244 MOLLUSCA. 



and trace in the mineral kingdom the proofs of those changes 

 which animals and vegetables have experienced. In the 

 meantime, we would recommend the examination of the 

 laws which regulate the physical and geographical distribu- 

 tion of recent shells and molluscous animals, as the most 

 suitable preparation for investigating the condition of those 

 extinct races, the memorials of which are preserved in stra- 

 ta, differing from one another in structure, in position, and 

 in composition. 



