The first theory named is that the glacial period is due to the decrease of the original heat in our climate. This theory can be dismissed by saying that the planet was cooling at the time and has been cooling ever since, and that the reasons for an ice age are greater now than then, on that theory. Another theory assumes that at some former period there was a greater amount of moisture in the atmosphere; while this of course would be the occasion for greater precipitation of snow, it does not account for the changing conditions that would produce the ice effect. That there was a preglacial period there is abundant evidence, in buried forests, the filling up and changing of river beds, and other evidences that will be referred to further on. This theory, unmodified and stated broadly, is not satisfactory. Another way of accounting for the glacial period is the change in the distribution of land and water, which is supposed to affect the distribution of heat over the earth's surface. There is much in this theory that commends itself as plausible. Another theory supposes that the land in northern Europe and America was elevated to a higher level at that time than it is now. Others attribute it to variation of temperature in space and of the amount of heat radiated by the sun. The final theory for accounting for the ice age is attributed to what is termed the precession of the equinoxes. In short, the precession of the equinoxes means that the division between summer and winter is changing gradually, so that during a period of 10,500 years the summers are growing longer in the northern hemisphere and the winters shorter. We are now in the period of long summers, but in another 10,000 years we shall be in the period of short summers and long winters. This difference of time between the winters and the summers is supposed to be sufficient to change the thermal conditions sufficiently to produce an ice age. It is true that the conditions now are very evenly balanced, so much so that in Switzerland the glaciers will increase for some years together, when the conditions will change, causing them to gradually recede. Several of the theories that have been advanced present evidences that are entitled to careful consideration, but none of them can be said to be entirely satisfactory. It is well known that the chief factors in the production of glaciers are moisture and cold. Cold alone is not sufficient; neither is moisture, unless we can precipitate it in the form of snow. Cold is opposed to the production of moisture, and this is a flaw in the argument presented by the last theory, unless we can couple with it another set of conditions which we will discuss later. The solution, if it is ever reached, is perhaps more likely to be found in the realm of meteorology than geology.