140 Geological Socielj/. 



Williamson's observations, it presents two forms very different both 

 in structure and organic remains. The localities referred to in the 

 memoir for the general structure of the formation are Cloughton and 

 White Nab, and for the u}3per beds Cay ton and Gristhorpe Bays. 



Section of the general structure of the Great Oolite. 



Feet. 



1. T\\e lowest beds consist of a very hard blue lime- 



stone, sometimes oolitic and destitute of fossils, 

 except in the upper part, where the stone is softer, 

 and where the author has found Osirea edulina, 

 Amphidesma decurtatumy Mya calceiformis, a large 

 undescribed Ammonites, and at the junction with 

 the next bed Belcmnites compressus, B. Aalensis, 

 Melania Heddingtonensis, Amphidesma decurtatumy 

 Serpulae, and long tuberculated spines of a Ci- 

 daris, but no portion of the Cidaris itself. ... 14 to 20 



2. Hard blue fine-grained oolite, sometimes ironshot, 



and apparently devoid of organic remains 6 



3. Soft or hard bluish clay, tinged, at some localities, 



with iron. It contains at least 1 1 species of fossil 

 shells,which are most abundant at Cloughton Wyke, 

 and some species which occur there have not been 

 noticed at any other point. This bed also contains 

 the remains of a Saurian, which the author is in- 

 duced to consider a new species of Plesiosaurus. . 2 

 The shells given by Mr. Williamson are, Rostellaria co7nposita, Acteon 

 glaher, Terehra vetusia, Phasianella cincta, Trochus, Avicula Braamhurien- 

 sis, Gervillia acuta, Cucidlea cancellata, Astarte Jiiinima, Cardila similis, 

 Pholadomya acuticostata. 



4. Nodular ironstone, sometimes inclosing fragments of 



Ammonites Blagdeni 6 to 12 in. 



5. Clay containing Avicula Braamhuriensis, Amphidesma 



decurtatum, and a Gervilia 1ft. 



6. The top strata consisting of layers of nodular iron- 



stone and argillaceous oolite 3 



The lower part of this bed is characterized by the presence of Perna 

 quadrata, and the upper by numerous remains of the following shells: 

 Melania Heddingtonensis, Ammonites Blagdeni, Terehratula spinosa, Gjy- 

 phcBa nana, Ostrea Marshii, Pecten lens, Plaaiostoma interstinctum (c)*, Avi- 

 cula Braamburiensis (c), A. echinata{c) ? Gervilia acuta (c), Trigonia cos- 

 tata, T. clavellala, Astarte minima (c), Corbula deprcssa, Pinna cuneata, 

 Pentacrinites vulgaris, Cidaris vagans. 



The author then describes the upper beds of the Great Oolite at 

 the two extremities of Cayton Bay, and at low water at the south 

 side of Carnelian Bay. 



Top. Irony nodules, without organic remains 1 ft. 



Extremely hard ironshot rock, composed almost wholly 

 of fragments of fossils, viz. Millepora straminea, pa- 

 pillae of a Cidaris, innumerable small spines, probably 



• (c) The species thus distinguished are found in the greatest abundance. 



