the last report of the Secretary of War. It will enable the reader to understand the details which follow, as to the various passes of the mountains suggested by different enterprises. "The western portion of the continent of North America, irrespective of the mountains, is traversed, from north to south, by a broad, elevated swell or plateau of land, which occupies the greater portion of the whole space between the Mississippi river and the Pacific Ocean. The crest of this plateau, or the water-shed of the country, is nearly midway between the Pacific coast and the Mississippi. It may be represented on the map by an undulating line traced between the head waters of the streams which flow eastward and those which flow westward. It divides the whole area between the Mississippi and the Pacific into two nearly equal portions—that on the east being somewhat the larger. This crest of the water-shed has its greatest elevation in Mexico; and thence declines to its lowest point about the latitude of 32°, where it has a height of about four thousand five hundred feet, between the waters of the Rio Grande and those of the San Pedro, a tributary of the Gila: From this parallel it increases in altitude northward, and reaches its maximum near the 38th parallel, where it is about eight thousand feet high. Thence it declines as we pass northward; and, in lat. 42° 24', it has an elevation of say seven thousand feet; and, in the latitude of about 47°, it is reported to be at least one thousand feet lower. The heights here given are those of the lowest passes over the

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crest or water-shed of the great plateau of the country, and not those of the mountain peaks and ridges which have their base upon it, and rise, in some cases, to the height of seventeen thousand feet into the region of perpetual snow.

"The slope of the plateau, on the east and south, towards the Mississippi and the Gulf of Mexico, is comparatively gentle; and, in Texas, is by several steps, of which the highest is that known by the name of Llano Estacado, or Staked Plain. It is traversed by the Missouri, the Platte, the Arkansas, and other large rivers which rise among the mountains near the crest, and flow eastward and southward in channels sunk beneath the general surfacelevel of the plains.

“In lat. 42°, near the source of the Platte, it has an elevation of about five thousand feet above tide, and in the same latitude on the Mississippi about one thousand feet. Towards the sources of the Arkansas, in lat. 36°, it has a height of four thousand feet; and in the same latitude on the Mississippi, two hundred and seventy-five feet. These elevations give an average declination, eastward, to the whole plain, of about four and a half feet per mile, and southward, of about two and a third feet.

"The crest of the plateau, and nearly the whole of its western portion to the Pacific, is occupied by a great mountain system-the continuation of the Andes of South America. It has a variable breadth, narrowest within our possessions, near the Gila, in lat. 32°, where it has a width

of about five hundred miles, and attains its greatest expansion in the parallel of 40°, where it occupies a space of about nine hundred miles. On this mountain base, as has been said before, are situated a series of elevated peaks, ridges, and ranges. Those on the eastern side are nearly continuous for about nine hundred miles, and known by the name of the Rocky Mountains; those on the western side are perhaps less continuous, though equally elevated above their base, and designated as the Sierra Nevada, Coast Range, Cascade Mountains, etc. The whole space between these extreme ranges is occupied by high peaks, and in various directions by a series of ridges, including elevated valleys, and forming great basins, having no outlet to the sea. The most important of these is Salt Lake Basin, having an elevation of four thousand one hundred feet.

"This mountain region is not, as is frequently supposed, a single chain, but a system extending from a little east of the crest of the water-shed to near the shores of the Pacific, and occupying about one-half of all the space between the Mississippi and the Pacific Ocean. The position of this belt of mountain region, stretching from north to south, gives rise to a peculiarity of climate and soil. Fertility depends principally upon the degree of temperature and amount of moisture, both of which are much affected by increase of elevation; and the latter, also, depends on the direction of the wind. The upper or return current of the trade-wind, flowing backward towards the north-east, gives a prevalence

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of westerly winds in the north temperate zone, which tends to spread the moisture of the Pacific over the western portion of our continent.

"These winds, however, ascending the western slope of the mountain ridges, are deprived of their moisture by the diminished temperature of the increased elevation; and hence it is that the plains and valleys on the eastern side of the ridges are generally parched and barren, and that the mountain system, the highest chain of which, known as the Rocky Mountains, by presenting, as it were, a screen against the moisture with which the winds from the west come laden, has for its eastern margin a sterile belt, which probably extends along the whole range, with an average width of about two hundred and fifty miles."

There is no physical difficulty of more than ordinary character in the way of a railroad route from the Mississippi to the eastern base of the great mountain region thus described, or to what is usually called the line of the Rocky Mountains. The slopes are gentle, and an average ascent of about six feet to a mile would carry a railroad route to the great sandy plains which stretch about two hundred or three hundred miles east of the mountains proper. The route through the plains, and then through the ridges of the mountains themselves, becomes the question of especial practical interest. The various passes proposed refer to different methods of crossing this region. To describe these several passes through the mountains, in the order in which

they have claimed public attention, we speak first of the South Pass. This is at the head of the Sweet Water river, one of the highest tributaries of the North Fork of the Nebraska. It was early known to the trappers, and is described in Capt. Bonneville's adventures, as Mr. Irving has presented them. It was first examined with scientific precision by Lieut. Fremont, in 1842, and afterwards, on his return from the Pacific, in 1844. In his journal of that year he gives the following account of this remarkable highway between the oceans:

"The morning of August 13th was clear and cold, there being a white frost, and the thermometer, a little before sunrise, standing at 26.5°. Leaving this encampment (our last on the waters which flow towards the rising sun), we took our way along the upland, towards the dividing ridge which separates the Atlantic from the Pacific waters, and crossed it by a road some miles further south than the one we had followed on our return in 1842. We crossed very near the Table Mountain, at the southern extremity of the South Pass, which is near twenty miles in width, and already traversed by several different roads. Selecting as well as I could, in the scarcely distinguishable ascent, what might be considered the dividing ridge in this remarkable depression in the mountain, I took a barometrical observation, which gave seven thousand four hundred and ninety feet for the elevation above the Gulf of Mexico. You will remember that, in my report of 1842, I estimated the ele