This goes to show that the region of the Gulf States was so much affected by the cold of the glacial period, together with the submergence of the lowlands at its close, its flora and also its animals were exterminated; for how else can we account for the abundant fossil remains of animals now found buried in the Florida sands? It appears also that, when Florida was being covered with drifting sands, many of the lake basins now formed did not exist, as the wind-blown sand could not have crossed a continuous chain of lakes like the St. John’s River; and it is an easy matter to-day to trace the beds of the ancient lakes that prevented the sands from drifting over certain lands now nearly destitute of it. And it is probable that the sea flowed the lowest lands during the period when the winds were drifting the greater portion of the sands over the peninsula. Therefore, regions which embrace the Everglades and portions of the Indian River territory are quite free from heavy sand deposits, and so also are the extensive flat woods of the peninsula.
Since the sands blew over the ancient desert of Florida, many lake basins have been formed because of the sinking of the ground. This sinking of the ground is a common occurrence in limestone regions, where a great amount of material is moved in solution, leaving caverns whose roofs often fall in. The great amount of sand blown upon Florida caused the marine strata to give way in the weaker places under its burden. The sinks thus formed, probably of frequent occurrence at one time, have now nearly ceased. Still, there are depressions to be seen to-day where the tops of large pine-trees, which grew on dry, sandy land, are barely above the surface of the water which partly fills the basins so recently formed. Yet I would not assert that all of the depressions where Florida lakes exist were caused by the sinking of the ground; for the winds may have caused shallow basins in the sand, where the decayed vegetation has formed mud sufficient to hold the water which now partly fills such basins.
The mobility of Florida sands can be seen to good advantage when exposed to a strong, dry north-west wind, where the ground happens to be destitute of vegetation. An observer can then realize what the result would be, should the whole land be deprived of vegetation and laid bare to the action of the winds.
Under such conditions, not only would the winds be much stronger than now, but the air near the ground would be filled with sand, moving like drifting snow in a Dakota blizzard. And, furthermore, it is probable that the rainfall was very light while Florida was void of vegetation; and, even if shallow basins were formed, there would be a lack of rain to supply them with water.
The wide plains west of the Mississippi River, extending southward into Texas, during the frigid period must have been covered with a sheet of ice and snow. And it is probable that it was not wholly a product of more northern latitudes, but was mostly produced by the snow which fell on the plains during the long winters of that period, which could not be melted away during the cold summers of an ice age, when it is considered that an ice-sheet, with a temperature sufficiently low as to carry glacial drift, covered the lands of Missouri as far as latitude 38° south; and it may have been through the pressure from an ice-sheet in its south-eastern movement that we are to account for the numerous ore-bearing faulting fissures traversing the limestone strata.
The ice-sheet was also the probable cause of the erosion of the horizontal bedded stones, yet it appears that the ice did not greatly change the contour of the ground; for it is well known that glaciers do move over lands that are not frozen to the ice without causing much disturbance, especially where the gradient is small, and this was the probable condition of the Western plains during the ice age. Thus it seems that whatever disturbance this region has undergone could be partly attributed to ice-sheets without the presence of bowlder drift, because the temperature and texture of the ground in the limestone region were unfavorable for such accumulations; yet it may be owing to the action of ice that minerals once diffused are now found collected in fissures. The deep valleys through which the large rivers now pass on their way toward the sea were once filled with glaciers which flowed into them from their tributaries. Thus the deep trenches of the plains are largely the work of glaciers. It is generally supposed that the driftless region of Wisconsin was free from ice during the frigid period. But it seems impossible for this region to have escaped being covered by ice and snow, with the great lakes filled with glaciers, and the regions on all sides of the driftless area covered with ice.
The reason why this territory escaped the drift from the north was on account of the hindrance which the drift-bearing ice-sheet encountered in the deep basin of Lake Superior. In this great depression the ice-sheet from the north was relieved of bowlders and other glacial drift, as well as obstructed in its southern movement.
Therefore, the snow and ice which gathered on the driftless region had little movement in any direction, while the temperature and consistency of the ground under the ice were not favorable for the production of bowlder drift; and, when we consider that the Mississippi valley was deprived of great sources of warmth during the culmination of a glacial period, we are forced to the conclusion that its wide lands were also covered with snow and ice.
The tropical waters of the North Atlantic were so much chilled by the floating icebergs of North-eastern America, Greenland, Iceland, and Northern Europe that the Caribbean Sea, its warmest reservoir, was reduced to a temperature so low that the easterly winds which blew over its waters were unable to prevent ice-sheets from gathering on Eastern Nicaragua.
Therefore, during such frigid times it appears that, with the waters of the Caribbean Sea and Gulf of Mexico reduced to a low temperature, it was impossible for the great Mississippi valley to escape glaciation, while being surrounded by cold seas and glaciated lands which extended even into the tropical latitudes. The broad, level lands of British America and Siberia during the ice age must have been thickly covered by the snow which fell on the deeply frozen plains, besides the large amount of snow that the cold westerly winds must have drifted over their icy surface from lands of greater snow-fall on their western borders. This snow during such freezing times could not be melted away.