220 nfFLUENCE OF THE FOEEST ON SPKINGS. 



two examples : one, wliere a fine spring, at the foot of a wooded 

 mountain in the Island of Ascension, dried up when the moun- 

 tain was cleared, but reappeared when the wood was replanted ; 

 the other at Marmato, in the province of Popayan, where the 

 streams employed to drive machinery were much diminished in 

 volume, within two years after the clearing of the heights from 

 which they derived their supplies. This latter is an interesting 

 case, because, although the rain-gauges, established as soon as the 

 decrease of water began to excite alarm, showed a greater fall of 

 rain for the second year of observation than the first, yet there 

 was no appreciable increase in the flow of the miU-streams. 

 From these cases, the distinguished physicist infers that very 

 restricted local clearings may diminish and even suppress 

 springs and brooks, without any reduction in the total quantity 

 of rain. 



It will have been noticed that these observations, with the ex- 

 ception of the last two cases, do not bear directly upon the ques- 

 tion of the diminution of springs by clearings, but they logically 

 infer it from the subsidence of the natural reservoirs which springs 

 once filled. There is, however, no want of positive evidence on 

 this subject. 



Marchand cites the following instances : " Before the felling of 

 the woods within the last few years, in the valley of the Soulce, 

 the Combe-es-Mounin and the Little YaUey, the Some furnished 

 a regular and sufficient supply of water for the iron works of Un- 

 terwyl, which was almost unaffected by drought or by heavy rains. 

 The Some has now become a torrent, every shower occasions a 

 flood, and after a few days of fine weather the current falls so 

 low, that it has been necessary to change the water-wheels, because 

 those of the old construction are no longer able to drive the ma- 

 chinery, and at last to introduce a steam-engine to prevent the 

 stoppage of the works for want of water. 



" When the factory of St. Ursanne was estabhshed, the river 

 that furnished its power was abundant, and had, from time im- 

 memorial, sufficed for the machinery of a previous factory. Af- 

 terwards, the woods near its sources were cut. The supply of 

 water fell off in consequence, the factory wanted water for half 

 the year, and was at last obliged to stop altogether. 



" The spring of Combefoulat, in the commune of Seleate, was 



