But this lower Uspallata Pass, which has always been the principal means of land communication with Argentina, was destined to become famous in another way, because (as already mentioned in the chapter on Argentina), it was the place chosen as the most suitable for the route of the Chilean-Argentine transcontinental railroad, connection between the eastern and western sections of which was established in April, 1910, by completion of a tunnel through the mountain two miles long and half a mile beneath the Cumbre—a work of the utmost importance, for, aside from the matter of comfort and saving of time, it has made it possible to go from one country to the other by the land route in winter, when the pass above is covered with drifts and the deadly winds and snowstorms are so likely to whirl down on the traveler at any moment that few except the hardy mail-carriers ever dared attempt it. In this neighborhood the mountains attain their greatest altitude. A few miles to the north and visible a little distance from the Cumbre is the “Monarch of the Andes,” Aconcagua, which, according to the record at the Harvard University Observatory in Arequipa (Peru), is 24,760 feet (more than four miles and a half) high—the highest in the world, it is now regarded, next to Mt. Everest in the Himalayas. In his interesting story of the ascent of Aconcagua, Sir Martin Conway, one of the very few who ever succeeded in accomplishing it, gives a good idea of the region, viewed from a point near the lesser of the two summits. “At last I heard a shout and looked up and saw Maquignaz a yard or two above my head,” he says,