Avalanches and snowslides were another constant menace. Their accustomed paths had to be noted carefully and then studiously given a wide berth. These convulsions are of impressive severity in the Andes, and the impetus the slides gain, owing to the steepness and length of the declivities down which they tumble, imparts terrific force to them. When a slender railway stands in their path it is caught up like straw and scattered in all directions. Possibly the landslides are more to be dreaded than the movements of the snow. In the Andes the denuding forces of Nature are exceptionally heavy. Many a mountain slope which, from a cursory inspection, looks substantial and solid, upon closer investigation proves to be merely a thick layer, perhaps many feet in thickness, of soft detritus. The slightest vibration is sufficient to set the mass in motion, and it slides slowly and irresistibly downwards. At some places it was found impossible to avoid such unstable ground, so the engineers ingeniously cut a passage through the soft rubble, taking care to reach the solid mountain flank beneath upon which to build the track, while the detritus was held back by means of massive concrete masonry walls.
Under such circumstances it is imperative that the track should be of the most solid character, if it is designed to fulfil the conditions of a trunk highway. The road bed is well built, laid with metals to a metre-gauge, and ballasted heavily. All earthworks are carried out on liberal lines, and the bridges are built throughout of steel.
When the main range is gained the line becomes more devious, the banks are sharper and more numerous, the short tunnels and the bridges across the rivers more frequent, for the location caused the line to swing from bank to bank as being more economical construction than to blast and carve a way for the line through the solid rock of the cliffs. At places the rises became so abrupt as to defy operation by adhesion. Then short lengths of rack where cog-wheels on the locomotive mesh with a toothed rail laid between the ordinary rails, and working similar to a rack and pinion, had to be inserted to enable the train to climb upwards.
A striking evidence of the distance saved by the railway is afforded between Mendoza and Upsallata station. As the crow flies the distance is 40 miles due east; by rail it is 17 miles farther; but by the old mountain road which converges upon the line at Upsallata it is no less than 100 miles! The latter makes a wide, sweeping detour after leaving Mendoza in order to avoid the foot-hills, and to ensure an easy gradient for animal traffic. The wildest part of the range is encountered when the Mendoza River is left and the railway enters the Amarillo, or Yellow Gorge. Incidentally, the line through this rift was one of the most costly and difficult sections to build. Las Cuevas, at an altitude of 10,388 feet, was the objective, and so great is the difference in level within a few miles that some daring development work had to be carried out. The first sign of this steep climb is a Meiggs V-switch. The rack was adopted more extensively, this being introduced between short stretches of easier grade or sections of level, so that the railway really ascends in the form of a series of gigantic steps. The rack is of the three-toothed type similar to that so familiar on the Swiss mountain railways.
In winding through the gorge some of the most impressive vistas of Andine majesty are unfolded. There is the snow-capped crest of Aconcagua, beetling 23,500 feet to the sky, Tupungato 21,451 feet, Tolosa 19,000 feet, and many another white-hooded mountain giant. The Trans-andine ranks as one of the greatest scenic railways in the world, for it unlocked the door to what previously was regarded as one of the most inaccessible sight-seeing centres on this globe. Already its station at Inca has developed into a popular mountaineering rendezvous, whence the ambitious essay to scale the caps of the Cordilleras. Some idea of the stupendous character of the railway’s ascent in this region may be gathered from the fact that in the last 8 miles to Las Cuevas it rises no less than 1,414 feet, and at this latter station the track lies nearly 2 miles above the Atlantic.
Las Cuevas is at the foot of the summit ridge which is pierced by the tunnel carrying the railway into Chile. This part of the work proved the most trying, for it involved wrestling with innumerable difficulties of great magnitude and peculiar character, such as are experienced very seldom in tunnelling operations. Though the range is not pierced at such an altitude as by the famous Galera tunnel in the country next door, yet it is three times as long.
The engineers had to drill, blast and excavate their way through the rock of the ridge for 10,000 feet—nearly two miles—and at times the obstacles that loomed up suddenly proved extremely perplexing. The completion of this work delayed the opening of the railway considerably, for calculations and anticipations were upset rudely when excavation commenced.
Some time passed before the precise design of the tunnel could be settled. At first it was decided to describe a spiral in the peak so as to accommodate the level of the Argentine division with that of the Chile section of the line. The tunnel was to be driven from either end by the engineers of the respective railways, which were two distinct undertakings. The two armies were to meet at mid-tunnel immediately beneath the famous statue of Christo Redentor, commemorating the treaty of peace between Argentina and Chile, which stands upon the boundary line of the two countries in the pass above.
On the Argentine side the camps for the tunnel works were established at Las Cuevas, about 1½ miles below the portal. When boring was commenced the engineers’ advance was threatened. The depth of the loose, friable earth eroded from the peaks above, which had accumulated during the flight of centuries, proved much greater than was supposed. This entailed most elaborate timbering to prevent the roof caving in and burying the excavators. As all lumber had to be brought up from Mendoza, for this desolate region is far above the timber line, heavy delays arose pending the arrival of the wood. Then they had to move forward warily foot by foot, as the detritus proved treacherous to handle. The engineers ploughed their way through this material for 300 feet, and felt relieved when at last they struck solid rock, which they rightly thought was the main body of the mountain. Elaborate arrangements were made to drive ahead more rapidly, but when the mass had been penetrated for nearly 200 feet the engineers received another rude shock. The rock was false. What they had fondly thought to be the mountain itself was merely a huge crag which had become detached and had slipped down bodily.
Here was a critical dilemma. The work was far too risky for aught but expert tunnel-builders—engineers who had made a speciality of such undertakings, and who were possessed of competent ability and facilities to cope successfully with any contingency likely to develop. As a result of careful deliberations it was decided to hand the whole tunnel—lock, stock and barrel, from end to end—to one firm. Selection fell upon the British engineers, Messrs. C. H. Walker & Company, who rescued the famous Severn tunnel from flood, and successfully completed it in the face of unheard-of difficulties.