WIND. 21 



and they not unfrequently play a prominent part in choking up 

 bays, estuaries, or river channels. 



The rapidity with which such drifts will sometimes form 

 banks against or around objects impeding their course is remark- 

 able ; and the advance of foreshores is often much accelerated by 

 the accumulations thus deposited about piers or jetties which 

 cross sandy shores. 



On many coasts notably those of France and Africa the 

 expenditure incurred in arresting these sand-drifts has been very 

 large. The object aimed at is to prevent the sand being blown, or, as 

 it is termed, to " fix " it, for a sufficient length of time to admit of the 

 growth of vegetation in such luxuriance as to form a natural covering 

 to the surface, and so protect it from the wind. 



The system usually adopted is that of spreading cut brushwood 1 

 over the whole area of the drift commencing, as a matter of course, 

 at the windward end and sowing the seed of various suitable plants. 



Sometimes the brushwood, instead of being used to cover the 

 surface, is employed in forming artificial hedges or " breakwinds." 

 These are constructed by sticking the brushwood into the sand, so as 

 to form parallel hedges about 4 feet in height. They are generally 

 placed from 10 to 12 feet apart, and run at right angles to the course 

 of prevailing winds. Seeds of different trees, and of various suitable 

 plants and grasses, are then sown and raked in, young trees being 

 also planted. 



At the Cape of Good Hope, aloes, cut down and stuck into the 

 sand, quickly take root, and form excellent hedges. Where these 

 cannot be obtained, brushwood which retains its leaves when dead 

 should be selected. 



Care must be taken that the sowing of seeds and planting of 

 trees is carried on at the right season. 



The system of forming hedges is more costly than that of merely 

 spreading the brushwood, but it possesses the great advantage of 

 affording protection to young plants and trees until they have acquired 

 sufficient strength to take care of themselves. 



Sometimes palisades formed of planks are used, the planks 

 being driven sufficiently far into the sand to give them stability, and 

 being spaced so as to allow openings of two or three inches between 

 them. A bank of sand quickly collects on the leeward and windward 

 sides of such barriers, and if, as the height of the bank increases, the 

 boards be raised by drawing them a few feet at a time, very large 

 quantities of sand may be thus arrested, and high mounds formed. 



1 In some instances town refuse has been employed with advantage. 



