Lakes Temporary Phenomena 



61 



pushed about by the ice floes of spring, and scattered 

 by every summer storm, but after every shift they set- 

 tle again at lower levels. Always they are advancing 

 and rilling the lake basin. The filling may seem slow 

 and insignificant on the shore of one of the Great Lakes 

 but its progress is obvious in a mill pond, and the dif- 

 ference is only relative. 



FIG. 12. An eroding bluff on the shore of Lake Michigan that is receding at 

 the rate of several feet each year. The broad shelving beach in the fore- 

 ground is sand, where the waves ordinarily play. Against the bare rising 

 boulder-strewn strip back of this, the waves beat in storms; at its summit 

 they gather the earth-slides from the bank above and carry them out into 

 the lake. The black strip at the rear of the sand is a line of insect drift, 

 deposited at the close of a midsummer storm by the turning of the wind on 

 shore. 



On the other hand, lakes disappear with the cutting 

 down of the rim of their basins in outflow channels. The 

 Niagara river, for example, is cutting through the lime- 



