The Coming Ice Age

by C. A. M. Taber

An account of a collecting expedition to Lower California by G. Eison, in 1895, describes ancient moraines at the extremity of the peninsula as being prominent, large, and steep. This region lies under the tropic of Cancer, and 8° south of the mouth of the Colorado River where it empties into the Gulf of California. Hence it appears that the temperature of that portion of North America during the ice age was favorable for the great glacier of the Colorado Canyon to have flowed into the Gulf of California.

The wide, shallow basins of Utah and Nevada were filled with the water from the melting ice-sheet on the breaking up of the ice period, and the lakes so caused remained for a considerable time after the disappearance of the ice. But, owing to the great evaporation and light rain-fall of that region, the lakes gradually shrank away, the filling and emptying of the lake basins being governed by the cold and mild epochs.

The conglomerate deposits in the Appalachian district of North America are known as occurring on a large scale. Professor Shaler is inclined to attribute them to glacial action, because he knows of no other force that could bring together such masses of pebbles from a wide-spread surface. In Eastern Kentucky and East Tennessee these deposits are found to be several hundred feet in thickness. Such accumulations of apparent glacial origin are to be found from New Brunswick to Alabama.

Hence it seems that the ice during a frigid period followed down the Alleghany range even so far south as Georgia and Alabama; and for a time, when the ice attained its greatest spread, it flowed over the central portion of the Gulf States. For how else can we account for the clay mixed with gravel and pebbles and stony fragments being spread broadcast over that region?

I know that such statements do not agree with the views of glacialists who have written on the subject, and have drawn the glacial boundary from seven to ten degrees further north, where a line of bowlders with other glacial débris is plainly traced. Still, it appears to me that a line of bowlders deposited by an ice-sheet spreading over a continent and across many degrees of latitude cannot be compared to the moraines of inferior mountain glaciers of the temperate latitudes of the present age.

An ice-sheet moving from a high latitude to a lower would, while in the colder latitude, freeze firmly to the rocky ledges, and hold them so strong in its frigid grasp as to break off the weaker portions of the rocks, and drag them toward a milder region, as far as the freezing grip of the ice-sheet would permit; but, on gaining lower and milder latitudes, the holding and dragging power of the ice would be lost on account of the increased warmth of the earth over which the glacier must pass, and also because of the ice-sheet having lost a portion of the low temperature acquired in the higher latitudes. Therefore, on such lines the bowlders would be released, while the ice-sheet would still move on, although largely deprived of its eroding power.

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.

The worn remnants of such rocks are now found in the southern Appalachian range. In fact, the hills and mountains of that region at the present time are supposed to be a small remnant of the ancient highlands. Thus, on consideration, it appears that the sands caused by the action of glaciers were, on the disappearance of ice-sheets, blown by the strong north-west winds toward the Florida peninsula as fast as the receding waters of the ocean which flowed the lowlands on the breaking up of the ice age would permit; and in this way the sand was spread over the lowland region, which was largely composed of coral sea shells and other marine matter. And it seems that the sand must have been blown over large areas in Florida soon after the ending of the frigid period, because the sand, in order to be moved by the winds, must have spread over a country nearly destitute of vegetation; and such would be the condition of that region during times which succeeded the ice period and the subsequent brief flowage of the lowlands on the ending of the frigid age, which would not be the case if such sands resulted entirely from water erosion and weathering, because with such a state of things the country would be covered with forests and grasses, which would prevent the sand from being moved by the winds to any great extent.