THERE is undoubted evidence thaat at some period or periods in the earth's history the climate in polar regions was much less severe than it is at present. In the Arctic there are indications of a climate when vegetation similar to that which is now found in subtropical regions flourished in Greenland and Spitsbergen. Geologists have generally supposed that during these periods the temperature over the whole earth was much more uniform than at present, so that the temperature difference between the equator and the poles was very small, if it existed at all. These conditions are explained as the consequence of vast oceanic currents carrying warm water to polar regions. The Gulf Stream Drift now maintains a mean annual temperature off the coast of Norway in latitude 70° N., which is 10° C. higher than the mean temperature of the latitude, and it is supposed that if its volume, velocity, or both were increased, and other streams introduced, even higher temperatures could be maintained over the whole of the north polar regions. This supposition is based on an entirely wrong conception of the physical causes which maintain the existing climatic zones.