And it seems that this arrangement for bringing about a frigid age made slower progress in its early stage than at this date, owing to there having been a lack of glacial ice in the polar regions to produce icebergs for cooling the ocean waters. But the independent circulation of the great southern ocean, after turning away the tropical currents from the high southern latitudes for thousands of years, did at length cause glaciers to form on the antarctic lands, which have been slowly, but constantly increasing; and, consequently, the cooling of the ocean has been accelerated proportionate to the increase of ice-sheets. Therefore, with the cooling process so well advanced as it now appears to be, it seems that more than half of the time required to bring a frigid age to perfection has been expended since ice-sheets began to gather on the antarctic shores. For, when we realise how the facilities for making ice have advanced through the increase of glaciers in both hemispheres, and how large a portion of the ocean waters have been cooled below a temperate or tropical temperature even in the torrid latitudes where the warm upper waters of the ocean have been reduced to a comparatively thin stratum when compared to the vast bulk of the cooled under-waters, it appears that the cold will increase at a faster rate for the next thousand years than was the case during the last ten centuries. Therefore, the climate will be less favorable for plants and animals existing on lands in the high latitudes for the next thousand years than during the ten centuries preceding; and, when we take into consideration the accelerative growth of a frigid epoch, it seems that the increasing cold will in a few thousand years drive the greater portion of both plants and animals from the now temperate latitudes to maintain an existence in the tropical zone, where a large part of the existing species of such life must have taken refuge during the last ice period.
And, from what can be learned from the relics of man’s prehistoric life, it seems to point to the lands of the tropical latitudes as having been his home during the frigid ages; and, because of his long undisturbed residence in favored portions of the tropics, he there attained his earliest civilization. For it appears that the tropical zone was not only less burdened with ice in glacial times than the higher latitudes of the globe, but was also more exempt from the great flooding of lands which obtained in the more northern latitudes through the shifting of the ocean waters, from causes set forth in the preceding pages. Yet it may be said that the low lands of the tropical zone south of the equator during cold epochs were much more extensive than at this age, on account of the shrinkage of the sea, because of the great amount of water evaporated from its surface, and stored in ice-sheets on the great continents and islands. Hence the reefs and shallows which surround such tropical islands as include the Seychelles Archipelago, and also the extensive banks covered with shoal water in that portion of the Indian Ocean, were during the glacial period elevated above the surface of the sea, possessing a climate favorable for vegetable and animal life. But, owing to the great rain-fall of that region, it is probable that the highest lands were glaciated, as it is reported that granite bowlders still rest on the mountain slopes of the highest island. The numerous islands and shoals of the south-western tropical Pacific must also have afforded wide land areas, with a temperate climate, owing to their having been situated on one of the warmest regions of the earth during the ice age.
Moreover, it is probable that these tropical lands afforded space for numerous lagoons which had little connection with the surrounding oceans, and consequently were able to maintain, in their secluded shallow basins, a warmer temperature than obtained in the open seas; and at the same time, owing to the great rainfall in such tropical portions of the Indian and Pacific regions, the waters of the lagoons were rendered less salt than the briny depths of the shrunken oceans of a cold period. Hence because of such conditions the fauna of the tropical seas were preserved from the destructive rigor which beset the earth during the frigid epochs.
Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a predominant preference was found in the original book; otherwise they were not changed.
Simple typographical errors were corrected; unbalanced quotation marks were remedied when the change was obvious, and otherwise left unbalanced.