Before the Glacial epoch, in particular, the discovery of the year, organically or consciously, must have been much more difficult than it is now in high latitudes. It must have been almost as difficult in what are now the temperate zones as it is to-day in the tropics. Far north or south, of course, the length of the day would tell; and within the Arctic and Antarctic Circles the long night would form an unmistakable feature. But if the plane of the equator had always found itself vertical to the sun, there could have been no recognition of the year at all, either organic or conscious. In other words, from the point of view of organic life, the year does not mean the revolution of the earth round the sun: it means the apparent northward and southward movement of the sun on either side of the equator; it means the seasons, whether recognized as winter and summer, or as dry and wet periods. That is really the year as man knows it, as plants and animals have always known it. With the coming on of the great cold spell, however, the importance of the seasons in the temperate and frigid zones, perhaps also even in the tropics, became much more marked. I will not go here into the suggested reasons for that vast revolution, perhaps the greatest our planet has ever suffered. Most physicists now accept more or less the theory put forward with great ingenuity by Mr. Croll, which sets it down to a period of extreme eccentricity in the earth's orbit; but some weight must also be allowed, as Mr. Alfred Russel Wallace has clearly shown, to the local arrangement of land and water on the globe at the time of its origin, as well as to the occurrence of mountain ranges just then at the poles, and to other purely terrestrial causes. Never before, in all probability, had the poles been occupied by great glacier-clad mountains. It seems most likely, indeed, that we are now practically at the end of the Glacial epoch, and that if only we could once get rid of the polar ice caps, which keep a stock of chilliness always laid on (I speak the quite comprehensible language of everyday life), we might recur forthwith to the warm and almost imperceptible winters of the preglacial period. But, as things stand, the stock of ice at the poles never gets melted away in the existing northern or southern summer; fresh ice accumulates on top of the old mass with each winter; prevailing winds, blowing over this ice, chill regions lying much farther toward the tropics; icebergs detach themselves and float off, thus lowering the temperature of the sea in the middle zones; arctic or antarctic currents spread round the coasts and absorb the solar heat in enormous quantities. We have only to remember the trenchant difference in England between a parching cold east wind and a mild sou'wester to realize what an immense part these polar ice caps and frozen highlands play in the production of our existing winter. Alps, Pyrenees, Himalayas, Rocky Mountains, further assist in the same