[Illustration: +Fig.+ 168.—Shows the final change which resulted in the present course of the Tennessee. The land is represented as somewhat higher than now.[68]] 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 by the weakness of the strata over which they ran. At the same time, the uplift to the south led the southwesterly flowing stream (_b_, Fig. 167) to discover relatively hard beds of rock in its lower course, and these beds retarded its down-cutting. The result was that a tributary of the Ohio (_a_, Fig. 167) finally tapped the main stream flowing to the southwest (_b_, Fig. 167) and carried its upper part over to the Ohio (Fig. 168). This was the beginning of the present Tennessee. THE AGGRADATIONAL WORK OF RUNNING WATER. =Principles involved.=—Since deposition results from the failure of transportation, the factors which control transportation also influence 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.