THEORY OF THE EARTH. 171 



This compact limestone formation is not every- 

 where covered over by chalk. Without that inter- 

 vening, it surrounds basins in several places, or 

 supports elevated flats or table lands not less wor- 

 thy of examination than those which are limited by 

 chalk. We should derive great information, for in- 

 stance, from a history of the gypsum quarries of 

 Aix, in which, as well as in those of Paris, reptiles 

 and fresh-water fishes are found ; and probably 

 land-animals will be also discovered by careful re- 

 search ; while we are assured that nothing similar 

 occurs in the entire interval between these two 

 places, which are almost two hundred leagues dis- 

 tant from each other. 



The long ranges of sand-hills which skirt both 

 slopes of the Appenines through almost the entire 

 length of Italy, contain everywhere perfectly well- 

 preserved shells, which are often found retaining 

 their colours, and even their natural pearl-like po- 

 lish, and several of which resemble those still 

 found in our seas. It would be of great impor- 

 tance to be well acquainted with these, and to 

 have all their successive strata accurately examin- 

 ed, determining the extraneous fossils found in 

 each, and comparing them with those that are con- 

 tained in other recent strata ; such, for example, as 

 those in the environs of Paris. 



In the course of this investigation, it would be 

 proper to connect the series, on the one hand, with 



