GLACIERS AND RIVERS COMPARED 219 



reaches the sea it is cut off, and its history of volume- 

 change ends abruptly. 



The velocity of flow is greater (7) in the middle of the 

 stream than at the sides, (8) at the top than at the bottom, 

 (9) on the outer side of a bend than on the inner, (10) 

 where the channel is narrow than where it is broad, (n) 

 where the grade is high than where it is low, (12) in a 

 large stream than in a small. 



(13) The surface of the stream, considered as to its 

 major features, is smoother than the channel bed. (14) 

 It is exceptionally high on the upstream side of an island, 

 and exceptionally low on the downstream side. (15) It 

 is roughened in detail by concealed prominences of the bot- 

 tom, especially where the stream is shallow. (16) The 

 surface descends normally in the direction of flow, but 

 exceptionally, and for short distances, ascends. 



(17) The stream erodes its bed and the walls of its 

 channel. (18) The chief tools of erosion are rock frag- 

 ments carried by the stream. (19) The greater the 

 velocity of the stream the more rapid the erosion (except, 

 perhaps, in cirques). (20) The stream shapes its chan- 

 nel, making the width several times greater than the 

 depth. (21) The fully adjusted channel is broader in 

 yielding material than in obdurate; but has uniform width 

 in uniform material. (22) The contours of the adjusted 

 channel are smooth curves of large radius. (23) The 

 adjusted channels of large streams are broader and deeper 

 than those of small streams. Where a large stream is 

 joined by a small tributary and the surfaces of the two 

 have the same level, the bed of the large stream lies lower 

 than that of the small. (24) The erosion of the channel in 

 gorges saps the cliff walls, causing coarse waste to fall to 

 the stream. (25) The waste from erosion and sapping is 

 carried forward by the stream and eventually deposited. 



(26) Where a heavily loaded stream issues from a moun- 



