24 Some experiments with the somd 



other places are fields where so much of the soil is blown 

 away by strong winds that the crops may suffer injury. 

 In Central Asia sand storms do very much harm and have 

 in the course of years buried entire cities. Fig. 12 shows 

 the Penhale sands in Cornwall gradually covering iip 

 some meadows and ruining them. 



Sand particles, being large, do not float in water. If 

 we shake up sand in water the sand sinks, leaving the 

 water entirely clear. So running water does not carry 

 sand with it unless it is running very quickly : the sand 

 lies at the bottom. 



Unlike clay, sand does not hold water. Pour some 

 water on to sand placed on the tin disk in a funnel 

 (Fig. 8) ; it nearly all runs through at once. We should 

 therefore expect a sandy field or a sandy road to dry up 

 very quickly after rain and not to remain wet like a clay 

 field. So much is this the case that people prefer to live 

 on a sandy soil rather than on a clay. The most desir- 

 able residential districts round London, Hampstead on 

 the north, and the stretch running from Haslemere on 

 the south-west to Maidstone on the south-east, and other 

 favoured regions, are all high up on the sand. 



At the foot of a hill formed of sand you often find 

 a spring, especially if clay or solid rock lies below. It 

 is easy to make a model that will show why the spring 

 forms at this particular place. Fill the lower part of 

 the box shown in Fig. 13 with wet clay, smoothing it 

 out so that it touches all three sides and the glass front ; 

 then on top of the clay put enough sand to fill the box. 

 Bore four holes in the side as shown in the picture, 

 one at the bottom, one at the top, one just above the 

 junction of the sand and clay, the fourth half way up the 

 sand, and fix in glass tubes with clay or putty. Pour 



