138 LIFE ON THE EARTH. 



calculation, but it lies quite beyond the power of the 

 mind to contemplate with steadiness. 



Abandoning all further attempts to determine the 

 probable antiquity of the Strata, and the several 

 races of Life, in measures of solar time, we may re- 

 fer to some more limited trials to assign a date to 

 the origin of the present physical aspect of nature 

 the present action of the sea on its coasts, and of the 

 rivers on their beds. In the speculations of De Luc 

 concerning natural chronometers this period is de- 

 scribed as posterior to the existence of our conti- 

 nents, and as having a fixed chronology; it is now 

 regarded as the latest of the Pleistocene periods ; in 

 the northern zones of the world it is the Postglacial 

 period; and it includes, according to all observation 

 and opinion, the age of the human race. 



Herodotus, the first author who ventured an 

 estimate of this kind, was naturally conducted to it 

 by his inquiries regarding the ancient history of 

 Egypt. This fertile country, 'the gift of the Nile,' 

 offered him, in the real and fabulous narrative of its 

 governors, a long series of centuries of elapsed time, 

 and in the periodical floods and corresponding rise 

 of its surface and growth of its delta, natural chro- 

 nometers by which in some degree to check the tra- 

 ditions of the priests. 



The conclusion of Herodotus does not however 



