Ice-Ages

Abstract

The earth’s aspect is a very recent one from a geological point of view. Everyone knows that Greenland and Antarctica are at present covered by extensive ice-caps (fig. 71). Yet only one tick back on the geological clock large parts of America and Europe were covered by analogous ice-sheets of enormous dimensions. In Europe the ice-front extended from the British Isles to the Netherlands, and from there to Germany and North Russia, covering the whole of Scandinavia. Another ice-sheet covered the Great Lakes district of North-America and practically the whole of Canada (fig. 72). Indisputable traces of large glaciations in South-Africa, South-America, Australia and a few other regions date from a still more distant past — the Upper-Paleozoic (fig. 73), or even remoter times — the Precambrian, when plant-life had not yet imposed itself upon the land, and the seas were only populated by Invertebrates (fig. 74). Rocks whose origin cannot be explained unless we assume that they were formed under the same conditions of heat and drought as are now found in the Sahara (fig. 79) are met with in many places in Europe and America. On the other hand, the fossil remains of a luxuriant vegetation are still observed in such bitterly cold regions as Spitsbergen and Greenland.

“We are apt to think that our present conditions are normal, but that is far from being the case”.

(A. P. Coleman).