HANDBOOK OF FOSSILS. 85 



sea made countless years ago, and the tracks of worms and crabs 

 that dwelt in the mud or crawled on its surface at a time when 

 it was soft mud. The Bradford clay is a very local deposit, taking 

 its name from Bradford in Wiltshire, where it is most developed, 

 and its characteristic fossil is the pear-shaped Encrinite or "stone- 

 lily " (Apiocrinus Parkinsoni). 



c. The Great or Bath Oolite, comprising a series of shelly 

 limestones and fine Oolites, or freestones. The latter are largely 

 quarried in the neighbourhood of Bath, and used for mantelpieces 

 and the stone facings of windows. The great Oolite is rich in 

 univalve mollusca, amongst which may be noted a limpet (Patella 

 rugosa) and the handsome, tall-spired Nerituza Voltzii, numerous 

 bivalves belonging to the genera Pholadomya Trigonia, Ostrea (O. 

 gregaria), and Pecten, besides Brachiopods ( Terebratula digona, 

 which looks very like a sack of flour, and T. perovalis, etc.). 



At the base of the Great Oolite are the " Stoncsfield slates," 

 so-called a series of thin shelly Oolites, etc. , that split readily into 

 very thin slabs. They are principally of interest to geologists 

 on account of the discovery in them of the remains of small 

 insect-feeding and possibly pouched mammals. With these are 

 associated the bones of that big reptile the Megalosanrns ; the 

 flying lizards called Pterodactyles ; fish teeth and spines ; lamp 

 shells ; oysters, a Trigonia (T. iuipress'a) ; and the impressions 

 of insects, including a butterfly, and of plants. 



d. Fullers' Earth, a clayey deposit occurring in the south- 

 western parts of England, but not in the north. It abounds with 

 a small oyster (O. acuminaia) and Brachiopods (e.g. Terebratula 

 ornithocephald), etc. 



e. Inferior Oolite (including the Midford Sands). As these beds 

 are followed across the country from the south-west of England 

 to Yorkshire, they are found to change greatly in character. 

 Limestone and marine beds in the south are replaced by sandy and 

 estuarine beds in the north. Amongst other fossils from beds of 

 this agemay be found several Echinoderms, a crinkly lamp shell 

 (Terebratula frimbriata), and a spiny one(Rhynchonella spinosa), 

 bivalves belonging to the Genera Ostrea, Trigonia, Pholadomya, 

 etc., and some very handsome Ammonites (e.g. A Humphre- 

 si anus). 



4. Lias. 



This for the most part consists of very regular alternations 

 of argillaceous (clayey) limestone and clay, or shale. It is of 

 great thickness, and hence for convenience has been divided 

 into (a) Upper Lias, (b) Middle Lias or Marl-stone, and (c) 

 Lower Lias. A large number of fossils are to be found in it. 



