38 Adventures in Scenery 



the water will erode most where the soil is more soft, and so the 

 newly formed channel will tend to become crooked. A bend 

 in a stream means that the current will be more swift on the 

 outside of the curve, and so the bank in the bend of the channel 

 will be cut harder and the bend therefore be made greater. The 

 current striking the bend or curved side will be deflected over 

 to the opposite bank, and this bank further down-stream will 

 in turn be cut into, and so the crookedness of the stream will 

 be increased. Hence the winding courses of streams. 



If water fell uniformly over the new continent what be- 

 comes of the water that fell as rain farther from shore? All 

 it can do, and this is what does happen on flat lands, will be to 

 stand in sheets and shallow ponds if there are irregularities in 

 the surface until it is evaporated into the air or soaks into the 

 soil. 



How then does a river begin, and where does it begin? Evi- 

 dently it begins at its own mouth. How does it grow longer? 

 By pushing its head back landward. Does a river grow old? 

 Yes. It was young when it started. The first channel was a 

 V-shaped gully. The V-shaped valley grows longer by push- 

 ing back its head. It becomes crooked because of inequalities 

 in the soil. The stream valley is older down stream and 

 younger upstream. Every bend tends to widen the valley by 

 reason of cutting the bank and building up a bar on the inside 

 of the curve. Farther down the valley is more broad. Side 

 cutting of the banks tends to the development of a wider and 

 wider floodplain. A wide floodplain means that more sediment 

 is carried down from above than can be delivered at the mouth. 

 The river in its lower course has ceased to be down-cutting 

 and has become a building-up stream. It is building up its 

 bottom instead of digging it deeper. This is called aggrading. 

 Up stream it is degrading. Down stream it is older; up stream 

 it is younger. A river has grown old when its floodplain has 

 broadened till only low hills or ridges separate it from other 

 rivers on either side and the whole landscape has been reduced 



