14 THE STORY OP THE EAETH AND MAN. 



quent action of tlie ocean as a depositor of sediment, 

 and of the internal heat as a cause of alteration and 

 movement of rocks. Against these earliest belts of 

 land the ocean first chafed and foamed. Along their 

 margins marine denudation first commenced, and the 

 oceanic currents first deposited banks of sediment ; 

 and along these first lines have the volcanic orifices 

 of all periods been most plentiful, and elevatory move-' 

 ments most powerfully felt. 



We must not suppose that the changes thus shortly- 

 sketched were rapid and convulsive. They must have 

 required periods of enormous duration, all of which 

 had elapsed before the beginning of geological time, 

 properly so called. From Sir William Thomson's 

 calculations, it would appear that the time which has 

 elapsed from the first formation of a solid crust on the 

 earth to the modern period may have been from 

 seventy to one hundred millions of years : though 

 other astronomers and physicists would, on other modes 

 of calculation, reduce this time to a much smaller 

 space ; say, to twenty or even fifteen millions of years. 

 Such a lapse of time is truly almost inconceivable, but 

 it is only a few days to Him with whom one day is as 

 a thousand years, and a thousand years as one day. 

 How many and strange pictures does this series of 

 processes call up ! First, the uniform vaporous ne- 

 bula. Then the formation of a liquid nucleus, and a 

 brilliant photosphere without. Then the congealing 

 of a solid crust under dark atmospheric vapours, and 

 the raining down of acid and watery showers. Then 



