Ch. XVIII.] 



PARIS BASIN, 



243 



eighty miles in its greatest length from north-east to south- 

 west, and about ninety miles from east to west. This space 

 may be described as a depression in the chalk (see diagram 

 No. 2, p. 16), which has been filled up by alternating groups 

 of marine and fresh-water strata. MM. Cuvier and Brong- 

 niart attempted in 1811 to distinguish five different formations, 

 and to arrange them in the following order, beginning with the 

 lowest : 



{Plastic clay. 

 Lignite. 

 First sandstone. 

 2. First marine formation Calcaire grossier. 



{Siliceous limestone. 

 Gypsum, with bones of animals. 

 Fresh-water marls. 

 f Gypseous marine marls. 



4. Second marine formation. . . . .< Upper marine sands and sandstones. 



I Upper marine marls and limestones. 

 r Siliceous millstone, without shells. 



5. Third fresh-water formation. < Siliceous millstone, with shells. 



'Upper fresh-water marls. 



These formations were supposed to have been deposited in 

 succession upon the chalk ; and it was imagined that the waters 

 of the ocean had been by turns admitted into and excluded 

 from the same region. But the subsequent investigations of 



No. 58. No. 59. 



M. Alex. 

 Bronguiart M. Constant Prevost. 



