92 SAND-WASTES OF FRANCE. 



that vegetation can be extended over sand-wastes — even moisture 

 existing there. 



The alios is met with in the sands of the Landes of the Gironde, 

 at a depth of about three feet below the surface. It is often about a 

 foot in thickness, and underneath this is sand of unknown depth. 

 Diggings have been made to a depth of upwards of 60 feet without 

 reaching other material. In the winter season these Landes are 

 covered with water which has no fall, and cannot sink through this 

 layer ; but in summer neither pool nor moisture is to be seen, the 

 water having been evaporated, and the layer preventing an ascent of 

 moisture from below. But, as has been intimated, there are spots 

 where this stratum is awanting or has been broken, and on these 

 grow bushes and trees, the ground neither being drenched in winter 

 nor altogether devoid of moisture in summer. 



Both in connection with notices of the drift sands of the Landes on 

 the coast, and of the sand-wastes of La Sologue, mention has been 

 made of peat lands and of marshes. These are found on sand-wastes 

 in so many lands that the existence of them in such lands appears to 

 be the rule, and the absence of them the exception. Suffice it here to 

 state that a sand ridge may pi'event escape of the waters by flow, 

 and a stratum of alios or ortstein, or clay, or other impervious substance, 

 may prevent escape by percolation. 



From the treatise by Herr Wessley entitled, Der Europaische 

 Flugsand und seine Kultur already cited, much information may be 

 gathered in regard to the composition and condition of the sand- 

 wastes of Europe. 



In regard to the general appearance and composition of the drift 

 sands of Europe, he says that in all places they consist in a vastly 

 preponderating degree of fine somewhat rounded grains of quartz, 

 with which only a small percentage of other materials are com- 

 mingled. 



The admixture consists primarily of felspar, which in old sand has 

 for the most part experienced the disintegrating and decomposing 

 efi'ects of weathering, of lime, mostly fragments of shells ; of mica ; of 

 magnetic, or Titanian ironstone ; and finally, of difierent other 

 minerals, hornblend, augite, hypersthen, basalt, and carbon. 



The separate grains are more or less covered with a fine mould, 

 on which depends next the fertility of the drift sands. For this 

 depends in general on an admixture of products of the weathering 

 just spoken of, or on those which the sand, the natural vegetation 



