94 SAND-WASTES OF PRANCE. 



The coherence of sands of varied composition, as determined by 

 Schuebler and others, give the following result : 



" Taking perfectly dry, pure quartz sand as zero, a mixture of 4 per 

 cent, of water gives it so much consistency that it may be pressed in 

 the hand and cease to be driven of the wind ; and this latter result 

 follows an admixture of 4 per cent, of clay or 16 per cent, of lime, 

 or 10 per cent, of humus. But what is thus gained by an admixture 

 of humus, clay or lime, is lost by its being frozen in a moist state, 

 on its being thawed, a peculiarity which it shares with all soils. 



This, if it be so, may be attributable to the affinity of these sub- 

 stances for moisture, of which sand has little or none, leading to their 

 absorbing all the free moisture, and leaving the quartzose sand dry 

 and free to be blown away. 



The commixture of lime and of clay with sand, so beneficial to 

 the latter, has also this bad effect when it is considerable — that after 

 heavy rains, followed by rapid desiccation, sometimes there is left 

 on the surface of the sand a crust detrimental to vegetation. 



Pure sand does not shrink in bulk in drying. 



The following table, prepared in accordance with observations re- 

 ceived by Schuebler, will make apparent the difference between pure 

 sand and other earthy matters : 



Pure sand loses in bulk in drying, 



Fine carbonate of lime, 



Pure clay, 



Humid acid, ... 



Field earth, ... 



Garden earth, 



The latter numbers are indicative of there being contained in these 

 bodies, as found on sandy regions, an admixture of humus or of clay. 



Eeference has been made to the effect of moisture in arresting and 

 in preventing the -drifting of sand. In view of the effect of heat in 

 desiccating sand, arid also in view of the effect of temperature on 

 vegetation, the degree in which the properties of absorbing and 

 of transmitting heat are possessed by sand deserve consideration. 



The following results of experiments by Schuebler show the com- 

 parative capability of becoming heated possessed by sand. In the 

 month of August, with an atmospheric temperature in the shade of 

 from 22° to 25° K., 81° to 88° Fahr., the temperature of the following 

 substances exposed to the bright sunshine were, according to the 

 scale of Keaumeur : 



