Schuchert, C. “Climates of Geologic Time, In: The climatic factor as illustrated in arid America,” by Ellsworth Huntington. Washington, 1914, Pt. 2. CHAPTER III CONDITIONS BEFORE THE QUATERNARY ICE AGE The third of the great periods into which the geological record is divided is known as the Tertiary. Throughout most of its length it appears to have been characterized by remarkably mild and equable climatic conditions extending into comparatively high latitudes, so that the west coast of Greenland, for instance, had a flora of almost sub-tropical aspect. Since the plants in question—chiefly palms and cycads—are not of identical species with their present-day representatives, it is unsafe to base numerical estimates of the temperature upon them, but it is at least obvious that these regions were warmer than they are at present. Let us glance for a moment at the geography of the Tertiary period. The most noticeable point is a great expanse of sea over south-eastern Europe, including the Mediterranean countries, extending away over the Black Sea and Caspian, and stretching in a great arm to the Arctic Ocean, south of Novaya Zemlya. The geology of the archipelago north of Canada is not yet well known, but it seems probable that there was a considerable area of Tertiary ocean there also. The sea further encroached on the present boundaries of North America, both east and west, and on the north-eastern coast of Asia. Bearing in mind the principles set out in the first chapter, we can infer from these changes a great increase in the winter temperature of the regions along the Arctic circle. The increase reached a maximum on the west of Greenland and in western Siberia, but the west coast of Alaska also had a decidedly warm climate in the late Miocene and Pliocene. The basin of the Arctic Ocean, which already existed at that stage, was raised to a temperature considerably higher than the present by three great streams of warm water flowing into it. If, as seems probable, the Bering Strait was deeper, and the submarine ridge across the North Atlantic less pronounced, the obstacles to the outflow of cold water along the ocean floor were much less than now. Finally, the winter temperatures of the land-masses to the south, and especially Siberia, being already very much less severe owing to the sea over Europe, the temperature of the water of the great rivers flowing into the Arctic was not so low. For these reasons the development of ice in the Arctic Ocean was very much diminished, and possibly entirely absent, allowing a great amelioration of the climate of Greenland, the rigor of which is at present much enhanced by the ice which flows down the Greenland Sea and round Cape Farewell.