52 STEPPES AND DESERTS. 



ral equatorial current of the waters of the ocean, and opposes a 

 barrier to the more rapid commercial intercourse of Europe and 

 Western Africa with the eastern parts of Asia. North of the 17th 

 degree of latitude and. the celebrated isthmus of Tehuantepec, the 

 mountains, quitting the coast of the Pacific, and following a more 

 direct northerly course, become an inland Cordillera. In North 

 Mexico, the " Crane Mountains" (Sierra de las Grullas) form part 

 of the Rocky Mountain chain. Here rise, to the west, the Colum- 

 bia and the Rio Colorado of California ; and, to the east, the Rio 

 Roxo de Natchitoches, the Candian, the Arkansas, and the Platte 

 or shallow river, a name which has latterly been ignorantly trans- 

 formed into that of a silver-promising river Plate. Between the 

 sources of these rivers (from N. lat. 37 20' to 40 13') rise three 

 lofty summits (formed of a granite containing much hornblende and 

 little mica), called Spanish Peak, James's or Pike's Peak, and Big 

 Horn or Long's Peak. (See my Essai Politique sur la Nouvelle 

 Espagne, 2me 6dit. t. i. pp. 82 and 109.) The elevation of these 

 peaks exceeds that of any of the summits of the Andes of North 

 Mexico, which, indeed, from the 18th and 19th parallels of latitude, 

 or from the group of Orizaba and Popocatepetl (respectively 2717 

 toises or 17,374 English feet, and 2771 toises or 17,720 English 

 feet), to Santa Fe" and Taos, never, reach the limits of perpetual 

 snow. James's Peak, in lat. 38 40', is supposed to be 1798 toises, 

 or 11,497 English feet; but of this elevation only 1335 toises (8537 

 English feet) has been measured trigonometrically, the remaining 

 463 toises, or 2960 English feet, being dependent, tin the absence 

 of barometrical observations, on uncertain estimations of the decli- 

 vity of streams. As a trigonometrical measurement can hardly ever 

 be undertaken from the level of the sea, measurements of inaccess- 

 ible heights must generally be partly trigonometrical, and partly 

 barometrical. Estimations of the fall of rivers, of their rapidity, 

 and of the length of their course, are so deceptive, that the plain 

 at the foot of the Rocky Mountains, nearest to the summits above 

 spoken of, was estimated, previous to the important expedition of 

 Capt. Fremont, sometimes at 8000, and sometimes at 3000 feet. 

 (Long's Expedition, vol. ii. pp. 36, 362, 382, App. p. xxxvii.) It 

 was from a similar deficiency of barometrical measurements that the 



