T2RTIARY FORMATION. 



109 



CHAPTER X. 

 TERTIARY STRATA. (Superior order, Conybeare.) 



{Supra-cretaceous Group of De la Beche.) 



Tertiary Strata — What they Include. — Lower Tertiary.—Lon- 

 don Clay.— Middle Tertiary. — M. Deshaye's Classification. — 

 Mr. Lyeil's Classification. — Eocene. — Miocene, — Pliocene. — 

 Crag.— Sections of the Thames Valley.— Thickness of Ter- 

 tiary Beds in England. 



The tertiary formations comprise all the regular 

 strata of limestone, marl, clay, and sandstone that 

 have been deposited after chalk. Before the la- 

 bours of Cuvier, these were considered as mere 

 superficial gravels, sands, or clays. The main rea- 

 son for separating the tertiary from the secondary 

 formation, is the fact that the tertiary beds contain 

 the bones of the higher order of animals, as perfect 

 in their organization as any of the existing species 

 of land quadrupeds. They are also farther re- 

 markable for the frequent alternations of beds con- 

 taining the remains of marine animals, with other 

 beds that contain exclusively the remains of land- 

 animals, and plants, and fresh-water shells : hence 

 the latter beds were denominated fresh- water for- 

 mations. 



The tertiary strata of England and France have 

 been arranged under four divisions, viz. : 



1. Lower Marine Beds. (Plastic clay and Lon- 

 don clay.) 



2. Lower Fresh-water Beds. (Marl and gypsum.) 



3. Upper Marine Formation. (Sand and sand- 

 stone.) 



4. Upper Fresh-water Formation. (Limestone 

 and silicious millstone.) 



