490 



JOHN LYON RICH 



original level, what will be the consequences of a cessation of 

 uplift ? 



The stream, which as we have assumed has kept an approxi- 

 mately graded condition throughout the uphft, will soon cease 

 active down-cutting. Lateral cutting and sweep will, however, 

 continue. A flat flood-plain will begin to develop. All meanders 

 will be pushed down stream, some probably being cut off in the 

 process, leaving rock islands standing isolated on the flats. The 

 tell-tale slip-off slopes and undercut bluffs might, nevertheless, 

 remain in protected spots, and, at least until the new regime became 

 far advanced, would tell the story of the mode of development of 

 the valley, and, incidentally, of the slow and continuous character 

 of the down-cutting. Should the land remain long enough at one 

 level all traces of the undercut bluffs and shp-off slopes would 

 finally be obKterated, and the stream would swing in its meanders 

 across a flat, open flood plain bordered by meander-scalloped 

 valley walls, or bluffs. 



Thus we see that the end product in this case is similar to that 

 in the others and that the distinctive valley types are characteristic 

 only of the youthful and mature stages of development, while all 

 tend to become alike in the old age stage. 



Slow uplift of a meandering stream. — ^If, with initial conditions 

 as in the last case, we assume, instead of a straight stream, a 

 meandering one with uphft slow enough to keep the master stream 

 cutting down, but never to its full capacity, we should expect 

 lateral cutting, as before, to play a relatively important part from 

 the first. The original meanders would increase in width as they 

 intrenched themselves into the rock. Cut-off's would probably 

 occur. The form of the valley would be that of the in-grown 

 meander valley with undercut bluffs on the outsides of the 

 meander bends, or concave banks, and slip-off slopes on the 

 insides or convex banks. There would probably, however, be 

 some of the features of the intrenched meander such as the flat 

 upland between the original meander bends. In the earher stages 

 of the development of such a valley it might be possible to 

 determine definitely whether the original stream was meander- 

 ing before the uphft by noting whether or not slip-off slopes 



