The following study is an attempt to reconstruct in some detail the sequence of climatic changes through which the world passed during that important stage of its geological history which is variously known as the Ice Age or Glacial Period, the Pleistocene, the Quaternary, or the Human Period. That time saw the growth of humanity from a primitive stage but little removed from the higher animals to the beginnings of a complicated civilization, and it saw that human life spread from its cradle or cradles to the ends of the earth; it saw the configuration of the globe passing through a series of modifications which ended by establishing the physical geography of the present day. Finally, it saw a series of startling changes of climate which almost merit the term “Revolutions” of the old catastrophic geologists, at the conclusion of which we can trace the gradual development of the climatic conditions of the present day. In short, it is a period of immense interest which has a personal application lacking in the remoter parts of geological time, and for that reason it is worthy of the fullest study. On the geological side the literature of the Ice Age is immense, and is beyond the power of any one man to master. Volumes might be, and not infrequently have been, written on the glacial geology of areas limited to a few square miles, or even on the deposits of a single section. On the archæological side the literature is not yet so voluminous, but is technical and conflicting in a high degree. It is only when we seek the contributions of competent meteorologists that we find a serious gap in the literature. Nor is this surprising, for meteorologists are still so much occupied with the present vagaries of the weather, that few of them have time to extend their researches into the geological past. Yet this is eminently a case where the past is the key to the present, and it may be that the solution of many problems which meteorologists have hitherto faced in vain will yet be suggested by studies of the climatic changes of the Ice Age. The writer’s excuse for setting down his views is that he is intensely interested in all three sciences—geology, anthropology, and meteorology. The combination of these three subjects naturally ended in specialization on their common meeting place, and led him to hope that he could assist his fellow geologists and anthropologists by acquainting them with some of the bearings of meteorology on their subject, and could open out to his fellow meteorologists a fascinating branch of their science.