OF ARTS AND SCIENCES. 289 



and those back of Juli ; while from the lower lake, back of Aygache, 

 the lake formed huge inlets or deep bays, now represented only by 

 the nearly dry river-beds flowing into the lake at Aygache, Gorilla, 

 and Guajui. The sluggish Desaguadero must have been a strait of 

 considerable width, with large islands ; and this long lake, connecting 

 Lake Titicaca with Lake Aullagas, must have equalled in extent the 

 upper lake ; the upper lake, at that time, extending across the Isth- 

 mus of Yunguyu, leaving the Peninsula of Copacabana as a large 

 island, connected with the lower lake by a broad pass between the 

 hills to the west of Copacabana, and those to the west of Yunguyu. 

 The plains, now laid bare at the northern and western shores of Lake 

 Titicaca, give us an excellent idea the appearance the whole basin of 

 the lake would present if entireh'^ dry. The number of lakes and 

 basins, great and small, which formerly covered the elevated plateau 

 of the Andes, must have been very great ; but we now fiiid only 

 here and there a small sheet of water. The former lakes are only 

 rejiresented by the more or less extensive pampas, forming basins at 

 great altitudes, showing plainly that the whole of this district is re- 

 ceiving a much smaller waterfall than in former times, but probably 

 not within historic times, if we take into consideration the position 

 of some of the most ancient ruins of Bolivia (at Tiahuanaco), which 

 are only about 75 feet above the present level of the lake. These 

 ancient basins are thickly covered by huge bunches of rank grass, 

 from which the llamas, alpacas, and vicunas obtain their only suste- 

 nance at the immense heights where they seem best to prosjier. It 

 would be an interesting inquiry to ascertain the causes of the differ- 

 ence in the habitat between the other species of camels and the 

 llamas, which do not thrive near the sea-coast. 



In the lower lake, which is shallow, the temperature of the surface 

 and that of the bottom varied extremely. From the number of obser- 

 vations taken, I can only state that it is very local, depending upon 

 the prevailing wind and the condition of the sky. 



The following soundings, taken from those of the upper lake, show 

 the great uniformity of the temperature of the surface and bottom: — 



VOL. XI. (N. S. III.) 19 



