84 



FIRST YEAR SCIENCE 



Water getting into the. cracks of rocks and expanding 

 when it freezes splits them apart and aids much in their 



destruction. Plant 

 roots penetrate into the 

 crevices of rocks and by 

 their growth split off 

 pieces of the rock. 

 Water, especially when 

 it has passed through 

 decaying vegetable mat- 

 ter, has the power of 

 dissolving some rock 

 minerals. Certain min- 

 erals of which rocks are 

 composed change when 

 exposed to the air some- 

 what as iron does when 

 it rusts. 



Where the temperature varies greatly during the day 

 the expansion and con- 

 traction due to the heat- 

 ing and cooling some- 

 times cause a chipping 

 off of the rock surfaces. 

 In some localities, the 

 winds, by blowing sand 

 particles against the 

 rocks, cut them away 

 quite rapidly. All these 

 agencies and others tend 

 to break up and decom- 

 pose the rocks, thus 

 forming soil. The actions of some of these agencies were 

 seen in the previous experiments. 



ROCKS SPLIT BY ROOTS OF A TREK. 



WIND-CUT ROCKS. 



These rocks have been fantastically cut 

 by wind-blown sand. -, 



