88 M. Boussingault on the -Effect of clearing' Land 



Geologists have observed, that in every region of the globe 

 the level of the waters has undergone marked variations, whe- 

 ther as it respects the coasts of the ocean, or the margin of 

 great lakes. The fact is certain, and is now questioned by no 

 one. There is not, however, the same unanimity as to the cause 

 of the phenomenon. Some, and these the greater number, 

 maintain that in most cases the change of level is only appa- 

 rent, and that the masses of water have in no degree sunk, but 

 that the shores have been uplifted. Others, again, recognise 

 in the phenomenon a real diminution of the liquid mass, — a 

 true drying up. Both of these parties adduce various reasons 

 in support of their several hypotheses. On this occasion, how- 

 ever, we are not called to enter upon this geological disputation. 

 We shall have nothing to do with the sea-coasts ; nor shall we 

 any more regard those great differences in the level which have 

 evidently occurred in some lakes, as the result of certain geo- 

 logical causes which are quite foreign to our present subject. 

 These variations, which are often very great, appear in gene- 

 ral to have been occasioned by violent catastrophes, which 

 have occurred anterior to the era of history. I shall make use 

 then, only of those changes in the levels of lakes which have 

 been observed by our ancestors, or our contemporaries ; or, in 

 other words, I shall regard as valuable those events only which 

 have happened under the inspection of mankind, and this, be- 

 cause it is the effect of their agricultural labours upon the me- 

 teorological state of the atmosphere, that I wish to appreciate. 

 America has been the principal site of the observations which 

 follow ; whilst at the same time it will appear that what is true 

 respecting the New world, is no less applicable to the Old. 



It will not be disputed that one of the most interesting dis- 

 tricts of the kingdom of Venezuela is the valley of Aragua, si- 

 tuated at no great distance from the coast, possessing a warm 

 climate, and a fertility of soil which can scarcely be surpassed. 

 In it we observe every species of cultivation which distinguishes 

 the tropics ; and upon the lesser hills which rise from the val- 

 ley, we observe with astonishment crops which remind us of 

 European farming : corn grows admirably upon the heights 

 which surround Vittoria. The valley is bounded on the north 

 by the high land wliich forms the coast, on the south by the 



