Fifth.—The pass of the Cumbre by Uspallata, the road most usually taken by travellers proceeding from Mendoza to Santiago de Chile, and which has been very particularly described by several Englishmen, who have gone that way. Of the published accounts that of Mr. Miers is, perhaps, the best, as he had the most opportunities of making it so, having crossed it no less than four times, once with his wife, who was taken in labour upon the road. Lieutenant Brand's is particularly interesting, from his having crossed at the season when the Cordillera was covered with snow, which obliged him to proceed on foot a great part of the way, and to encounter fearful risks, which he has very graphically described. The whole distance from Mendoza to Santiago is 107 post leagues; and the highest part of the Andes crossed is (by barometrical measurement), according to Dr. Gillies, 12,530 feet above the sea:—Mr. Miers says about 600 feet less. From the commencement of November to the end of May, occasionally a few weeks sooner or later, this road is passable the whole distance on mules:—for the rest of the year it is generally closed to all but foot-passengers, and the crossing is then attended with considerable danger; many lives have been lost in attempting it.
A striking object on this road is the splendid arch called the Inca's Bridge, seventy-five feet over, which nature has thrown across a ravine one hundred and fifty feet deep, through which runs the river of Las Cuevas. There are natural hot springs about it, which some persons suppose to have contributed to its formation:—it is evident, however, that some infinitely more powerful agency has been at work, from the appearance of beds of fossil shells there at an elevation of 8650 feet above the level of the present sea.
Sixth.—About half way over, near the station called the Punta de las Vacas, a road branches off to the valley of Tupungato, and afterwards crosses the Cordillera to the north of the peak so called, descending on the opposite side into Chile by the valley of the little river Dehesa, from which it is called the Dehesa Pass: it is very little used.
Seventh.—South of the mountain of Tupungato is the Portillo Pass, which falls into the valley of the river Maypú in Chile with the Rio del Yeso. By many travellers it is preferred to the high road by Uspallata, being the shorter way of the two by twenty leagues:—it is, however, seldom open longer than from the beginning of January to the end of April, the greater elevation of that part of the Cordillera causing it to be longer blocked up by the snow.
The way to it from Mendoza runs southward, parallel to the mountains as far as the estancia of Totoral, upon the north bank of the river Tunuyan, distant about sixty-five miles from that city, and some twenty from the base of the Cordillera:—thence the pass bears west-south-west, distant about thirty-six miles; the breach in the mountains through which the Tunuyan runs being plainly visible to the south of it. This part of the Andes seems to consist of two great parallel ridges running nearly north and south, and separated from each other by the valley of the Tunuyan, the width of which is about twenty miles, and its elevation above the sea, where crossed by the road, about 7500 feet. Of the two ranges the eastern one is the highest, being, where the road crosses it, 14,365 feet above the sea:—this chain extends with little interruption from the river of Mendoza, southwards, to the Diamante, a distance of about 140 miles:—the western, or Chilian range, where crossed by the road, is not above 13,200 feet high.[76]
In this part of the Cordillera is situated the volcano of Peuquenes, or Maypú, eruptions from which have been frequent since the great earthquake which produced such disturbance in 1822:—they generally consist of ashes and clouds of pumice-dust, which are carried by the winds occasionally as far as Mendoza, a distance little short of 100 miles. In crossing from the eastern to the western side of the valley of the Tunuyan travellers have, at first, the summit of the volcano concealed from them, but about half way between that river and the pass of Peuquenes there is a good view of it eight or nine miles distant to the south:—the summit is generally covered with snow, and cannot be much less than 15,000 feet above the sea. It is from the pumice-rock found in this neighbourhood that the people of Mendoza make basins for filtering the muddy water of their river.
Eighth.—To the south of this volcano is situated a pass called De la Cruz de Piedra, which enters the Cordillera where a small stream, the Aguanda, issues from it, about two leagues to the north of the fort of San Juan:—it unites with the road by the Portillo pass on the opposite side of the Andes in the valley of the Maypú.
Ninth.—Further south one little frequented unites the valleys of the rivers Diamante and Cachapoal: this is previous to reaching the volcano of Peteroa, beyond which are situated the passes of Las Damas and of the Planchon.
Tenth.—Of these the Las Damas, or ladies' pass, enters the Cordillera from Manantial in the valley of the river Atuel, and descends by that of the Tinguiririca, which issues from the mountain of San Fernando:—this was the pass which M. de Souillac, in 1805, reported might, at a very small expense, be rendered passable for wheel-carriages.[77]