1S49.] exercised by Trees on Climate. 431 



thick forests which are ahnost impenetrable. I note this circum- 

 stance, because I have the strongest conviction that an extensive 

 clearing of wood were it to take place even on a lower level than an 

 alpine lake, and at a considerable distance from it, would still exert 

 an influence over the mean level of its waters. 



We may here also notice, without removing from the locality we 

 have thus introduced to notice, the singular lake of Cuicocha, which 

 occupies a trachytic basin in which two islands, which have been ex- 

 amined with much care by Colonel Hall, attest the stability and the 

 uniformity of its level. The study likewise, of the lake Yaguar- 

 cocha, or the lake of blood, so designated since Huayna-capac dyed 

 its waters wdth the blood of 30,000 Canra 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 show by this selection that, as I remarked at the commence- 

 ment of this discussion, those observations wdiich are made upon 

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

 fect we might expect to be produced by a stream issuing from a lake 

 is, that the stream would deepen its furrow and consequently lower 

 the waters. I have, however, observed that in spite of this circum- 

 stance 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. 



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

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

 cause it has been accurately examined at two epochs, which are suf- 

 ficiently distant from each other, the one being the year 1740 on the 

 other 1831. 



In travelling to Latacunga, a town situated at no great distance 

 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 

 envelop the shrubs on its edge ; and it likewise produces frequent 

 detonations which are heard at a great distance. These statements 

 were more than sufficient to induce M. de la Condamine, who was 

 at Latacunga in September, 1738, to undertake an excursion to 



