IX. 



GEOLOGICAL RELATIONS. 



Under this head we propose to make only a few re- 

 marks on the geological conditions in which such of 

 the existing species as are found also in a fossil state 

 occur, and to draw, from the few facts collected, such 

 inferences as to their former condition on the earth's 

 surface in the regions where they occur, as these facts 

 may seem to warrant. The conclusions which depend 

 upon the situation in which fossil terrestrial shells are 

 found, are however, much less worthy of confidence 

 than those derived from the marine fossils. The lat- 

 ter may reasonably be supposed to have lived and died 

 in the localities which they now occupy, while the for- 

 mer have only been preserved by being removed from 

 their original positions, and subjected to conditions en- 

 tirely different from those under which they existed 

 during life. The substance of all land-shells possesses 

 so little solidity, and their texture is so frail, that when 

 they are deprived of the protection that the animal 

 itself affords them, the operation of the elements soon 



