1885.] SAND-PLAINS OF BELGIUM. 199 



been here brought under consideration, may bo seen the consum- 

 mation of the purpose. 



"Wliere barriers of massive architecture, raised to no inconsiderable 

 height, might liave failed, this simple operation has proved effectual. 

 Sand-hills may often be seen travelling onward in a mass. Such 

 advancing masses have without a pause swallowed np houses which 

 stood in their path, passed over them, and advanced on their way, 

 leaving them behind. I have had occasion ,to study the pheno- 

 menon of a house coming out to windward of an immense sand- 

 wave by which it had been engulfed within the memory of some of 

 my informants, — engulfed by the leeward side of the advancing 

 wave. In this case, and in every such case, the mass of sand 

 advances like boys advancing in the game of leap-frog : in this one 

 boy leaps over in succession the backs of a nmnber of others ; then, 

 stooping in front, each of them in succession does the same, vaulting 

 over him as over the others, and taking up a position in front of 

 all ; and this goes on continuously till they determine to cease. So is 

 it on a larger scale with the advancing sand-wave : each — particle by 

 particle, all in succession — rolls up the windward slope, passes over 

 the crest, rolls down the leeward slope, and rests, till all in succes- 

 sion have done the same. Should they encounter a barrier ■which 

 is not insurmountable, the sand accumulates to windward till it 

 forms an inclined plain of the angle of stability, reaching from the 

 ground to its summit, and then passes on. The hopelessness of 

 any attempt permanently to arrest the onward progress of a sand- 

 hill by an opposing barrier may begin to be apparent. But what 

 cannot be done by erecting an obstacle, may be accomplished quietly 

 by binding the particles before they begin to move. Thus can the 

 guardian of the peace pin down and hold fast and keep down the 

 desperado in a passion ; thus can the sick-nurse or attendant on a 

 patient suffering under the delirium of a fever control the struggle 

 of the sufferer : but in either of these cases could the subdued man 

 get his hand loose and his arm free, he might get upon his feet, and 

 once upon his feet with hand loose and arm free, all restrictions put 

 upon him might prove powerless as the green withes with which 

 Samson was bound. 



Upon this principle is it that drift-sands are arrested and sand- 

 dunes are fixed and utilized. There are several vegetables which 

 find a soil appropriate for their nourishment and growth in sand ; 

 by the rootlets of these, as well as by the shelter from the wind 

 which they afford, tlie sand is enmeshed and held fast ; and when 

 the vegetable soil is increased by the decay of these or otherwise, 

 bushes, shrubs, and trees may germinate and grow, consolidating and 

 sheltering more completely the mobile sand. And thus may be 



