508 CENOZOIC TIME MAMMALIAN AGE. 



being attended with a change in the living species of the waters,, 

 encroaching fresh waters destroying the marine species, and so on. 

 By considering carefully all the various conditions incident to a 

 coast from these sources, the ever-varying character of the Tertiary 

 beds will be appreciated. 



The rocks are of the following kinds : — beds of sand or clay, so soft 

 as to be easily turned up by a shovel ; compact sandstones, useful for 

 a building-stone, though not very hard ; shell-beds of loose shells 

 and earth, the shells sometimes unbroken, in other cases water- 

 worn ; shell-rocks and calcareous sandstones, consisting of pulverized 

 shells and corals firmly cemented and good for building-stone, as 

 at St. Augustine ; marls, or clays containing carbonate of lime from 

 pulverized shells, and hence effervescing with the strong acids ; 

 compact solid limestones, sometimes oolitic in structure ; buhrstone, a 

 cellular siliceous rock, valuable for millstones, as in South Caro- 

 lina. The clays and sand-beds often contain lignite (or brown coal 

 derived from vegetation), and are then called Lignite beds. 



Although the Tertiary rocks are generally less n>m than those 

 of the Palaeozoic, there are in some places hard slates and sand- 

 stones not distinguishable from the most ancient. Such rocks 

 occur in California, in the vicinity of San Francisco ; and it has 

 been suspected that some crystalline rocks of the region are altered 

 Tertiary strata. 



There are also beds of whitish earthy or chalky aspect, which 

 consist of siliceous Infusoria, and others, of the shells of Khizo- 

 pods. 



Claiborne, Jackson, and Vichsburg Epochs. — Eocene. — The Tertiary beds which 

 contain only extinct species of fossils, and are therefore called Eocene, occur in 

 Maryland, Virginia, North and South Carolina, and the States bordering on 

 the Gulf of Mexico. The beds of the several epochs are best displayed and 

 most distinct in Mississippi and Alabama. 



The beds of the Claiborne epoch, or Lower Eocene, well developed about 

 Claiborne, Alabama, consist, beginning below, of (1) Clay, 25 feet, overlaid by 

 a bed of lignite, 4 feet; (2) Marl with oysters (0. sellseformis) ; (3) Marly are- 

 naceous limestone; (4) Marl with oysters; (5) Sand with shells partly showing 

 a beach-origin, often called the " Orange-sand" group in the region. Whole 

 thickness, about 125 feet. 



In Mississippi, according to Hilgard, there are (1) the Northern Lignitic 

 group, consisting in some places, at base, of small estuary deposits with marine 

 shells, and above of clays and sands with Lignite and fossil leaves, — covering a 

 large part of the northern half of the State; and the Lignitic group of N. Lau- 

 derdale, — the latter overlaid by (2) Siliceous Claiborne beds, sandstones and 

 claystones, in Lauderdale, Newton, etc., near middle of western half of the 

 State; (3) Lignitic clays of N. Clarke co. ; (4) Calcareous beds, white and 



