As one proceeds from Mendoza the upper valley begins to close in and the track pierces the main range of the Cordilleras between walls of porphyry and granite. To the north one gets at last a glimpse of Aconcagua some twenty-three thousand and eighty feet above sea level, and higher than any peak outside of the Himalayas. It is more than ninety miles from the Pacific and can be seen on a clear day from Valparaiso, for its lofty head is lifted up above its neighbours. It is on the Argentine side, and all the melted ice and snow from its slopes pours down over the pampas of that country. It is surrounded by winding valleys, by rugged and precipitous spurs and ridges which are difficult of access. One of the best views is from the Puente del Inca where the Horcones Valley opens out into the Cuevas Valley. It has been termed a volcano, but there are no signs of a crater and few traces of scoriæ. To the north of Aconcagua lies the Mercaderio, over twenty-two thousand feet, and to the south Tupungato, just a few feet lower. On the Chilean side, near the Cumbre, is Juncal (19,500 feet), and near it are the peaks of Pollera, Navarro, Maipo and the great volcano of San José. The most striking aspect of these Andean solitudes is their terribly bleak and desolate appearance. Trees there are none, but only a few shrubs and blades of grass growing in the clefts of rocks here and there; nothing but a huge expanse of yellow sand and stone, with peaks rising on every hand whose extraordinary stratification presents many-coloured hues which are almost bewildering to the eye. Great torrents flow down their sides whose waters are of a dull, brackish colour. These are exceedingly rapid and full of dangerous holes, so that the fording of them is perilous. The line of perpetual snow is about seventeen thousand feet, although this varies. In the spring there is a very curious phenomenon at times on the glaciers and snow slopes. It consists of huge fields composed of cones, or pyramids, of frozen snow, some four or five feet high, placed close beside each other. These cones are called the _nieve penitente_, or penitent snow, because of its semblance to the cowled Penitent Friars. This effect is caused by the combined action of the sun and wind upon the frozen masses. Aconcagua is distant about a dozen miles from the Inca or Cuevas. The weather, however, is uncertain even in summer, and a terrible wind usually prevails after sunrise. These render exploration work difficult and even dangerous. In the winter the snowfall is excessive. In the summer there is no snowfall and the wind blows the dust from the desert-like valleys in stifling clouds, which are oftentimes almost unendurable. Storms which are almost blizzards spring up as by magic on the high altitudes. The lightning is especially vivid and dangerous.