DRIFT-SANDS AND THEIR FORMATIONS. 539 



Fortunately, it is only the dry sand that is destitute of cohesion. 

 Were this not the case, a whole dune might be taken up and re- 

 moved to another spot during a very heavy storm. Sand possesses 

 considerable capillarity, by virtue of which the ground-water at 

 its bottom rises through its substance ; so that an apparently dry 

 dune is so moist only a few feet below its surface, as to form a 

 compact mass. Rain, however, only temporarily lends it a certain 

 degree of fixedness. The air present between the grains of sand 

 permits to rain-water a slow percolation, so that it has been ob- 

 served, particularly with fine sand, that water ascends in it from 

 below more rapidly than it descends from above. Rain-water, not 

 being all sucked up by the sand, has to run down the slope, and, 

 therefore, not rarely washes deep furrows in the mass. Sand that 

 has been moistened by rain is more tractable after drying than be- 

 fore it was wet, because the interposition of the water has sepa- 

 rated the grains, and they are more easily moved by the wind. 

 The wind can only wear away the surface of a dune. It therefore 

 takes the direction of the ascent of the dune, and carries the sand 

 with it. A space free from wind is formed upon the top of the 

 dune, where the larger grains fall upon the ground and run down 

 on its other side, forming a nook in which they are enabled by 

 their cohesion to remain, while the finer grains are carried farther 

 by the wind. The dunes thus maintain their general forms while 

 slowly advancing. The progress of the dunes has been frequently 

 observed, and attempts have been made to measure it. A series 

 of observations for twenty-three years in the barrens of the Ba- 

 nat gives an average of two metres a year. It is estimated, ac- 

 cording to Count Adelbert Baudissen, on the island of Sylt, that the 

 dunes are moving from west to east at the rate of four metres a 

 year. Hagen names a rate of five and a half meters a year for two 

 dunes on the Friesian lowlands, and Krause, four metres a year for 

 another one. Elie de Beaumont describes dunes in Brittany that 

 have moved since 1666 at the rate of seven metres a year; and 

 Behrendt gives the average annual progress as from five to six 

 metres. 



A traveling dune is stopped by no obstacles. With the irresisti- 

 bility of an element only slower than water or fire, it presses for- 

 ward, burying field and wood, and even whole villages. The 

 spires of church-towers may still be seen projecting out of the 

 sandy sea of Brittany, testifying to the presence of former dwell- 

 ing-places, there. The whole northern point of Jutland has been • 

 given up by man to the advancing sand. 



In the seventeenth century an old churchyard was found, over 

 which a dune had taken its course, on the Courland lowlands 

 north of Kranz. A sandhill that separated the hamlet Sarkan 

 from the parish- village Rositte, and which had to be crossed by 



