48 Astronomy and Geology compared. PT. i. 



events that the past is linked to us. There is another 

 feature which distinguishes Greology from Astronomy 

 under this aspect. There is not one tittle of evidence 

 in Geological science to show that the changes it 

 exhibits have anything of a cyclical or periodically 

 recurrent character. Ichthyosauri or Plesiosauri, 

 Mastodons and Megatheriums, have disappeared from 

 the Earth for ever ; there is not the slightest proba- 

 bility that we shall ever revert to the state of things 

 in which they had their being. Not only does one 

 organisation gradually supplant and efface a preceding 

 one, but viewed as a whole there is a constant advance 

 in the structure of the animal life, the links of which 

 are thus handed down to us. Some of the earlier 

 formations are composed of conglomerations of shell- 

 fish, the very lowest forms of life of which we have 

 cognizance. What an immense advance is indicated 

 in the fossil remains of the animals of a later date, 

 showing that they like ourselves were furnished with 

 the organs of sight and of hearing, which continue 

 to be after so many ages the great avenues of per- 

 ception. These senses mark a vast increase in the 

 faculties of the beings who possess them. In order 

 to make use of these senses these animals must have 

 been endowed with instinct, that mysterious faculty, 



