RIVER PLAINS 401 



about half of the Province of Manitoba. A somewhat 

 similar plain is found in northern New York, bordering 

 Lake Ontario. This was formed at the time when the out- 

 let of the lake was the Mohawk River, the present outlet 

 then being obstructed by ice. The ice dam has since 



LAKE PLAIN. 



The ice dam in this lake has recently receded. 



melted, the lake has been lowered, and a part of its old bed 

 has been exposed. 



A change in the amount of rainfall may cause the for- 

 mation of a lake plain. If not as much water is furnished 

 to the lake as evaporates, the lake dries up and exposes 

 its bed as a flat plain with perhaps a small remnant of the 

 former lake still existing at the lowest part. Such is the 

 region around Great Salt Lake, Utah. 



185. River Plains. Sometimes a river widens its valley 

 enough so that it swings slowly from one side to the other, 

 and, at high water, floods the valley for a considerable 

 distance on either side of its course. A low, flat plain is 

 thus developed, sometimes terminating near the mouth of 

 the river in a delta. 



