246 INTERACTION OF NATURAL FORCES. 



the remains of Egypt and Assyria we gaze upon with silent 

 astonishment, and despair of being able to carry our thoughts 

 back to a period so remote. Still must the human race have 

 existed for ages, and multiplied itself before the pyramids of 

 Nineveh could have been erected. We estimate the duration 

 of human history at 6000 years ; but immeasurable as this time 

 may appear to us, what is it in comparison with the time dur- 

 ing which the earth carried successive series of rank plants 

 and mighty animals, and no men ; during which in our neigh- 

 bourhood the .amber-tree bloomed, and dropped its costly gum 

 on the earth and in the sea ; when in Siberia, Europe and 

 North America groves of tropical palms flourished ; where 

 gigantic lizards, and after them elephants, whose mighty re- 

 mains we still find buried in the earth, found a home ? Dif- 

 ferent geologists, proceeding from different premises, have 

 sought to estimate the duration of the above creative period, 

 and vary from a million to nine million years. And the time 

 during which the earth generated organic beings is again 

 small when we compare it with the ages during which the 

 world was a ball of fused rocks. For the duration of its cool- 

 ing from 2000 to 200 centigrade, the experiments of Bishop 

 upon basalt show that about 350 millions of years would be 

 necessary. And with regard to the time during which the first 

 nebulous mass condensed into our planetary system, our mos* 

 daring conjectures must cease. The history of man, there 

 fore, is but a short ripple in the ocean of time. For a much 

 longer series of years than that during which man has already 

 occupied this world, the existence of the present state of in- 

 organic nature favourable to the duration of man seems to be 

 secured, so that for ourselves and for long generations after 

 us, we have nothing to fear. But the same forces of air and 

 water, and of the volcanic interior, which produced former 

 geological revolutions, and buried one series of living forms 

 after another, act still upon the earth's crust. They more 

 probably will bring about the last day of the human race than 



