The Quaternary, however, was not the only geological period to exhibit the phenomena of an Ice Age, and in order that we may more fully understand the status of the Quaternary Ice Age in the long succession of geological climates, and also to avoid the charge of presenting part of the evidence only, a brief discussion of the climates of the earlier periods has been attempted. The plan of the work is as follows: Chapter I deals generally with the causes of climatic fluctuations and with the meteorology of an Ice Age. Chapter II gives a brief account of the climatic record as a whole, and Chapter III deals with the Tertiary period considered as leading up to the Quaternary Ice Age. Chapter IV discusses the subdivisions of the Glacial period, and the conflict between advocates of one and of repeated glaciations. Chapters V to XII give brief accounts, _from the standpoint of a meteorologist_, of the glacial history of Northern Europe, the Mediterranean Region, Asia, North and South America, Africa, Australia, and the South Polar regions. In Chapters XIII to XV post-Glacial climatology is considered. Chapters XVI and XVII deal with the major climatic fluctuations of the “historic” period, and finally, in Chapters XVIII and XIX, is a short discussion of the influence of climate on the evolution and history of man. A brief bibliography concludes each chapter. THE EVOLUTION OF CLIMATE CHAPTER I FACTORS OF CLIMATE AND THE CAUSES OF CLIMATIC FLUCTUATIONS The climate of any point on the earth’s surface depends on a complex of factors, some of them due to influences arriving from outside the earth, and others purely terrestrial. Since any variations of climate must be due to a change in one or more of these, it is necessary, before we can discuss changes of climate, to consider briefly what the factors are. The only important extra-terrestrial factor of climate is the amount of radiant energy which reaches the borders of the earth’s atmosphere from the heavenly bodies—that is, from the sun, for the moon and stars can be ignored in this connexion. The only other conceivable factor is the arrival of meteorites, bringing kinetic energy which is converted into heat, and introducing cosmic dust into the atmosphere; but it is highly improbable that this is of appreciable effect. The amount of solar radiation[1] which reaches the earth depends in the first place on the total radiation emitted by the sun, and in the second place on the distance of the earth from the sun, both of which quantities are variable. It has been calculated that if other factors remained unchanged an increase of ten per cent. in the solar radiation would raise the mean temperature of the earth’s surface by about 7° C., or between 12° and 13° F., with, of course, a corresponding fall for a decrease.