DELTAS ' 189 



road as his means of communication with his neighbors, 

 are fine examples of submerged river systems. These 

 drowned river valleys enabled the early settlers to penetrate 

 easily into the country, and determined many of the early 

 settlements, like Philadelphia, New York, and Providence. 



Deltas. When a river enters a body of quiet water, 

 its current is gradually checked and it deposits its material 



LAKE BRIENZ FROM ABOVE INTERLAKEN, SWITZERLAND 



A rapidly eroding stream at the right has built a great delta dividing 

 the ancient lake into two parts. 



in somewhat the same way as on emerging upon a flat 

 country. But here the deposition is more gradual and 

 the slope of the deposited material less steep.- The sedi- 



