UNIT IX 

 ROCKS AND SOIL 



PREVIEW 



How many of you have ever been to the top of a high 

 mountain ? You remember how it looked a great 

 mass of solid rock with perhaps a few trees clinging here 

 and there in places where there was a little soil. If you 

 worked your way down the mountainside, you would 

 probably follow the course of a tiny brook which, as you 

 descended, you would notice had cut its way deeper and 

 deeper between rocky walls and slopes of broken particles 

 of rock. Look at those rocks carefully. They all seem 

 to be angular bits, not rounded like the pebbles you find 

 in the valley at the foot of the mountain or on the beach. 

 The rocks on the mountainside look as though they might 

 have been cracked off and broken up by some force, 

 perhaps great heat or cold. Let us scramble down a lit- 

 tle lower. Trees, shrubs, and plants begin to be more 

 numerous, the rocks are giving place to soil, some of it 

 black and rich. You find more inhabitants of the forest 

 - birds, squirrels, and other small animals. If you dig 

 in the ground, you may find earthworms, beetle larvae, 

 and other living things. The brook is inhabited, too : 

 insect larvae in the water, flies and mosquitoes hovering 

 over its surface, and perhaps small fish, even trout, lurking 

 in its pools. And now the rocks and pebbles over which 

 the brook rushes show the familiar rounded look of those 

 stones which we know were polished by the action of 

 water. At the foot of the mountain we may find the 



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