THE WORK OF RUNNING WATER, 177 



the region had been considerably extended by the withdrawal of the 

 sea, the Appalachian River itself was reached by the invading stream, 

 and its waters carried away to the Mississippi Ba}^ by a course the 

 lower part of which is thought to have corresponded approximately 

 with the course of the present Black River {h, Fig. 167). 



Still later there was further deformation which caused additional 

 changes in the drainage. The whole region was uplifted, relatively if 

 not absolutely, but the uplift was differential, being greatest along the 

 axis represented by AB, Fig. 167. The effect of the deformation was 

 to stimulate the tributaries of the Ohio flowing north from this axis. 

 Their growth was further accelerated b}^ the weakness of the strata 

 over which they ran. At the same time, the uplift to the south led the 

 southwesterly flowing stream (6, Fig. 167) to discover relatively hard 

 beds of rock in its lower course, and these beds retarded its down-cut- 

 ting. The result was that a tributary of the Ohio (a. Fig. 167) finally 

 tapped the main stream flowing to the southwest (6, Fig. 167) and car- 

 ried its upper part over to the Ohio (Fig. 168). This was the begiiining 

 of the present Tennessee. 



THE AGGRADATTONAL WORK OF RUNNING WATER. 



Principles involved. — Since deposition results from the failure 

 of transportation, the factors which control transportation also in- 

 fluence deposition. Transportation by streams is determined largely 

 by velocity, and the most important factors influencing velocity are 

 slope, volume, and load (p. 115). Of these the first two are usually 

 of greater importance than the third. 



A stream is said to be loaded when it has all the sediment it can 

 carry; it is loaded with fine material when it has all the fine material 

 it can carry, and with coarse material when it has all the coarse it 

 can transport. A stream loaded with coarse material flows more 

 swiftly than one loaded with fine, for a larger percentage of a stream's 

 energy can be utilized in carrying fine material than coarse, and hence 

 a larger percentage of the energy of a stream which carries a load of 

 the latter will express itself in velocity. 



Deposition takes place whenever a stream finds itself with more 

 load than it can carry^ and is an expression of the stream's refusal 



