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ROCKS AND SOIL 



In one of the Indiana marble quarries we found splendid shells of 

 water animals and the skeleton of a fish. You doubtless remember 

 that marble is a metamorphic variety of limestone and so shows 

 the same fossils that limestone would. 



PROBLEM III. HOW IS SOIL MADE? 



Soil Is Rock. From what we have learned, we can 

 see that soil is formed from rock. There are many 

 agents at work, and this work is going on right under our 

 eyes. Take a rocky ledge such as is shown in the cut. 

 Beneath this ledge is a slope of broken pieces of rock, 

 some of which are small enough to make a coarse soil. 

 The rock breaks down to form this slope of fragments, 

 called a talus. But what causes it to do this ? Evidently 

 the forces of air, heat, cold, water, and gravity are at 

 work. Any changes in rocks brought about by changes 



in weather or the 

 atmosphere are 

 called weathering. 



Mechanical 

 Weathering. Some 

 rocks are broken by 

 the action of frost 

 and the sun's heat. 

 We know that frozen 

 water occupies al- 

 most 10 per cent 

 more space than in 

 a liquid state. Try 

 the experiment of 

 freezing a corked 

 bottle full of water 

 and see what hap- 

 pens. When water 

 inclosed in a crack 



What kind of rock is shown here ? Find the talus 

 slope. How would you say rocks form soil ? 



