EFFECT OF HEAT OX MATTER 



IV 



irresistible. This effect is most conspicuous in rocky 

 or mountainous regions. Here massive rocks are some- 

 times pried out of position, and large and small 

 particles of rock are broken off. This is the origin of 

 a large part of the debris brought down the mountain 

 slopes by the spring rains. 



Water pipes, in cold places, are burst in a similar 

 fashion. Parts of cement walks are sometimes dis- 



Fig. 9. A solid concrete silo cracked by uneven contraction and 

 expansion caused by extreme cold and extreme heat. 



placed, bricks and even fence posts are likewise 

 frequently pushed out of place by the action of freez- 

 ing water in the soil. 



