484 JOHN LYON RICH 



which it would pass in its development ought to be matched in 

 actual valleys subjected to similar conditions. 



Rapid uplift of a meandering stream. — -Assume all initial con- 

 ditions the same as before except that the master stream instead 

 of flowing relatively straight, writhes in closely looped meanders 

 along its lower course toward the sea. Assume, as before, a rapid 

 uplift terminating after a moderate interval. 



Down-cutting, as before, will greatly exceed lateral cutting and 

 sweep and the stream will intrench itself with httle modification 

 into the bed-rock. On the sharper bends the accentuated lateral 

 cutting may succeed in producing under-cut bluffs and slip-off 

 slopes of moderate extent, but as a whole the stream will merely 

 intrench itself in its inherited course. The cross-section of the 

 valley, except at the sharpest bends, will approximate symmetry, 

 and the upland marking the original plain will extend unbroken into 

 the inside of the meander loops, in sharp contrast to the gently 

 decending slip-off slopes which mark the insides of the bends when 

 the meander has developed as uplift proceeds. 



As uplift and down-cutting continue, some of the narrowest 

 necks between meanders are likely to be cut oflf by under-cutting 

 as has happened at the Frying Pan Bend, and as may eventually 

 happen just above Handy's Bend in the Kentucky River (Fig. 2). 



Just so long, however, as the gradient of the stream remains so 

 great that down-cutting dominates, will the meanders continue 

 to intrench themselves deeper and deeper, still holding nearly 

 their original courses. 



When the uplift ceases, the master stream will quickly cut 

 down to grade. Thereafter deepening will be slow. Lateral cut- 

 ting combined with sweep will at once advance to the dominant 

 place, and the bottom of the valley will become widened. The 

 outside and down-valley sides of the meander bends will feel the 

 effects of the changed regime first and most strongly; flats will 

 develop; narrow necks like that at Handy's Bend (Fig. 2) will be 

 quickly cut through, making "rock islands" of the cut-off rem- 

 nants. Down-valley sweep will continue active and will tend to 

 remove, gradually, the spurs and rock islands from the valley and 

 to transform it into a flat-bottomed, crescent-bordered trough. In 



