392 FIRST YEAR SCIENCE 



plains, and where high, especially if surrounded by steeply 

 descending sides, they are called plateaus. A good ex- 

 ample of the low, level area is the plain of northern Russia 

 and of the high area, the Arizona Plateau through which 

 flows the famous Colorado River. 



181. Coastal Plains. Experiment 130. Fill a tall glass jar 

 nearly full of water. Pour into this very slowly a mixture of sand 

 and finely pulverized clay. Note the effect upon the color of the 

 water. Allow the water to stand for several days and then examine 

 the deposition on the bottom of the jar. Are the sand and clay now 

 mixed as they were when poured into the jar? What effect has the 

 water had upon the mixture V 



We have already seen that the surface of the earth is 

 not stable, but is subject to movements. If the land bor- 

 dering a coast rises or the bottom of the ocean is depressed, 

 it causes the water to withdraw from the land, and a 

 strip of what was formerly sea bottom is changed into dry 

 land. 



This new area is composed of clays, sands and gravels, 

 often containing shells similar to those found on the 

 neighboring shores. The surface is comparatively flat, 

 but slightly irregular, and the drainage lines have not as 

 yet been established. The water that falls here which 

 neither evaporates nor sinks into the soil runs into the 

 slight depressions and makes shallow lakes. When these 

 become full, the water finds an outlet into a lower region 

 until at last it works its way to the sea. 



These outlet streams gradually establish themselves 

 and form a continuous line of streams and pools reaching 

 to the sea, with broad, poorly drained areas lying between. 

 The streams at once begin to cut down their beds and the 

 pools to fill up with the silt washed into them, -until at 

 last all the pools are drained and a network of streams 

 carries the run-off into the sea. 



