1899. ] Climbs and Explorations in the Andes. 189 



WEEKLY EVENING MEETING, 



Friday, May 26, 1899. 



The Right Hon. The Earl of Halsbuky, M.A. D.C.L. F.R.S., 

 Lord Chancellor, Manager, in the Chair. 



Sir William Martin Conway, M.A. 



Climbs and Explorations in the Andes. 



[Abstract ] 



The object of my journey to South America, made in the latter part 

 of 1898, was to investigate the physical geography of the Cordillera 

 Real in Bolivia. I was accompanied by two Alpine guides, Antoine 

 Maquignaz and Louis Pellissier. The Cordillera Real is a snowy 

 range eighty miles in length, culminating at its north end in Mount 

 Sorata and at the south in Illimani. It is not a volcanic range, nor 

 were any signs of volcanic action met with at any part of its main 

 axis. It consists principally of a core of crystalline rock, flanked to 

 the westward by Silurian deposits and further out by Red Sandstones 

 and Conglomerates, rising in low hills out of the plateau which 

 stretches all along the foot of the range at an altitude of between 

 12,000 and 13,000 feet above the sea. This plateau was formerly 

 the bed of a large inland sea, of which there only now remains the 

 relatively small portion known as Lake Titicaca. 



The two great peaks, Illimani and Sorata, were ascended, Illimani 

 to its highest point, Sorata to within a couple of hundred feet or so 

 from the top. At both ends the range is cut through by river valleys 

 which drain to the eastward. That to the south is the valley of the 

 La Paz River, which, rising on the slope of Mount Cacaaca, the 

 midmost peak of the range, flows first to the south-east along 

 the range, and then cuts right across it and flows into the River Beni, 

 a tributary of the Amazon. To the north the sources of the Mapiri 

 River lie actually at the foot of Mount Sorata, and some of the snow- 

 slopes, belonging properly to the western face of the mountain, drain 

 into it. But the actual cutting through of the range is not here 

 complete. There still remains a low ridge, ahout 2000 feet higher 

 than Lake Titicaca, which is not entirely cut through, though the 

 eating-back process is going forward very rapidly, and the day is not 

 far distant from a geologist's point of view when Lake Titicaca must 

 be drained by this river. 



The eastern face of the range was not visited on this journey. 

 On the west the line of great mountains is flanked by vast slopes of 

 debris, and here the signs of former glacial extension are easily 



