PAET III. WORK AND ENERGY 



CHAPTER XV 

 WORK BY RUNNING WATER 



183. The power of running water. Those who bathe in the 

 surf of the ocean or of large lakes soon come to have an appre- 

 ciation of the power of moving water. The power of the waves 

 is even more impressively shown by the damaged piers, ruined 

 breakwaters, and wrecked vessels which sometimes strew the 

 coasts after severe storms. 



The power of flowing water may be felt as one wades a small 

 creek; its possible magnitude is exhibited only too often by 

 the results of floods and freshets. Even small streams may, in 

 flood times, destroy bridges and roads, tear down stone walls, 

 carry away buildings, and wash the fertile soil from great 

 areas of land. 



184. Work done by Niagara Falls. One of the most impres- 

 sive examples of the power of running water is to be found in 

 the falls and gorge of the Niagara River. This river flows from 

 Lake Erie to Lake Ontario. Several miles from Lake Erie the 

 water falls about 160 feet into the head of a narrow gorge, 

 through which it races swiftly toward Lake Ontario (fig. 83). 

 The falling water has worn a deep pool and has also undermined 

 the foot of the cliff over which the water falls. From time to 

 time masses of rock at the edge of the cliff are loosened by 

 undermining and fall into the whirling pool below. In this way 

 the face of the cliff is slowly eaten away and recedes upstream. 

 The falls are moving upstream toward Lake Erie at the rate 

 of about 5 feet per year, lengthening the gorge by that amount. 



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