RIVER TERRACES AND REVERSED DRAINAGE 



671 



place, where by swinging it has undercut the valley wall. The 

 surface of the valley presents the aspect of a flat, level plain of 

 drift-filling from valley wall to valley wall, in which the Catatonk 

 River has excavated a shallow trench (Fig. 2). For the most 

 part this stratified drift in the valley bottom is composed of 

 rounded pebbles and coarse gravel, with intercalated beds of 

 sand and at some depth beds of clay. 



In the fall and spring the Catatonk River is rapidly converted 





Fig. I. 



into a flooded condition by the rains and melting snows decend- 

 ing rapidly from the high valley walls in a diversity of small 

 streams. Some of these latter are more or less persistent streams, 

 having a drainage heading back onto the plateau, or inter-valley 

 areas. They carry considerable detritus from the upland, and 

 plunge with a cascading rush down the escarpment of the main 

 valley to the master stream. Much of their sediment is often 

 deposited in alluvial fans, or cones, at the base of the valley wall, 

 where the equilibrium between volume and load is abruptly 

 broken. The residue, under a new adjustment, is strewn over the 

 valley flood-plain or delivered to the main stream. The main 

 stream is, therefore, for a part of the year essentially an aggrad- 



