In present-day acceptance the term climate has come to be applied to the atmospheric conditions or weather normal to a given locality or region, especially as affecting life, health, comfort, and the multifarious activities of terrestrial existence. Although there are very considerable areas of the earth’s surface that exhibit similar climatic conditions, it needs little reflection to demonstrate that the climate of the earth is by no means uniform throughout. If, for instance, we travel either north or south from the equator, we pass successively through a so-called torrid zone, a temperate zone, and, in polar lands, a frigid zone, each with minor but distinctive modifications. In other words, the present distribution of climate is zonal.
This zonal distribution of climate on the earth, as we know it at the present time, is a phenomenon that appears to have had its origin, or at least its most marked accentuation, during . . .