Page:Popular Science Monthly Volume 68.djvu/315

Rh Hudsons Bay and the polar seas, which, floating over the northern part of the United States, would be met by the warm waters of the Gulf Stream, causing them to deposit their loads. The warm current flowing northward would be superimposed on the cold current, the latter continuing southward beneath it, transporting the finer materials, such as now occupy the lower Mississippi Valley.

Emmons likewise believed the agent of drift transportation to be water and ice. The boulders he thought to be the work of icebergs, but the striations and polishing he felt could not be due to this agency, since the bottom of the ocean is not bare rock, but covered by debris, and, moreover, icebergs would not move in straight lines, a point which some more recent writers have quite overlooked. The bergs might act as agents of transportation, he argued, but not of erosion. According to his ideas the drift-covered region was, during the drift period, depressed, the country low and connected at the north with an extensive region giving rise to large rivers which flowed in succession over different parts of the region lying between Champlain and the St. Lawrence. These rivers united with the Atlantic on the south through the Champlain, Hudson and Mohawk valleys. They bore along ice loaded with sand, pebbles, etc., which scratched and grooved the surface of rocks over which they flowed, and were the agents also of perforating the rocks in the form of pot holes.

Hall's ideas were somewhat hazy. That he did not accept Agassiz's doctrine of a vast ice sheet is very evident. Thus, he wrote that

Blocks of granite, either enclosed in ice or moved by other means, have been the principal agents effecting the diluvial phenomena; that they have scored and grooved the rocks in their passage and, breaking up the strata and mingling themselves with the mass, have been drifted onward carrying everything before them in one general melee. That such may have been the case in some instances or in limited localities, can not be denied; but that it ever has been over any great extent of country will scarcely admit of proof.

Hall was at this time evidently a catastrophist and regarded the drift soils, terraces, and the deep valleys and water courses as due to the violent action of water which may have been caused in part by a sudden submergence and the rapid passage of a wave over its surface. His views, indeed, were in many respects little, if any, in advance of those held by Mitchill twenty-five years earlier. Like Mitchill, he conceived of an inland sea bounded and held back by the Canadian highlands on the north, the New England range on the east, and highlands of New York and the Alleghenies on the south, and the Rocky Mountains on the west. These presented barriers of from one thousand to twelve hundred feet above the level of the ocean until broken through by the St. Lawrence, the Susquehanna, the Hudson, partially by the Mohawk at Little Falls, and perhaps also by the Connecticut.