THE WORK OF STREAMS 



133 



the Hoang Ho in China. This river is restrained by great dikes 

 (p. 124), some of which are 30 feet above the level of the region ; but 

 notwithstanding these precautions many disastrous floods have 

 occurred. For several hundreds of years previous to 1852 this river 

 emptied into the Yellow Sea. In that year, when in unusual flood, 

 it broke through its north levees and emptied into the Gulf of Chihli, 

 some 300 miles farther north. This is only one of the many shiftings 

 which this river has made during its history (Fig. 112). During a 

 flood in 1887 many villages were destroyed, and the loss of life through 

 drowning and famine exceeded 1,200,000 people, more than the entire 

 population of Nebraska. 



Deposition in Lakes by Streams and by Other Agents 



Mechanical Deposits. — Streams deposit their loads when they 

 flow into lakes, forming deltas (p. 130) at their mouths and covering 

 the bottom of the lake with the finer silt, which is carried farther out 

 since it remains in suspension 

 longer. Lakes may in time be 

 entirely filled by the growth of 

 their deltas, first becoming 

 swamps and then level meadows 

 through which the streams may 

 flow in meandering courses (Fig. 

 123 A, B). Meadows of this 

 history are abundant in regions 

 which have been glaciated, such 

 as Michigan, New York, and 

 Minnesota. Lakes are shallowed 

 by the waves cutting back the 

 cliffs along their shores and carry- 

 ing out into them the material 

 thus derived. 



It is thus seen that as soon as 

 a lake comes into existence, 

 agencies arise which tend to 

 obliterate it; sediment begins 

 to fill it, and the outgoing stream 

 commences to deepen the outlet 

 and thus in time to drain it. 



Fig. 123. — Map A shows a lake being 

 filled in with sediment carried by streams. 



Map B shows the same lake converted 

 into a marsh, with the streams flowing in 

 meandering courses. 



