THE CENTRAL BASIN OF TENNESSEE, 91 



power of corrasion. The moving power being the water of the stream 

 and the tools the fragments of mineral, mud or sand held in the water, 

 the more }'apidly these tools move the greater the amount of work per- 

 formed. This, of course, depends on the hai-dness, size and number of 

 the fragments in transition and also upon the hardness of the rock form- 

 ing the bottom of the stream. If the fragments be hard and the rock- 

 bedding soft the maximum amount of corrosion is i-eached. Although 

 the general tendency of corrasion is in a vertical direction, yet under 

 varying circumstances it works in a lateral direction, in which case 

 it forms a flood plain. " As an effect of momentum, the current is 

 always swiftest along the outside of a curve of the channel, and it is 

 there that the wearing is performed, while at the inner side of the 

 curve the current is so slow that part of the load is deposited. In 

 this way the width of the channel remains the same while its position 

 is shifted and every part of the valley which it has crossed in its 

 shiftings comes to be covered by a deposit which does not rise above 

 the highest level of the water. The surface of this deposit is hence 

 appropriately called the flood-plain of the stream. The deposit is of 

 neai'ly uniform depth, descending no lower than the bottom of the 

 water channel, and it rests upon a tolerably even surface of the rock 

 or other matei-ial which is corraded by the stream. The process of 

 carving away the rock so as to produce an even surface, and at the 

 same time covering it with an alluvial deposit is the process of jjlan- 

 ation." — (Gilbert, Land Sculpture, Geol. of Henry Mt. p. 121). 



In the course of the Cumberland River through the Central Basin 

 there are numerous poi-tions of the bottom of the basin along the 

 margins of the river that come under the denomination of flood plain. 

 The Signal Service have three river stations at which are recorded 

 the height and other particulars regarding the movements of the 

 watei'. At these are also given the flood plains in the various dis- 

 tricts. 



Station. Danger line feet. Area overflowed. 



Burnside, Ky 50 2.5 Sq. miles. 



Carthage, Tenn 40 90, " 



Nashville, Tenn 40 13. " 



In the neighbourhood of Nashville but outside of the immediate ai'ea 

 ■covered by the above 13 miles and lying within the great bends of 



