the remaining 463 toises, or 2960 English feet, being dependent, in the absence of barometrical observations, on uncertain estimations of the declivity of streams. As a trigonometrical measurement can hardly ever be undertaken from the level of the sea, measurements of inaccessible 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. Frémont, 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 true elevation of the Himalaya continued so long uncertain: but now the resources which belong to the cultivation of science have increased in India to such a degree, that Captain Gerard, when on the Tarhigang, near the Sutlej, north of Shipke, at an elevation of 19411 English feet, after breaking three barometers, had still four equally correct ones remaining. (Critical Researches on Philology and Geography, 1824, p. 144.) Frémont, in the expedition which he made in the years 1842-1844 by order of the Government of the United States, found the highest summit of the whole chain of the Rocky Mountains to the north north-west of Spanish, James’s, Long’s, and Laramie Peaks. This snowy summit, of which he measured the elevation barometrically, belongs to the group of the Wind River mountains. It bears on the large map, edited by Colonel Abert, Chief of the Topographical Office at Washington, the name of Frémont’s Peak, and is situated in 43° 10′ lat. and 110° 13′ W. long. from Greenwich, almost 5-1/2° north of Spanish Peak. Its height, by direct measurement, is 12730 French, or 13568 English feet. This would make Frémont’s Peak 324 toises (or 2072 English feet) higher than the elevation assigned by Long to James’s Peak, which, according to its position, appears to be identical with Pike’s Peak in the map above referred to. The Wind River mountains form the divortia aquarum, or division between the waters flowing towards either ocean. Captain Frémont (in his Official Report of the Exploring Expedition to the Rocky Mountains in the year 1842, and to Oregon and North California in the years 1843-44, p. 70,) says, “We saw, on one side, countless mountain lakes, and the sources of the Rio Colorado which carries its waters through the gulf of California to the Pacific; and, on the other side, the deep valley of the Wind river, where are situated the sources of the Yellowstone river, one of the principal branches of the Missouri which unites with the Mississippi at St. Louis. To the north-west, rise, covered with perpetual snow, the summits called the Trois Tetons, where the true source of the Missouri itself is situated, not far from