. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 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 E
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 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-. â till I 1^ I P^MW|JiljL^iy)'v'Uii' I" I r f';i"»t (S A^iif'jr^ »â ^rr^ â I ' 1 I n I I li ifil-.|i" "^ifj ii^&ihT. * '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 brough
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