36 CLIMATE AND RESOURCES OF 



appearance and almost the density of sandstone. On digging 

 into the sandhills we always find moisture present at a little 

 depth below the surface : this water is not retained by resting 

 on a stratum of clay or other impervious soil. If retained by 

 an impervious stratum, we must suppose it to form a saucer- 

 shaped depression, or escape of water would take place from 

 its lower side. But these sandhills are elevated above the 

 surrounding country, and there is no other way of accounting 

 for their retaining water than by capillarity. Jheels, or 

 swamps at the base of a range of sandhills, are fed by springs 

 with water throughout the year, and never dry up, showing 

 that all excess of water, beyond what can be held by capil- 

 larity, escapes by percolation. 



Dunes occur in Europe, chiefly on the seashore; and cen- 

 turies ago care was taken to encourage the growth of grass, 

 chiefly the Arundo arenaria, on them. This grass binds the 

 sand, and prevents its further drifting, and covering the 

 neighbouring country. 



Of such importance was this considered, that according to 

 Marsh, in 1539, a decree of Christian III., King of Denmark, 

 imposed a fine upon persons convicted of destroying certain 

 species of sand-plants upon the coast of Jutland. This ordi- 

 nance was renewed in 1558 ; and in 1569 the inhabitants were 

 required to do their best to check the sand-drifts. In 1779 

 planting the Arundo arenaria and other sand-plants, and the 

 exclusion of animals destructive to them, was adopted as a 

 system. " Ten years later plantations of forest trees, which 

 have since proved so valuable a means of fixing the dunes, and 

 rendering them productive, were commenced, and have been 

 continued ever since." 



The planting of seashore dunes has been carried out in all 

 European countries where they exist; the tree found most 

 useful and best adapted for them being the Pinus maritima. 



