THE WORLD BEFORE MAN 25 



continental period, when the land of the northern 

 hemisphere was higher and more extensive than at 

 present. It was also a time of great physical change, 

 when much erosion of valleys and sculpturing of the 

 surface of the land occurred, and when extensive earth 

 movements and ejections of igneous rock increased 

 the irregularity of the surface and gave greater variety 

 and beauty to the land. The pliocene was altogether 

 a most important period for giving the finishing 

 touches of physical geography, and in it several 

 modern species of land animals were introduced ; but 

 we have as yet, as we shall find in the sequel, no 

 certain evidence that man was a witness of the move- 

 ments and sculpturing of the earth's crust, so im- 

 portant in the preparation of his future home, though 

 statements to this effect have been made on grounds 

 which we shall have to consider. 



In the course of the pliocene the previously high 

 temperature of the northern hemisphere was sensibly 

 lowered, and at its close the pleistocene period intro- 

 duced a cold and wintry climate, along with gradual 

 and unequal subsidence of the land, the whole pro- 

 ducing that most dismal of the geological ages, known 

 as the * glacial period.' At this time much of the 

 lower land of the continents was submerged and the 

 mountains became covered with snow and ice, leaving 

 space for vegetable and animal life only toward the 

 south and in a few favoured spots in the higher 

 latitudes. There is much difference of opinion 

 among geologists as to the extent, duration and 



