Part iil. Sect. ii. § 2.] JURASSIC. 793 
\ 
But the most important organic relics from this geological horizon are 
the marsupial mammalia already referred to. 
The fauna of the Great Oolite includes a number of corals (Isastrza, 
Cyathophora, Thamnastrea), echinoderms, particularly of the genera 
Acrosalenia, Clypeus, Echinobrissus, and Pseudodiadema ; numercus polyzoa 
(Diastopora, &c.), brachiopods of the genera RBhynchonella (RB. concinna, 
i. obsoleta), and Terebratula (T. digona, T. globata, T. maxillata); lamel- 
libranchs, particularly species of Gervillia, Lima, Ostrea, Pecten, Arca, 
Astarte, Cardium, Ceromya, Cypricardia, Myacites, Pholadomya, Tancredia ; 
gasteropods of the genera Actzonina, Nerinea, Nerita, Buccinum, Murea, 
Fusus, Patella, &c., and cephalopods, which, however, are comparatively 
rare. Some of the same genera of fishes occur as in the Inferior Oolite, 
and a number of the same genera of reptiles. The Bradford Clay of 
Wiltshire has long been well known for its pear-encrinites (Apiocrinites 
rotundus), which are found at the bottom of the clay with their base 
attached to the top of the Great Oolite limestone. 
The Cornbrash is traceable by some species peculiar to or specially 
abundant in it, as Hchinobrissus clunicularis, E. orbicularis, Holectypus 

Fic. 387.—MIppDLE Jurassic AMMONITES. 
a, Ammonites (Aspidoceras) perarmatus (Sby.) (4); b, A. (Amaltheus) Lamberti (Sby.) ; 
c, A. (Cosmoceras) Jason (Zeit.) (4); d, A. (Cosmoceras) calloviensis (Sby.) (3). 
depressus, Terebratula obovata, T. lagenalis, Avicula echinata, Gervillia avicu- 
loides, Ammonites macrocephalus (Hervey?). 
The Mipp.z or Oxrorn Oo.ires are composed of two distinct groups : (1) 
the Oxfordian, and (2) the Corallian. 
(1.) Oxfordian, divisible into two sections: (a) a lower zone of 
calcareous abundantly fossiliferous sandstone, known, from a place in 
Wiltshire, as the Kellaways Rock (Callovian). This zone, after dying 
out in the midland counties, reappears in Lincolnshire and attains a 
thickness of 30 feet on the Yorkshire coast. It contains about 150 
species of fossils, of which nearly a half are found in lower parts of the 
Jurassic series, and about the same number pass upward into higher 
zones. Among its characteristic forms are Ammonites calloviensis, 
A. gowerianus, A. modiolaris, A. macrocephalus, Belemnites Oweni, Avicula 
mequivalvis, Gryphea bilobata ; (b) Oxford Clay—so called from the name 
of the county through which it passes in its course from the coast of 
Dorsetshire to that of Yorkshire—consists mainly of layers of stiff blue 
and brown clay, sometimes attaining a thickness of 600 feet. From the 
nature of its material and the conditions of its deposit, this rock is defi- 
