It is not disputed that there was a very considerable upheaval of the land, especially in Europe and North America, at the end of the Tertiary Era. Every mountain chain advanced, and our Alps, Pyrenees, Himalaya, etc., attained, for the first time, their present, or an even greater elevation. The most critical geologists admit that Europe, as a whole, rose 4000 feet above its earlier level. Such an elevation would be bound to involve a great lowering of the temperature. The geniality of the Oligocene period was due, like that of the earlier warm periods, to the low-lying land and very extensive water-surface. These conditions were revolutionised before the end of the Tertiary. Great mountains towered into the snow-line, and vast areas were elevated which had formerly been sea or swamp. This rise of the land involved a great decrease in the proportion of moisture in the atmosphere. The sea surface was enormously lessened, and the mountains would now condense the moisture into snow or cloud to a vastly greater extent than had ever been known before There would also be a more active circulation of the atmosphere, the moist warm winds rushing upward towards the colder elevations and parting with their vapour. As the proportion of moisture in the atmosphere lessened the surface-heat would escape more freely into space, the general temperature would fall, and the evaporation--or production of moisture would be checked, while the condensation would continue. The prolonging of such conditions during a geological period can be understood to have caused the accumulation of fields of snow and ice in the higher regions. It seems further probable that these conditions would lead to a very considerable formation of fog and cloud, and under this protecting canopy the glaciers would creep further down toward the plains.