436 



Notes on the Influence 



[No. 36, 



running- streams of the north of Asia. It is ahnost useless to add 

 that under circumstances of this nature, the effect produced by the 

 simple evaporation of the rain water is not augmented ; on the con- 

 trary it ought to be rather less, for on a soil covered with plants wa- 

 ter will not so readily evaporate as on one destitute of vegetation. 



Again in the considerations I have supplied concerning the lakes 

 of Venezuela, of New Grenada, and of Switzerland, the disappear- 

 ance of a part of the flowing streams, which are tributary to these 

 lakes, might be attributed simply to a more limited fall of rain ; whilst 

 on the other hand, with quite as much reason it might be maintained 

 it was the consequence solely of the more rapid evaporation of the 

 rain water. Beyond doubt there are circumstances under the influ- 

 ence of which the diminution of the streams is the result simply of a 

 more active evaporation. I meant to have produced a good number 

 of examples bearing on this point. But in a discussion of this sort it 

 is not so much numerous as well authenticated facts, that it is impor- 

 tant to supply. Influenced by this consideration I shall limit myself 

 to the production of two facts ; the one derived from M. Desbassyn 

 ofRichemond, who observed it in the isle of Ascension; and the other 

 drawn from my own notes being one of the observations I made dur- 

 ing a sojourn of many years at the mines of Marmato. 



In the island of Ascension, a beautiful spring has been noticed si- 

 tuated at the foot of a mountain which was originally wooded, by de- 

 grees the spring was less copious, at length failed ; during tliis pro- 

 cess the forests were cut down and the mountain, was cleared. The 

 disappearance of the spring was attributed to the clearing. The 

 mountain was again planted, and after a few years the spring re-ap- 

 peared, became gradually more productive and finally was as copious 

 as ever. 



The metalliferous mountain of Marmato is situated in the province 

 of Popayan in the midst of immense forests. The stream of water 

 upon which the stampers are placed is formed by the union of many 

 small brooks which take their rise on the plateau of San Jorge. The 

 whole environs of the establishment are thickly studded with wood. 

 In the year 1826, when I for the first time visited these mines, Mar- 

 mato consisted of some miserable huts possessed by a few Negro 

 slaves. In 1830 the epoch at which I quitted this locality, Marmato 

 exhibited the most exhilarating appearance. There were now seen 



