152 



PHYSICAL GEOLOGY 



and so the velocity, of the stream, which was then able to 

 cut a new valley in the floor of the old one. In its growth 



this young valley fol- 

 lowed up the old curves 

 of the river, and these 

 became intrenched me- 

 anders. 



Figure 142 shows a 

 young inner canon 

 formed in a wide older 

 valley in consequence of 

 uplift. After the river 

 had developed a wide 

 flat, the valley was so 

 elevated as to quicken 

 (rejuvenate} the stream, enabling it to cut the new, inner 

 valley. The broad remnants of the old valley flat constitute 

 terraces. River terraces may be defined as benches that 



FIG. 142. Sketch showing recent gorge 

 in older valley. Matanuska Valley, 

 Alaska. 



FIG. 143. Shoshone River at Cody, Wyoming. Shows Shoshone Canon 

 in the distance, with the south end of Rattlesnake Mountain on the right 

 and Cedar Mountain on the left, also the nearly level surfaces of portions 

 of the successive terraces. Irrigation is carried on extensively on the 

 terraces. (Fisher, U.S. Geol. Sum.) 



