32 



Some experiments vnth the scmd 



swell on wetting, and you will find nothing happens 

 when you try with sand the experiment with the model 

 field (p. 11) or the egg-cup (p. 12). 



Fig. 18. 



The roads round Wye. As far as possible they keep off the clay (the 



plain part of the map) and keep on the chalk or the sand (the 



dotted part of the map) 



