474 JOHN LYON RICH 



It is especially characteristic of this type that the portion of 

 the upland between the meander loops keeps its full height and 

 fiat surface almost to the inside end of the loops. The valley, in 

 cross-section through the end of one of the loops in a direction 

 transverse to the general direction of the stream, is practically 

 symmetrical. There is a slight tendency to the development of 

 "slip-off slopes" and undercut bluffs, but it is subordinate. 



3. The in-grown meander valley is well shown on many of the 

 United States topographic maps. One of the most beautiful which 

 has come to my notice is portrayed on the southern part of the 

 Lockport (Ky.) sheet, where the valleys of the Kentucky River 

 and Elkhorn Creek display with great clearness the characteristics 

 of the type (Fig. 3). The concave and the down- valley banks are 

 marked by steep bluffs, while on the insides of the loops are well- 

 marked sHp-off slopes descending gently to the river. This 

 characteristic feature is clearly shown on the inside of the loop just 

 above Johnson Ferry (X on the map, Fig. 3). 



Such a valley presents clear evidence that whatever may have 

 been the course of the river in a previous cycle, the meanders have 

 been much widened and enlarged during the present cycle. 



All three of the valleys described above are the products of com- 

 paratively young and decidedly vigorous streams. All three, 

 moreover, are in approximately the same stage of development in 

 the erosion cycle — namely, youth to maturity. All are, or have 

 recently been, degrading streams. We cannot, therefore, ascribe 

 the differences in valley form to differences in the stage of develop- 

 ment of the valleys. The differences are more fundamental than 

 that. Nor are we deahng with old-age streams in which the 

 meanders are features of the flood plain. Such old-age streams and 

 valleys may be looked upon as end products of the development of 

 any one of the types of valley described above. 



Having recognized these distinctive valley types we are con- 

 fronted with the problem: What conditions determine the type of 

 valley which a stream will develop ? A satisfactory solution of 

 that problem calls for a brief review of some of the basic principles 

 of river work. 



