This process, so slightly indicated here, extended over a vast period of time. It is supposed that later, for a protracted period, rain fell. When the age of rain had passed, the deep depressions in the earth's surface were left filled with water--our present oceans and some of the seas. It would be impossible for us to review rapidly all the stages through which the earth passed in its making. Suffice it to say that conditions upon it were not always favorable to life as we know it. In course of long geological ages--perhaps millions and millions of years--forests of trees, plants, shrubs and flowers sprang up and covered the bare earth. Last of all, probably, _man_ appeared. How all these things came about no one understands, but it is generally accepted that they occurred in an order similar to that just given. It would be useless for us to inquire into all the reasons that have led to these conclusions, but the most important one has been _evidences within the earth itself_. Men who work deep down in mines know that as they descend lower and lower, the temperature rises, until there is a noticeable difference between the temperature at the entrance of a mine and at its lowest point. Moreover, not infrequently volcanoes pour forth streaming lava, smoke and fire accompanying the eruption. While such evidences lead to the conclusion that the temperature of its interior is very high, still there are many reasons for believing that the earth is a solid mass. From the examination of the various earth strata, their composition and the evidences each bears of the conditions under which it was formed, we learn of periods of rain, heat and cold prevailing. All these facts belong to the realm of geology however, and concern us here only as they have concerned the progress of mankind. These same earth layers or strata which preserve eloquent testimony regarding the earth's development, contain also remains of prehistoric men--men who lived in the far away time before records were made and of which the rocks alone give testimony. Of the beginnings of the human race we know nothing. Many scientists, notably Darwin and his followers, have sought to show that man evolved from some lower animal life, in a way similar to that in which we find some plant or flower perfected from inferior origin. Whether the theory of man's evolution from some lower animal will ever be shown to be true the future alone can tell. Nevertheless the scholarly world today has generally accepted the evolutionary view of life and the world. Buried within the earth along river-beds, around cliffs, in mounds and many other places, have been found remains of primitive man. While the beginnings of the human race, as has been said, are utterly unknown, the earliest stage of which we have knowledge has been called the Paleolithic Age,--the age of the River-drift Man.