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]