6 



THE SOIL AND ITS ORIGIN 



Rock Weathering the Soil-forming Process. The formation 

 of soil is the result of the slow process of rock weathering, meaning 

 the breaking up and decay of rocks brought about by the destruc- 

 tive action of the forces of nature. These forces include : 



(a) HEAT and COLD causing cracking and splitting of rocks 

 through sudden temperature changes. 



(6) FROST causing splitting and cracking by freezing water. 



FIG. 2. Sugar Bowl Rock, Dells of the Wisconsin River. 



disintegrate rocks. 



Water wears away and helps to 



(c) WIND causing abrasion through the action of dust and sand 

 particles carried by it. 



(d) ICE causing grinding as in glacial action. 



(e) WATER a wearing and dissolving agent, also producing 

 chemical changes 2 (Figs. 2 and 3.) 



f Oxygen, 3 producing chemical change?, 



(/) GASES { Carbon dioxide, or carbonic acid gas, producing 

 [ chemical changes. 



2 Chemical changes are the decay processes in rock weathering. 



3 Oxygen is a gas composing 20.7 per cent of the air. Carbon dioxide is a 

 heavy gas consisting of the elements carbon and oxygen (CO 2 ). 



