312 THE TROGLODYTES. 



These are the dates of the history of our planet, and the elements of 

 what Edward Lartet called the chronology of paleontology. 



I need not speak of the Primary and Secondary geological periods, as 

 they are foreign to the chronology of man, since he did not then exist ; 

 nor need the Tertiarj^ period scarcely more arrest our attention. It is 

 true that the discoveries of M. Desnoyers in the Pliocene chalk-pits of 

 Saint Prest, show the existence of man as early as the end of the Ter- 

 tiary period in company with the southern elephant, the rhinoceros 

 leptorhinus, and the great hippopotamus; he even lived, according to 

 the Abbe Bourgeois, during the Miocene period, contemporary^ with the 

 mastodons, the predecessors of the elephants : but the latter fact is 

 doubtful ; and as to the Tertiary man of Saint Prest, he was so much 

 anterior to our troglodytes, that he need not figure in our chronology. 

 It is sufficient in the determination of our dates to commence with the 

 beginning of the Qaateruary period. 



The end of the Tertiary period was distinguished by a remarkable 

 j)henomenon, the causes of which are still imperfectly known. The 

 northern hemisphere was gradually cooled. Immense masses of ice de- 

 scended the sides of the mountains, into the valleys and plains, and 

 covered a large part of Europe, Asia, and North America, and the tempe- 

 rature of our zone, i)reviously torrid, gradually became glacial. This 

 cold period, called the Glacial period, was excessively long. After reach- 

 ing their utmost southern extent the glaciers receded considerably, and 

 then advanced again without attaining their previous limits. This was 

 the last phase of the Tertiary epoch. The Glacial period came to an end. 

 The gradual increase of temperature melted the ice, and the Quater- 

 uaiy period commenced. 



The masses of snow constituting the glaciers, which had been accu- 

 mulating for years, produced, by their melting, immense floods, which 

 bore upon their powerful waves the debris of the mountains, inundated 

 the plains, plowed the surface of the earth, excavated valleys, and 

 left in their passage large deposits of sand, clay, and bowlders. From 

 this period, called the Diluvian, date our present rivers, which give us, 

 however, but a faint idea of their former magnitude. In their now limited 

 and unchanging channels they transmit only the water which descends 

 day by day from the clouds, while the freshets occasioned by the melt- 

 ing of winter snows are of very little moment compared with those im- 

 mense inundations formerly produced when the heat of summer melted 

 not only the annual snow-s, but a part of the ancient glacier. 



The great power of the floods of water was especially remarkable dur- 

 ing the first part of the Quaternary period. It became less and less 

 until the glaciers were reduced to their present limits, and the tempera- 

 ture to its present degree. It was at this time that the phenomena of 

 great changes ceased, and the Quaternary period came to an end. Since 

 then, although mountain torrents carry with them sand and pebbles, 

 and sometimes tear from the sides of the valleys masses of considerable 



