98 MEMOIRS OF 



stroyed them : the cause, therefore, has been as 

 sudden as the effect it produced." 



The ideas of M. Cuvier on the relative ages 

 of the strata of deposited soils, extending even 

 to different chains of mountains, have led to the 

 present system adopted by geologists, and from 

 them it may be concluded, that " all these 

 layers of deposited soils having been necessarily 

 formed in a horizontal position, the most ancient 

 are those which have been more or less raised 

 towards a vertical line by some catastrophe, and 

 the most recent are, on the contrary, the hori- 

 zontal layers ; because, having preserved their 

 original situation, it is evident that they could 

 only be formed after the revolution which 

 changed the position of those whicli are oblique, 

 which they more or less cover, and on which 

 they rest." 



One of the most important questions treated 

 of in this work is that of the alteration in animal 

 forms ; whether the forms of lost animals, which 

 differ so much from those which are now living, 

 really indicate species and genera distinct from 

 species and genera now existing, or if time alone 

 has modified the primitive forms, so as to attain 

 the present form. The examination of this 

 question alone would give a satisfactory answer 



