differs very considerably from the rampart-like mountain- 

 chains by which it is surmounted. Our knowledge of this 

 configuration is one of the chief poinits of Fremont's great 

 hypsometrical investigations in the years 1842 and 1844. 

 This swelling of the soil belongs to a different epoch 

 from that late upheaval which we call mountain-chains 

 and systems of varied direction. At the point where, 

 about 32 lat., the mountain-mass of Chihuahua, accord- 

 ing to the present settlement of the boundaries, enters the 

 western territory of the United States (in the provinces 

 taken from Mexico), it begins to bear the not very definite 

 title of the Sierra Madre. A decided bifurcation, 16 however, 

 occurs in the neighbourhood of Albuquerque, and at this 

 bifurcation the western chain still maintains the general 



South America, Alcide D'Orbigny, Voy. dans I'Amerique merid. Atlas, 

 pi. viii. de Geologic spfoiale, fig. i. 



16 For this bifurcation and the correct denomination of the east 

 f.nd west chains see the large special map of the Territory of Neiv 

 Mexico, by Parke and Kern, 1851 : Edwin Johnson's Map of .Railroads, 

 1854; John Bartlett's Map of the Boundary Commission, 1854 : Ex- 

 plorations and Surveys from the Mississippi to the Pacific in 1853 

 and, 1854, vol. i, p. 15; and, above all, the admirable and comprehensive 

 work of Jules Marcou, Geologist of the Southern Pacific R. R. Survey, 

 under the command of Lieutenant Whipple, entitled Resume explicatif 

 dune Carte geologique des Etats Unis et d'un Profil geologique allant de 

 la vallee du Mississippi, aux cdtes del' Ocean Pacifique, pp. 113 116; 

 also in the Bulletin de la Societe geologique de la France, 2e Se"rie, t. xii, 

 p. 813. In the elongated valley closed by the Sierra Madre, or Rocky 

 Mountains, lat. 35 38i, the separate groups of which the western 

 chain of the Sierra Madre and the eastern chain of the Rocky Moun- 

 tains (Sierra de Sandia) consist bear different names. To the first chain 

 belong, reckoning from south to north, the Sierra de las Grullas, the 

 S. de los Mimbres (Wislizenus, pp. 22 and 54), Mount Taylor (lat. 35 

 15'), the S. de Jemez and the S. de San Juan ; in the eastern chain the 

 Moro Peaks, or Sierra de la Sangre de Cristo, are distinguished from 

 the Spanish Peaks (lat. 37 32') and the north westerly tending White 

 Mountains, which close the elongated valley of Taosand Santa Fe. Pro- 

 fessor Julius Frobel, whose examination of the volcanoes of Central 

 America I have already noticed (Cosmos, above, p. 274), has with rnuuh 



