ACTION OF WATEE AND ICE 277 



overflow the banks and spread out over the plains on either hand. 

 But no sooner does the water leave the channel than the force 

 of the currents becomes checked, its carrying power lessened, 

 and it therefore begins to deposit its load of silt upon this flood 

 plain, as it is called, where it remains to permanently enrich the 

 land when the waters subside. It is to such processes of forma- 

 tion that are due some of the most fertile lands in existence, as 

 the valley of the Mississippi, that of the Eed Eiver of the North, 

 the Nile, and scores of others that might be mentioned readily 

 axxesti. 



To the same processes, coupled with the accumulation of 

 organic matter, we owe the filling in and gradual extinction of 

 thousands of glacial lakes throughout New England and the 

 North, and the formation of rich, flat-bottomed valleys known 

 locally as meadows, swales, and bogs. 



Ice in the form of glaciers is an efficient agent for transpor- 



■ till I 1 ^ I P ^MW| JiljL^ i y) ' v ' Ui i' iij. i I" I r f ' i."i" »t (S A^i if'j r^ » ■ ^ rr ^ 



■ I ' 1 I n I I l i i f i l- . | i " "^ i f j i i ^ & i hT . * ' i< '' ' "ijj ^ ^ y== s^''''T'' 3 1.1 .1 1 1 1 " I - _' ; I ' , ' 1... ' I' ' > ' I 1. "* 



Pig. 25. 



tation as well as for erosion, as already noted. While the work 

 being done by existing glaciers may seem comparatively insig- 

 nificant, that done by the ice sheet of the glacial epoch was by 

 no means so, and deserves a more than passing notice. The 

 manner in which the ice carries and deposits its load has already 

 received attention in speaking of its erosive power, and but 

 little more need be said on the subject. That material which 

 existed in a loose, unconsolidated condition, on the surfaces on 

 which the glacier formed, was pushed and dragged along by 



^ The Arkansas Eiver is stated by Owen (Geol. of Arkansas, 2d Bep., 1860, 

 p. 52) to be at certain seasons of tlie year almost blood-red from the quan- 

 tity of suspended fine ferruginous clay and saliferous silt brought down 

 from the regions of ferruginous shales, which prevail in the Cherokee County, 

 through which the river flows. This material, deposited along the banks and 

 in the eddies of still water, produces the celebrated red buckshot land. 

 Material washed from the bluffs of argillaceous shell marl, near the con- 

 fines of Jefferson and Pulaski counties, is deposited again farther down 

 the stream as a fine silt, imparting, like the red silt, extraordinary fertilizing 

 properties to the soil. 



