102 iM. Boussingault on the Effects of' clearing Land 



water. In the latter case again, that is to say, where a great 

 extent of uncultivated land shall have been reclaimed, there 

 will be an evident consumption of water by the vegetation 

 which has been there promoted ; and the introduction of agri- 

 cultural industry will, under these circumstances, tend to di- 

 minish the water-courses which traverse the country. It is 

 very probable that we are to attribute to this circumstance the 

 gradual drying up of the lakes which to a certain extent gauge 

 the running streams of the north of Asia. It is almost useless 

 to add, that, under circumstances of this nature, the effect pro- 

 duced by the simple evaporation of the rain-water is not aug- 

 mented ; on the contrary, it ought to be rather less, for on a 

 soil covered with plants water 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 

 disappearance 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 influence 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 important to supply. Influenced by this consideration, 

 I shall limit myself to the production of two facts ; the one de- 

 rived from M. Desbassyns of Richemond, who observed it in 

 the isle of Ascension ; and the other drawn from my own notes, 

 being one of the observations I made during a sojourn of many 

 years at the mines of Marmato. 



In the island of Ascension a beautiful spring has been no- 

 ticed situated at the foot of a mountain which was originally 

 wooded ; by degrees the spring was less copious, — at length 

 failed ; during this process 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 reappeared, be- 



