From time to time I have been given an opportunity to discuss in the Geological Magazine the question of the cause or causes of climatic variations. The subject is one of deep interest to the geologist. Even Lyell, in the first edition of his Principles of Geology, gave a good deal of space to it, but contented himself with merely pointing out that variations in the distribution of the land would lead to changes in the climate. He wisely limited himself to this aspect of the question, for, at that time, the directions of the winds in middle latitudes were not such as meteorological theory would have led us to expect.