86 SAND-WASTES OP FRANCE. 



Landes the evil has been remedied by cutting rather deep drains to 

 carry oflf the water, and the roots of fern and other plants, which 

 partly perish every year, have been replaced by those of the maritime 

 pine. Thus the contamination of the air by the subsoil has been 

 stopped, and with it the intermittent fevers which had given to the 

 inhabitants a peculiar character of debility. M. Faye, after much 

 observation, arrives at what he believes to be a principle, namely, 

 that wherever an impermeable subsoil is found at a depth of two or 

 three feet from the surface there will always be intermittent fever if 

 the soil be contaminated by vegetable putridity, and fevers of a 

 typhoidal character if animal decomposition be present. As to the 

 remedy, it consists evidently either in draining, as adopted in the 

 Landes, or in the removal of the vegetable or animal decomposition." 

 But of this stratum. Marsh says : " The alios, which, from its 

 colour and consistence, was supposed to be a ferruginous formation, 

 appears from recent observations to contain little iron, and to owe 

 most of its peculiar properties to vegetable elements carried down 

 into the soil by the percolation of rain-water. See Revue des Eaux et 

 Forets, for 1870, p. 301." 



Whatever the source of the material and the process of its forma- 

 tion, the effects of its presence on the moisture of the sand-wastes 

 and on vegetation there is great. 



And from what has been advanced it appears that, in so far as 

 moisture is concerned, dunes and sand plains are not always so 

 devoid of water as they seem, and as the common expression Dry 

 Sand would suggest. 



Marsh, in connection with a remark made by himself, in which he 

 says in regard to sand hillocks : " it is observed that from capillary 

 attraction, evaporation from lower strata, and retention of rain-water, 

 they are always moist a little below the surface," cites in a foot-note 

 the following observations : " Dunes are always full of water, from 

 the action of capillary attraction. Upon the summits one seldom 

 needs to dig more than a foot to find the sand moist ; and in the 

 depressions fresh water is met with near the surface. Forchhammer 

 in Leonhard und Broun for 1841, p. 5. 



" On the other hand, Andresen, who has very carefully investi- 

 gated this as well as all other dune phenomena, maintains that the 

 humidity of the sand ridges cannot be derived from capillary 

 attraction. He found by experiment that a heap of drift sand was 

 not moistened to a greater height than eight and a half inches, after 



