CHAPTER XII 

 THE HARDENING OF ROCKS 



A^TER the time when the great overflows of lava 

 took place, spreading over continents and some- 

 times seas, there was an era when the explosions 

 and outbursts began to diminish in violence, and the 

 world slowly settled down to conditions something like 

 those which we see in our own day. The seas were 

 forming ; there was rainfall and summer and winter on 

 the earth. The rains and the winds, the summer heats 

 and winter snows were more violent than now, and 

 the volcanic activity of which we have spoken was much 

 more fierce than anything of which mankind has any 

 recollection. In the British Isles the rainfall in a year 

 averages something in the neighbourhood of thirty inches. 

 In some regions of the earth it is as much as four times 

 that amount, and deluges of fifteen inches have fallen in 

 a day. But in the era of which we have spoken deluging 

 rains that were to be measured in feet rather than inches 

 fell incessantly. The air was saturated with moisture, 

 and it no sooner descended on the warm earth than it 

 steamed back to the clouds again. For reasons not unlike 

 these, nor unconnected with them, the great currents of 



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