December 15, 1910] 



NATURE 



2 19 



THE TRANSAXDINE RAILWAY. 



T T was on March 29, 1835, that Charles Darwin, who 

 -*■ had reached Mendoza from \"alparaiso by Peuquenes 

 and Portillo, set out on his return journey across the 

 Andes by the more northern line of the Uspallata and 



Fig. I. — Valley of the Rio Mendoza below Piiente eel Inca, looking up stream; the rack rail is 



s.en in the forearcur.d.* 



Cumbre passes, which has always been the principal 

 means of communication between the pampas and the 

 Pacific Coast. It was not until twelve days later that he 

 reached Santiago, though no doubt a less ardent geologist 

 might have completed the journey in 

 somewhat shorter time. It could now 

 be easily accomplished by rail in less 

 than the same number of hours. 



The Transandine railway is constructed 

 on the metre gauge, like many of the 

 Indian lines, although it links up two 

 broad-gauge systems. Leaving Mendoza, 

 where it connects with the Argentine 

 Great Western at a height of 2700 feet 

 above the sea, it turns southw-ard acro:-s 

 the plain, making for the point where 

 the Rio Mendoza leaves the eastern or 

 Uspallata range of the Andes, and then 

 follows the windings of the deep river 

 valley through the mountains. It thus 

 takes a route somewhat to the south 

 of that by which Darwin and other 

 travellers crossed this range. According 

 to their descriptions, the eastern slopes 

 are composed of Rhaetic sandstones and 

 bituminous shales resting on Devonian 

 and Ordovician slates, such as are found 

 in many parts of the Andes. These are 

 covered unconformably still further to 

 the westv.ard by thousands of feet of 

 acid and basic lavas and tuffs inter- 

 stratified with sandstones and carbon- 

 aceous shales, and believed to be of 

 Tertiary age. Intrusions of granite and 

 porphyry also occur. 



After emerging from these mountains 

 and traversing the Uspallata Pampa, a 

 plateau of coarse detritus at an altitude of 6000 feet, the 

 railway enters the central cordillera of the Andes by the 

 deep gorge of what may still be called the Rio Mendoza, 

 though, like most South American rivers, it is known by 



1 The illustrations are reproduced, with permi"wion, from a laper by Mr. 

 W. S. Barclay in ihe November number of the Geographical Journal. 



NO. 214.6. VOL. 8.%1 



different names in different parts of its course. Here Ihe 

 slates are covered apparently conformably by a thick 

 succession of Mesozoic rocks described in detail by Darwin, 

 Stelzner, and Schiller. They include acid lavas and tuffs, 

 breccias and conglomerates of the same material passing 

 into arenaceous rocks, amygdaloidal basalt, limestones, 

 gypsum interstratified with red and 

 purple sandstones and conglomerates, 

 and finally lava flows, tuffs, and con- 

 glomerates, consisting mainly of ande- 

 site, which are probably of late Creta- 

 ceous or even early Tertiary age. 

 Although marine fossils of Jurassic and 

 Cretaceous types are met with, some 

 of the beds were probably laid down 

 under continental conditions. On the 



east the rocks are much disturbed, and 

 are penetrated and metamorphosed by 

 granite and diorite, as well as by minor 

 inclusions, which traverse, not only the 

 stratified, but the plutonic rocks. 



The sides of the gorge present 

 magnificent sections of the geological 

 structure, one of the finest of which is 

 at the mouth of the Horcones valley, 

 by which AccMicagua was successfully 

 ascended. At Las Cuevas, a little 

 further on, the train enters the tunnel 

 beneath the Cumbre (" summit ") pass 

 and emerges in the valley of a tribu- 

 tary of the Rio Aconcagua, which 

 makes its way w-estward to the Pacific. 

 The tunnel is less than two miles long, 

 and little more than 10,000 feet above 

 the sea, while the pass is some 2000 

 feet higher. It is stated to have been 

 excavated in limestone and gypsum, 

 and conglomerates of rocks of igneous 

 origin. The western slopes of the ridge 

 are exposed to the wet north-west 

 winds, and the rocks are in places saturated with water 

 and decomjX)sed, so that it was necessary to face the 

 interior of the tunnel with concrete. 



The railway then follows the valley of the .\concagua, 



Fig. 2. — Scenerj- on the Chilian sidi of the tunnel. 



where the later volcanic rocks dip at moderate angles to 

 the westward, and are penetrated here and there by 

 intrusions of '* porphyry," down to the fertile plain of the 

 same name, where at Santa Rosa de los Andes it connects 

 with the State railways of Chile. On account of the 

 steepness of the valley slopes and the decomposition of 



