Eleventh.--The road by the Planchon leads to Curico and Talca, following the courses of the rivers Claro and Teno:--on neither of these roads does the elevation exceed 11,000 feet, or the vegetation ever cease. The twelfth pass is that of Antuco, from which Cruz started in 1806 to cross the Pampas to Buenos Ayres:--the road by it to Conception in Chile follows the valleys of the rivers Laxa and Biobio. To the south of the volcano in the vicinity of this pass, which Cruz could not get up, but which has since been ascended by M. Pæppig, a German naturalist (who nearly lost his life in the attempt), lies a ridge called the _Silla Velluda_, rising, according to his estimation, to the height of 17,000 feet, on the rugged sides of which, below the snow and glaciers, are to be traced ranges of basaltic columns. Of the most frequented of these passes, viz., those by Uspallata and the Portillo, there are, as I have already said, several accounts in print, but, as I know of no other Englishman except the late Dr. Gillies who has examined those of Las Damas and the Planchon with any attention, I shall here quote part of a letter which he wrote to me in 1827, giving an account of a short excursion he made by them in that year; and I do so the rather because it also gives some account of the intervening country, which has never, as far as I know, been described by any one else:-- "About the middle of May I returned from an excursion of ten weeks to the south which I had long meditated. After reaching the river Diamante, the southern boundary of the province of Mendoza, I crossed that river and ascended the Cerro del Diamante, and at every step found ample evidence of its volcanic origin: the ascent was covered with masses of lava, and near the summit with loose pumice. The upper part of the mountain consists of a ridge elevated a little at each of the extremities into a rounded form, on the north side of which, a little below the summit, is a plateau about 400 yards in diameter, which undoubtedly has been formerly the crater of a volcano. The whole mountain appears to rest on an immense bed of pumice-stone. On the steep banks of the Diamante opposite to it such strata are laid open on both sides:--at one place on the south bank I traced one great mass of pumice-rock, 100 feet long and 145 wide, the whole forming distinct basaltic pillars.