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Show 220 HYPSOME1'RIC ADDENDA. 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-laborer, Herr Friesen, and myself, gave him as the result of his combinations 107° 58' from Paris, as the longitude of Santa Fe, 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 Timpanogos), and not far from the present Fort Mormon and the Utah Lake-was given with perfect correctness in my large map of Mexico. I may refer on this point to the latest evidence of the traveller who made the first well-assured determinations of geographical position in that district: "The mineral or rock salt, of which a specimen is placed in Congress Library, was found in the place marked by Humboldt in his map of New Spain (northern half), as deri'Ved from the journal of the missionary Father Escalante, who attempted (1777) to penetrate the unknown country from Santa Fe of New Mexico to Monterey of the Pacific Ocean. South-east of the Lake Timpanogos is the chain of the Wha-satch Mountains ; and in this, at the place where Humboldt has written Montagnes de sel gemme, this mineral is found." (Fremont, Geogr. Mem. of Upper California, 1848, pp. 8 and 67; compare Humboldt, Essai politique, t. ii. p. 261.) A great historical interest attaches to this part of the highland, and more particularly to the country round the Lake of Timpanogos, which is perhaps the same with the Lake of Teguayo, the ancestral seat of the Aztecs. In their migration from Aztlan to Tula, and to the Valley of Tenochtitlan (Mexico), this people made three haltingplaces or stations, at which the ruins of the Casas grandes are still to be seen. The first sojourn of the Aztecs was at the Lake of |