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794 STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
cient in some forms of hfe which were no doubt abundant in neighbour- 
ing areas of clearer water. Thus there are hardly any corals, and few 
echinoderms, polyzoa, or brachiopods. Some lamellibranchs are abundant, 
particularly Gryphea and Ostrea (both forming sometimes wide oyster- 
beds), Lima, Avicula, Pecten, Astarte, Trigonia (clavellata), Nucula (N. nuda, 
N. Phillipsii)—the whole having a great similarity to the assemblages 
in the Lower Oolite formations. The gasteropods are not so numerous 
as in the calcareous beds below, but belong mostly to the same genera. 
The ammonites, especially of the Ornatus and Armatus groups, are 
plentiful,—A. Duncan, A. Elizabethe (Jason), A. Lamberti, and A. oculatus, 
A. ornatus, A. athleta, being characteristic. The belemnites, which also 
are frequent, include B. hastatus (found all the way from Dorsetshire to 
Yorkshire), also B. puzosianus. The fishes include the genera Astera- 
canthus, Hybodus, Ischyodus (Egertoni), aud Lepidotus. 'The reptilian 
genera Ichthyosaurus, Megalosaurus, Plesiosaurus (4 species), Steneosaurus, 
Pliosaurus, and Rhamphorhynchus have been noted. 
(2.) Corallian, traceable with local modifications from the coast of 
Dorset to Yorkshire. The name of this group is derived from the 
numerous corals which it contains. According to the recent exhaustive 
researches of Messrs. Blake and Hudleston,! this group when complete 
consists of the following subdivisions : . 
6, Supra-Corallian beds—clays and grits, including the Upper Calcareous Grit 
of Yorkshire, and the Sandsfoot clays and grits. 
5. Coral Rag, a rubbly limestone composed mainly of masses of coral. 
4, Coralline Oolite, a massive limestone in Yorkshire, but dying out southwards 
and reappearing in the form of marl and thin limestone. 
3. Middle Calcareous Grit, probably peculiar to Yorkshire. 
2. Lower or Hambleton Oolite, not certainly recognized out of Yorkshire. 
1. Lower Calcareous Grit. 
The corals are found in masses in their positions of growth, forming 
true massive coral-reefs in Yorkshire ( Thamnastrea, Isastreea, Thecosmilia, 
Rhabdophyllia (Fig. 365] ). Numerous sea-urchins occur in many of the 
beds, particularly Cidaris florigemma (Fig. 367), also Pygurus, Pygaster, 
Hemicidaris, &c. Brachiopods are comparatively infrequent. The 
lamellibranchs are still largely represented by Avicula, Lima, Ostrea, 
Pecten, and Gryphza (Ostrea gregarea and Gryphza dilatata being specially 
numerous). Among the Ammonites are A. catena, A. cordatus, A. ingens, 
A. perarmatus, and A. plicatilis. 
The Upper or PortLanp Oo.irss bring before us the records of the 
closing epochs of the long Jurassic period in England. They are di- 
visible into three groups: (1) Kimmeridgian, at the base; (2) Port- 
landian, and (3) Purbeckian. 
(1.) Kimmeridgian, so named from the clay at the base of the 
Upper Oolites, well developed at Kimmeridge, on the coast of Devonshire, 
whence it is traceable continuously, save where covered by the Chalk, 
into Yorkshire. According to Mr, J. F. Blake it may be subdivided 
into two sections : 
(b.) Upper Kimmeridgian, consisting of paper-shales, bituminous shales, cement 
stone, and clays, characterized by a comparative paucity of forms but 
an infinity of individuals; perhaps 650 feet thick in Dorsetshire, but 
' On the Corallian Rocks of England. Q. J. Geol. Soe. xxxiii. p. 260. 
