TERTIARY 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. Lyell'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 
superhcial 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.) 
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