GEOGNOSY AND GEOLOGY. 367 
produced in the same way. Clays and marls accompany it, and separate the 
various lime strata. Subordinate masses are sandstones, gypsum, karstenite, 
rock salt, and carbonaceous masses. This group is divisible into three 
principal divisions. 
The Lower Oolite. This is bounded inferiorly by the lias, superiorly by 
the Oxford clay, and embraces marly, sandy, compact, or oolitic limestones, 
and also true oolite, whose beds alternate with clays and marls. The 
limestones are generally light-colored, turning to ferruginous in exposure, 
this being caused by the presence of carbonate of iron. Bitumen causes a 
grey color. In England this division includes conspicuous beds of fuller’s- 
earth. The sandstones are conglomeratic,.calcareous, marly, , and 
ferruginous, with veins of fibrous carbonate of lime and arragonite ; some 
are finely granular and quartzose, or passing into argillaceous quartz. 
Argillaceous sphzerosiderite and oolitic marls are subordinate species. 
The thickness of the oolite of the Jura amounts to from 1000 to 3000 
feet. In England, where the formation is highly developed, the following 
succession of strata occurs. Lowermost of all is the inferior oolite, 
separated from the great or Bath oolite by an immense bed of clay, 
exhibiting the character of fuller’s-earth (Terre a foulon). This great oolite 
is a partly compact oolitic, partly coarsely granular limestone, containing 
entire beds of corals. Between the great oolite and the fuller’s-earth there 
is, in the vicinity of Stonesfield, a bed consisting of marly sandstones and 
loose sand, with many concretions. This is the so-called Stonesfield slate, 
interesting from its containing the first remains of fossil mammalia. Next 
to the great oolite comes a stratum of marly clay, becoming sandy above, 
the Bradford clay, of a blue color, upon which rests the Forest marble, a 
limestone full of shells. On the Forest marble lies a thin stratum of slaty, 
coarsely granular limestone, the Corn-brash. Belemnites giganteus and 
canaliculatus, Ammonites Macrocephalus, &c., are characteristic fossils. 
The middle formation, which embraces the Oxford clay and the coral-rag, 
contains purer compact limestone of white or ochre yellow color, calcareous 
slate or lithographic stone; oolitoid limestone, which les intermediate 
between compact and oolitic, and often entirely filled with fossils; marble 
of various colors; mar] and marl lime, of darker colors, owing to the 
presence of carbonaceous matter; dolomite and sandy limestone. 
Subordinated are iron-stone in rounded great or small grains, gypsum, 
karstenite, rock salt, and coal of poor quality. | 
Immediately on the upper layers of the English inferior oolite there lies 
a stratum consisting of calcareous concretions cemented by marl, and 
bearing the name of the Kelloway rocks. Upon these lies a blue clay, the 
Oxford clay, containing thin lime and marl beds, and _ calcareous 
concretions. Next comes the calcareous grit, a calcareous loose sandstone. 
This is succeeded by the coral-rag, and this by the pisolitic lime, an oolitic 
limestone w:th grains and nodules of iron-stone. 
The fossils characteristic of this group are Avicula pectiniformis, the 
corals of the coral-rag, Astrea helianthoides, Melania striata, &c. 
The upper formation [ Kimmeridge clay and Portland oolite| contains pure 
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