RIVER EROSION 155 
ured clay lands is weird and unique; and the surface 
is so irregular that it is almost impassable (Plate 4). 
On a rather extraordinary scale, this is an illustra- 
tion of what the rain is everywhere doing in a less 
noticeable way. Generally the rain action is less 
intense in its effect in moist countries; but even this 
picturesque action is not confined to dry regions, for 
on a small scale we may see it on nearly every clayey 
surface. In parts of Mississippi, the rains have so 
sculptured the clay lands of the abandoned plantations, 
from which the forest has been removed, that portions 
of the state resemble the true Bad Lands of the West. 
Supply of River Water.—A much more striking 
work of erosion is accomplished by the rain after it 
has gathered to form rivers. Passing off toward the 
sea, it gathers into streams, which carve channels for 
themselves. During a freshet or heavy rain, the river 
rises and becomes a torrent, and then perhaps sinks to 
a mere trickling stream, or even runs dry. 
If rivers depended entirely upon the direct gathering 
of the rain, they would become flooded during and im- 
mediately after each rain storm, and then would rapidly 
diminish until the next. But in fact, the river valley 
in most regions always holds water, particularly if the 
river is large. The reason for this is found in the con- 
stant supply from under ground, and from the litter of 
plant remains strewn over the forest floor. <A part of 
