100 M. Boussingault on the Effect of clearing Land 



Saussure admits that, at an epoch much anterior to the times 

 of history, the mountains which surround the lake were buried 

 under water. Some vast catastrophe occasioned a great dis- 

 ruption, and speedily the current of waters occupied no greater 

 space than the bottom of the valley : in short the Lake of 

 Geneva was then formed. But turning from this to the monu- 

 ments which have been constructed by man, it is impossible to 

 doubt that, during the course of twelve or thirteen centuries, 

 the waters of the Lake of Geneva have considerably retired. 

 This is evident from the flat shores it has left near its margin ; 

 and even in the town itself, the Quartier de Rive, and the low 

 streets, have been built upon such sites. This lowering of the 

 surface, continues Saussure, is not the result only of the wear- 

 ing down of the channel whence its waters issue, it has likewise 

 been produced by a diminution of the quantity of the waters 

 which flow into it. The general residt which may be safely drawn 

 from the observations of Saussure is, that during the pei'iod of 

 twelve or thirteen centuries, the running streams have gradually 

 diminished throughout the districts in the neighbourhood of the 

 Lake of Geneva. And there is no one, I believe, will dispute that, 

 during that long period, there has been vast clearing away of 

 wood, and a rapidly increasing advance in the cultivation of this 

 beautiful country. Upon the whole, by the examination of the 

 levels of lakes, we have arrived at this conclusion, that in those 

 countries which have been extensively cleared, it appears very 

 probable that there has been a diminution of the running 

 streams which flow through the district ; whilst, on the other 

 hand, where no great change has been effected in this way, the 

 streams have been subjected to no variation. 



Great forests, therefore, in the point of view we are now re- 

 garding them, appear to have the effect, first, of preserving 

 the volume of water destined for the use of machines and of 

 canals, and then to be an obstacle to the rain water collecting 

 and running off" with too much rapidity ; being at the same 

 time an obstacle to evaporation. That a surface covered with 

 trees will not be so favourable to evaporation as a well wooded 

 one, is what every one will admit, without discussion. But 

 that the difference of these two conditions may be adequately 

 appreciated, it is necessary that the traveller should successively 



