431 



Feet. 

 12. Sandstones and shales containing no well-preserved 

 plants, but about 90 feet from the top a bed of coal 

 1 foot thick 170 



The plants of this system differ from those of the upper sandstone 

 and shale by the abundance of PterophyUum minus, Otopteris acumi- 

 nata, Sphenopferis hymenophylloides, and the deeply lobed Cyclopteris 

 digitata, and is characterized by PterophyUum pectinoides, Equisetum 

 laterale, Lycopodytes falcatus, and by a singular frond supposed to 

 belong to a Cycadean plant. With respect to the vertical Equiseti in 

 bed 5, Mr. Williamson is of opinion that they did not grow where 

 they are found, but were transported, not, perhaps, from a great 

 distance ; and that their perpendicular position is owing to the roots 

 of this description of plants being specifically heavier than the stem, 



3. The Great or Bath oolite varies very little in its characters Or fos- 

 sils, except for 8 or 9 feet from the top, where, according to Mr. 

 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 upper beds Cayton and Gristhorpe Bays. 



Section of the general structure of the Great Oolite. 



Feet. 



1. The 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 Ostrea edulina, 

 Amphidesma decurtatum, Mya calceiformis, a large 

 undescribed Ammonites, and at the junction with 

 the next bed Belemnites compressus, B. Aalensis, 

 Melania Heddingtonensis, Amphidesma decurtatum, 

 Serpulse, 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, whichare mostabundantat 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 composita, Acieon 

 glaher, Terehra vetusta, Pliasianella cincta, Trochus, Avicula Braamhurien- 

 sis, Gervillia acuta, Cucullea cancellata, Astarte minima, Cardita similis, 

 Pholadomya acuticostata. 



4. Nodular ironstone, sometimes inclosing fragments of 



Ammonites Blagdeni 6 to 12 in. 



5. Clay containing Avicula Braamburiensis, Amphidesma 



decurtatum, and a Gervilia 1 ft- 



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



stone and argillaceous oolite 3 



voi^. II. 2 H 



