This is the probable reason why a line of glacial débris, largely composed of bowlders, is found to extend across the Middle and Western States, and so generally supposed to be the glacial boundary of a frigid period. But there is no reason to suppose that an ice-sheet, although deprived of its eroding power, was arrested in its southern movement on the line of its stony débris, because there could be no sudden change of temperature in a particular latitude on the eastern lands of North America to cause an abrupt ending of the ice-sheets. And there appears to be nothing to hinder the ice from gathering and flowing over lands warm enough to loosen its implements of erosion; for there is much to show that the ice-sheets flowed much further southward, even into the middle portion of the Gulf States, and there spread the clay mixed with gravel and pebbles, with now and then a bowlder, over the land. The scattered bowlders, found in numerous instances many miles south of the bowlder line, were so deeply imbedded in the ice-sheet that they could not be dropped on the usual releasing ground. The ice-sheet, when deprived of its rocky, eroding implements, would, while flowing over the land, leave few or no imprints on the rocks; but it would probably move and spread a large amount of clay, gravel, pebbles, and sand over its wide course, especially if the ice moved from a region abounding with such material. Should we place the glacial boundary on the line of the rocky débris, how could we account for the glaciated stones found on the hills and plains situated far southward of the bowlder-strewn regions of the Middle and Western States? The clay mixed with gravel and sand, and spread so broadcast over a large portion of Georgia and even into Northern Florida, makes it appear that the ice of a cold period must have covered that southern region. Moreover, it seems to have been through the great abrasion which only ice-sheets could perform that the sands of the Florida peninsula were produced; for on examination they seem to have resulted from the abrasion and weathering of crystalline rocks.