TERTIARY FORMATIONS. 



219 



south-east is impressed on the summits {caps), and in the direction of 

 the principal hills. In one word, no country can afford more instruc- 

 tion respecting the last revolutions, which have terminated the for- 

 mation of the present continents." 



Though chalk is the foundation rock of the country, for a consid- 

 erable extent round Paris, being covered by tertiary strata, it rises 

 to the surface only in a few situations. The total thickness of the 

 tertiary strata over the chalk, as given in an ideal section of the coun- 

 try, is nearly five hundred feet.* 



Many of the tertiary beds in the Paris basin are not found else- 

 where, and therefore cannot be taken as types of other tertiary for- 

 mations ; and the lower bed, called the plastic clay, is but very im- 

 perfectly developed near Paris. In attempting to generalize the ter- 

 tiary formations, a difficulty presents itself, if we are to class them by 

 their zoological characters ; for some of the formations, which in cer- 

 tain situations, contain, exclusively, the remains of marine animals, 

 present, in other places, river or lake shells, with wood and the bones 

 of land animals. It is, therefore, probable, that while the waters in 

 one lake or basin might be saline, those in another lake might be 

 fresh ; and two cotemporaneous formations may hence contain very 

 different organic remains. 



The tertiary strata in England and in the north of France, may 

 be arranged under four divisions, which are given below : after de- 

 scribing these, the more recent tertiary strata, called by some French 

 geologists Quaternary, will be noticed in the following Chapter. 



TERTIARY FORMATIONS. 



1. Lower Marine Beds. 



Sometimes intermixed with 

 freshwater beds. 



a Argdlaceous and Sandy de- ) ^ .7 ^ ^ ^ j- - - t 

 Di /^i o J ( '^rs'ile et trres tertiaires a li^- 

 posits, rlastic day, band, > ^. ° 



LiOndon Clay ) 



b Lower Marine Limestone Calcaire grossier. 



* The following ascending series of beds of the Paris basin was first given as a 

 correct account of their succession : more extended observations have proved that 

 the position of No. 3, or the Calcaire siliceux, is higher in the series. 



1. Plastic Clay and Lower Sand. ^ 



2. Calcaire grossier. 



3. Calcaire siliceux and Sandstone. 



4. Gypseous Marl. 

 Gypseous with Bones. 

 Upper gypseous Marl. 



5. Sandstone and Sand without Shells. 

 Upper Marine Sandstone. 

 Millstone without Shells. 



6. Freshwater Limestone, including Marls, and Millstone, with freshwater 



Shells. 



7. Alluvial Soil, ancient and modern, including Pebbles, Pudding-stone, Black 



Earth {les marnes argilleuses noires), and Peat. 



