Our knowledge of the systems of mountains which, north of the parallels of 30° and 31° N. lat., are called the Rocky Mountains and the Sierra Nevada of California, has received most important additions, geologically, botanically, hypsometrically, and geographically by astronomical determinations of position, from the excellent works of Charles Frémont (Geographical Memoir upon Upper California, an illustration of his Map of Oregon and California, 1848); of Dr. Wislizenus (Memoir of a Tour to Northern Mexico, connected with Col. Doniphan’s Expedition, 1848); and of Lieutenants Abert and Peck (Expedition on the Upper Arkansas, 1845; and Examination of New Mexico in 1846 and 1847.) There prevails throughout these different North American works a true scientific spirit, which is deserving of the greatest commendation. The remarkable elevated plain, which rises to an uninterrupted height of four or five thousand French (4260 and 5330 English) feet, between the Rocky Mountains and the Sierra Nevada of California, of which I have spoken in p. 44, and which is called the Great Basin, forms an inland closed river basin, and has hot springs and salt lakes. None of its rivers,--Bear River, Carson River, and Humboldt River,--find their way to the sea. The Lake, which I was led by combinations and inferences to represent, in the great Map of Mexico drawn by me in 1804, under the name of Lake Timpanogos, is the great Salt Lake of Frémont’s Map: it is sixty geographical miles long from north to south, and ten broad; and it communicates with the fresh water lake of Utah, which is situated at a higher level, and receives the Timpanogos or Timpanaozu River, which enters it from the eastward, in lat. 40° 13′. The circumstance of the Timpanogos Lake of my map not having been placed by me sufficiently far to the north and west, is to be attributed to the entire want, at that time, of any astronomical determinations of the position of Santa Fé, in New Mexico. The error amounts, for the western margin of the lake, to almost 50 minutes of arc; a difference of absolute longitude which will appear less surprising, if it is remembered that my itinerary map of Guanaxuato could only be based for 15 degrees of latitude on compass surveys, or compass directions, for which I was indebted to Don Pedro de Rivera. (Humboldt, Essai polit. sur la Nouvelle Espagne, T. i. pp. 127-136.) These directions being differently combined by my early deceased fellow-labourer, Herr Friesen, and myself, gave him as the result of his combinations 107° 58′ from Paris as the longitude of Santa Fé, and to me as the result of mine, 107° 13′. According to actual astronomical determinations since obtained, the true longitude appears to be 108° 22′ W. of Paris, or 106° 00′ W. of Greenwich. The relative position of the beds of fossil salt--found in “thick strata of red clay,” on the south east of the island-studded Great Salt Lake (my Laguna de