1 90 Portland Beds. 



A shell peculiarly characteristic of the Kimeridge Clay 

 is a large oyster, Ostrea deltoidea, Fig. 40. Shells of the 

 genera Rhynchonella (Rh. inconstans) and Terebratula, 

 Discina (D. Humphresiana, &c.), Lingula ovalis, 

 Pinna, Astarte, Pecten, Trigonia (T. incurva), and 

 other bivalves, and Ammonites and Belemnites, are 

 also common, the Belemnites sometimes almost paving 

 the ledges of the seashore in Kimeridge Bay. Fishes 

 of the Oolitic genera already named, with others, are 

 found, and many remains of reptiles, among others 

 Turtles, Crocodiles of the genera Goniopholis, Teleo- 

 saurus and Steneosaurus, 5 species of Ichthyosaurus, 

 8 of Plesiosaurus, and 5 of Pleiosaurus, some of the 

 last of great size. Cetiosaurus longus and Megalo- 

 saurus Bucklandi also occur. Fragments of wood are 

 not uncommon. 



The PORTLAND LIMESTONE and SAND lie above the 

 Kimeridge Clay. The best sections of these rocks 

 occur in the Isle of Portland, as shown in fig. 39, 

 p. 187. The sand which forms the base of the forma- 

 tion, is there 150 feet thick, and the limestone about 

 70. Of this, about 20 feet forms marketable stone 

 in three horizons, from the best part of which the 

 celebrated Portland stone is derived, used in many 

 public buildings, of which St. Paul's may be cited 

 as an example. The limestone, like those of most 

 other Oolite formations, is cream-coloured, and gene- 

 rally fossiliferous. Among the most common forms 

 found in it are Trigonia gibbosa and T. incurva, 

 Pecten lamellosus, Ostrea expansa, Cardium dissimile, 

 Terebra Portlandica, and various AmmowUes, some of 

 them of large size. The lowest beds are full of layers 

 of flint and chert. The sand is fossiliferous, containing 

 Oysters, Cardiums, &c. The Portland stone also occurs 



