zio THE POPULAR SCIENCE MONTHLY. 



with all it contains, and all the materials that compose it, began as a 

 vast, vaporous mass diffused in space. It was a globe of vapor. 

 When the process of cooling set in, this mass became liquid, and, dur- 

 ing periods of time which we cannot compute, it was only a vast mass 

 of rocks and of matter melted by fire. 



It is needless to insist on the fact that, at this epoch, on the surface 

 of our globe, there were no living beings, and consequently no men. 



The cooling progressing, there is formed a pellicle on the surface of 

 the globe, and this pellicle goes on increasing in thickness. This is what 

 we will call the primitive earth. On this primitive earth, during a long 

 period, water could not exist in a liquid state, and consequently there 

 were as yet upon our globe no living beings, for all these beings need 

 water ; and, of course, no men. 



But the process of cooling continued. The water which was vapor- 

 ized in the atmosphere fell in torrents on this crust which enveloped 

 the globe ; chemical reactions, of a violence of which we can form no 

 idea, were produced. At this moment began the formation of what we 

 call the earth of transport, and the globe entered upon what is called 

 the Secondary epoch. 



Strictly we may say that, from the moment the waters rested 

 in a liquid state upon the surface of the earth, life might begin to 

 manifest itself. In certain thermal waters of high temperature, we 

 find conferva? microscopic vegetables which are already organized 

 and living. But no animal could yet live in this medium, for the heat 

 would coagulate its albumen. Later, the cooling always pi*ogressing 

 and the sea enveloping the greater part of the globe, more complex 

 vegetables appeared. Soon animals, chiefly aquatic, made their ap- 

 pearance, and among them I would mention those gigantic reptiles you 

 have sometimes seen represented in certain book announcements on 

 the walls of Paris. Mammals man could not yet inhabit our globe. 



As the cooling progressed, continents were formed by the upturn- 

 ings of Nature. The time came when true mammals and birds, analo- 

 gous to living species, appeared in their turn. This was the commence- 

 ment of the Tertiary epoch. Then, very probably, man might have 

 lived. We shall presently have to ask if he did not exist, at least in 

 the latter part of this period. 



The dislocation of the crust of the globe elevated the mountains, 

 dug the valleys, sank the seas, formed the continents, and, toward the 

 end of the Tertiary period, the globe presented a surface much resem- 

 bling what we see now. Here commences the Quaternary period. 

 This quaternary period presents to us a very remarkable phenome- 

 non. 



Up to this time, putting out of account the slight oscillations that 

 have occurred, the globe seems to have cooled in a nearly uniform 

 manner, from the time when it formed only a mass of vapor, down to 

 the Tertiary epoch. With the Quaternary period came a moment 



