in diminishing the Quantity of Water in Rivers. 97 



30,000 Canara Indians whom he there slaughtered, would lead 

 to a similar result. Neither of these lakes have any outlet. 

 Instead, however, of dwelling upon them, I shall in preference 

 select Chilcapan lake, and especially because it has a natural 

 issue towards the north, whence rises the river Blanco. I wish 

 to shew by this selection that, as I remarked at the commence- 

 ment of this discussion, those observations which are made upon 

 bodies of water with such outlets are not to be neglected. The 

 effect we might expect to be produced by a stream issuing from 

 a lake is, that the stream would deepen its furrow, and conse- 

 quently lower the waters. I have, however, observed that, in 

 spite of this circumstance, the level of Lake Chilcapan has not 

 been sensibly lowered. In attentively examining the trachytic 

 rock in the spot from which the river Blanco takes its rise, I 

 have not been able to recognise any indication of the water 

 producing an eroding effect. It is also true that, in the nume- 

 rous cascades which I have likewise examined, I have found 

 that a mass of water, by being precipitated rapidly, wears away 

 the hardest rocks. But I repeat, that I have not been able to 

 observe that the wearing effect of the water was at all appre- 

 ciable when it flowed steadily over a rock, and when the water 

 current did not draw along with it, as is very generally the 

 case in mountain streams, pebbles, whose continual friction 

 can scarcely fail to wear the surface of the rock over which 

 they glide. 



I shall conclude what I have to observe concerning the lakes of 

 South America by a few remarks upon the one called Quilatoa, 

 because it has been accurately examined at two epochs, which 

 are sufficiently distant from each other, the one being the year 

 1740, and the other 1831. 



In travelling to Latacunga, a town situated at no great dis- 

 tance from Cotopaxi, a great deal is often heard of the wonders 

 of the Lake of Quilatoa. From time to time this lake throws 

 out flames, which envelope the shrubs on its edge ; and it like- 

 wise produces frequent detonations, which are heard at a great 

 distance. These statements were more than sufficient to in- 

 duce M. de la Condamine, who was at Latacunga in Sep- 

 tember 1738, to undertake an excursion to it. He found 

 it was almo.st circular, with a diameter of about 400 yards. 



VOL. XXIV. NO. XLVII.— JANUARY 1838. G 



