12 



More about the clay 



and rose 1*91 millimetres between September 7th 

 and 19th of the same year, much rain having fallen 

 during the latter part of this time. During frosts and 

 thaws the movements were twice as great." 



You must have found out by now how very slippery 

 clay becomes as soon as it is wet enough. It is not 

 easy to walk over a clay field in wet weather, and if the 

 clay forms part of the slope of a hill it may be so slippery 

 that it becomes dangerous. Sometimes after very heavy 

 rains soil resting on clay on the side of a hill has begun 



Fig. 5. 



Clay swelling up when placed in 



water and overflowing from the 



egg-cup into which it was put 



to slide downwards and moves some distance before it 

 stops. Fortunately these land slips as they are called, 

 are not common in England, but they do occur. Fig. 6 

 shows one in Devonshire, and another is described by 

 Gilbert White in The Natural History of Selborne. 



Another thing that you will have noticed is that 

 anything made of clay holds water. A simple way of 

 testing this is to put a round piece of tin perforated 



