CATARACTS AND INUNDATIONS* 7 



Aure, is the nature of the soil through which they pass. M. Guet- 

 tard has observed that it in general porous, and composed of a thick 

 sand, the grains of which are not well compacted together ; it sinks 

 suddenly down by its own weight in some places, and there forms 

 great holes; and when the water overflows the meadows, it fre- 

 quently makes many cavities in several parts of them. If we there- 

 fore suppose inequalities in the channels of these rivers, and that 

 there are certain places in which the water stagnates longer than in 

 others, it must there dilute the ground, if we may use that expres- 

 sion ; and having carried away the parts which united the grains of 

 sand together, those grains will become afterwards no other than a 

 kind of sieve, through which the waters will filtrate themselves, pro- 

 vided nevertheless that they find a passage underground through 

 which thev may run. This conjecture appears to be so well founded, 

 that each of these three rivers loses itself nearly in the same man. 

 ner, that is, through cavities which the people of the country call 

 betoirs, and which swallow up more or less according to their large- 

 ness. M. Guettard, who has carefully examined them, remarks, that 

 these betoirs are holes in the form of a tunnel, whose diameter and 

 aperture is at least two feet, and sometimes exceeds eleven; and 

 whose depth varies in like manner from one and two feet, to five, 

 six, aud even twenty. The Rille during the summer season loses 

 almost all its water in the space of two short leagues; the Ithon 

 does very near the same. But M. Guettard observes something 

 curious concerning this river, that formerly it was not lost, but kept 

 its course without any interruption, as appears by the history of the 

 country ; very likely the mud, which had been collected together in 

 several parts of its channel, might have occasioned the waters re. 

 rnaining in others, and have caused many betoirs. This is the more 

 likely, as the mud having been collected together in the bed of the 

 river Aure, it appears that, in consequence, the cavities were greatly 

 increased, which makes it lose itself much sooner than formerly. 

 Besides, possibly an earthquake happening in the country might have 

 caused several subterraneous canals through which the water of the 

 Ithon has forced its way. In effect, it appears, that a soil's being 

 porous is not sufficient to cause the loss of a river ; for if it was, 

 then to do so it would occasion many fens round about, nor would 

 it renew its course after having disappeared a certain time; it must 



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