Lake Titicaca. 427 



200 miles, and Pniio, the middle point, lies in that great 

 depression, or table-land, hung between the two Cordille- 

 ras, and extending from the sources of the Ucayali to be- 

 yond Oruro. It is apparently a volcanic basin ; frag- 

 ments of lava, porphyry, and jasper are scattered around 

 the lake ; and towers of igneous rocks protrude through 

 the sedimentary strata. It has an area of 16,000 square 

 miles, and an oval shape with the small end near Oruro, 

 an average width of one hundred miles, and a southerly 

 slope. ' 



Titicaca,* the largest lake in South America, has about 

 half the size of Ontario. It spreads over 2500 geograph- 

 ical square miles, being one hundred miles long, with an 

 average breadth of twenty-five miles. The water is slightly 

 brackish. It never freezes over, though ice forms in shal- 

 low places. The chief feeders of the lake are the Mara- 

 villas, Ramis, and Azangaro, the Rarais rising in a pond, 

 or tarn (La Raya), which is also the source of a tributarj- 

 to the Ucayali ; so that a cork thrown into this pond might 

 find its way to the Amazons or Titicaca, according to the 

 direction of the wind. The water of the lake is drained 

 off by the Desaguadero, and disappears in the swampy la- 

 gune of Aullagas. The lake is gradually filling up, for 

 there is no vegetation on the surrounding hills to prevent 

 the rains from washing down the soil. The most sedi- 

 ment enters at the north end ; at the south, the water is 

 noticeably clearer. The surface of the lake is also sinking. 

 Three hundred years ago, its waters washed the ancient 

 monuments of Tiahuanaco, now twelve miles distant from 

 its shores, and 130 feet above it. In 1827, Pentland made 

 its altitude 12,795 feet, and its area nearly 4000 square 

 miles. Now we know that the true level of the lake at 

 high-water mark is only 12,493 feet, as determined by the 



* An Aymaia word signifying "cat-rock." 



