It should be borne in mind that at all times a glacier is accompanied by the issue of vast streams of water from its front, and that these of course increase in volume when the climax has been reached and the ameliorating influences begin to melt away the accumulated mass of ice and to add the volume of its water to that produced by ordinary agencies. As these subglacial streams of water poured out upon the more gentle slopes of the area in front of the ice, they would distribute a vast amount of fine material, which would settle into the hollow places and tend to obscure the irregularities of the previous direct glacial deposit. Such an instance came clearly under my own observation in the vicinity of Yankton, in South Dakota, where, upon visiting a locality some miles from any river, and to which workmen were resorting for sand, I found that the deposit occupied a kettle-hole, filling it to its brim, and had evidently been superimposed by a temporary stream of water flowing over the region while the ice was still in partial occupation of it. Thus, no doubt, in many cases, the original irregularities of the direct glacial deposits have been obliterated, even where there has been no general subsidence. But, in the area under consideration, the loess, or loam, is so extensive that it is perhaps necessary to suppose that the central portions of the Mississippi Valley were subjected to a subsidence amounting to about five hundred feet; so that the glacial streams from the retreating ice-front met the waters of the ocean in southern Illinois and Indiana; thus accounting for the extensive fine silt which has done so much over that region to obscure the glacial phenomena. _West of the Rocky Mountains._ The glacial phenomena in the United States west of the Rocky Mountains must be treated separately, since American geologists have ceased to speak of an all-pervading ice-cap extending from the north pole. But, as already said, the glaciation of North America has proceeded from two definite centres of ice-accumulation, one of which we have been considering in the pages immediately preceding. The great centre of glacial dispersion east of the Rocky Mountains is the region south of Hudson Bay, and the vast ice-field spreading out from that centre is appropriately named the Laurentide Glacier. The movement of ice in this glacial system was outward in all directions from the Laurentian hills, and extended west several hundred miles, well on towards the eastern foot of the Rocky Mountains.