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. 
