THE CENTRAL BASIN OF TENNESSEE. 89- 



cannot at present estimate. The two more directly interested in the 

 work are rain and running water. These two had most to do with 

 formation of the basin of Tennessee. Ocean currents, it has been 

 gravely asserted, hollowed out the basin. Of the action of ocean cur- 

 rents we have no positive observations. Although they are very 

 powerful agents of transportation, there is a great probability that 

 they have no power as eroding agents. Ocean currents flow for the 

 most part of their course through water and having a bed of water 

 between the current and the bottom, thereby protecting it from any 

 coi-rading influence the current might have. Whatever planed off the 

 sub-carboniferous and other beds to the level of the Highland rim, or 

 hollowed out the basin, ocean currents had nothing to do with the 

 work. 



Tiansportation as we liave already stated is chiefly carried on by 

 running water. It is also carried on to a small extent by the aid of 

 the wind and atmospheric currents. The latter is more or less con- 

 fined to the sandy shores of the sea and arid sandy districts. 



Disintegration is carried on by weathering and slightly, in a 

 mechanical way, by running water. This action of running water 

 has been called corrasion. 



The chief agents in weathering are changes of temperature, rain as 

 a solvent and as a mechanical agent, gravity and vegetation. 



Sudden changes of temperature afiect material of every sort. Frost 

 following a saturated condition will by freezing fracture the hardest 

 rook wherever water has been enabled to penetrate. Softer rocks ai'e 

 disintegrated by the freezing and expansion of the water percolating 

 through their pores. 



Ruin is an agent of weathering in a two-fold capacity, the one as a 

 solvent and the other from a mechanical point of view. As a me- 

 chanical agent, the effects of rain are confined to the power of disin- 

 tegrating any loosely held or incoherent matter and detaching parti- 

 cles already loosened by frost. As an agent of solution, water is the 

 great solvent, not only inherently whereby many matters are dis- 

 solved, but also as an agent whereby various chemical solvents are 

 enabled to attack the different materials composing the rocks coming 

 under its power. While some rocks are disintegrated by complete 



