CORALLIAN BEDS. 32/ 



Some of these divisions are local. The entire thickness in York- 

 shire varies from 200 to 250 feet. 



The Upper beds contain Ostrca ddtoidca, and pass up into the 

 Kinieridge Clay; and the lower beds contain Grypluca dilatata, and 

 pass down into the Oxford Clay. The term 'grit,' applied to these 

 rocks, is not usually appropriate, as they are ferruginous marly 

 sandstones, with cherty limestone, in Yorkshire ; and occasionally 

 the 'grits' are oolitic. Clays occur in the lower beds in York- 

 shire, and are conspicuously developed in the series in Dorset- 

 shire. 



Among the fossils are the Corals Thecosmilia annularis, Tham- 

 nasircEa arachnoides, T. concinna, Isasfnxa explanafa, Comoseris 

 irradians, Stylina De la BecJm, S. tubifcra, etc., and these some- 

 times, as in parts of Wiltshire, form a kind of reef, and retain the 

 position in which they grew. In their forms, as remarked by 

 Lyell, they more frequently resemble the reef-building Polyparia of 

 the Pacific than do the Corals of any other member of the Oolitic 

 series. The Coral Rag is in fact made up of coral-reefs, and more 

 especially the debris of coral-reefs, shell-beds, huge sand-banks, 

 and mud deposits. The fossils naturally vary in different places, 

 and at different horizons. The MoUusca include Avimonites verte- 

 bralis, A. cordatus, A. plicatilis, dead A. pcrarmatus {catena), the casts of 

 whose chambers are not uncommon in the lower beds in Berks and 

 Wilts ; Behmnites abbreviaius, which attains a large size ; Gcrvillia 

 aviculoides, Pholadomya pancicostata, Ostrea solitaria, O. gregaria, O. 

 Manhii, Myacites seairiformis, Lima pectiniformis, Trigonia clavcllata, 

 T. monilifera, Penia quadrata. Pinna lanceolata, Gonio?nya litcrata, 

 G. v-scripta, Pectcn fibrosns, Opis corallina, Natica clio, Nerinaa 

 Goodhalli (sometimes upwards of a foot in length), Chcmnitzia 

 Hcddingtonensis, Plcurotomaria Mihistcri, and Phasiandla striata. Sea- 

 Urchins are abundant, they include Cidaris flori gemma, Echinobrissiis 

 {Nucleolites') scutatus, Pygaster umbrella, Hernicidaris ijitermcdia, Acrosa- 

 lenia decorata, and Pseudodiadema versipora. Other fossils are the 

 Annelides Serpida intestinalis, and S. tricarittata ; the Crustacean 

 Glyphea rostrata ; Fishes, Asteracanthus, Gyrodiis, etc., and Saurians, 

 Megalosaurus, etc. 



The more detailed divisions of the Corallian Beds of Yorkshire, 

 as noted by Mr. W. H. Hudleston, are as follows :' — 



i Upper calcareous grit ("Red rock") flanking the 

 western part of the Vale of Pickerinc;, 

 Kirkby Moorside, Hdmsley. 

 Argillo-calcareous beds (cement-stone or ' Throst- 

 ler') of the Vale of Pickering. 

 Argillo-calcareous beds (Cement stones) of the 

 Howardian Hills. 

 ! Rag of Scarborough district, Cayton, Brompton, etc. 

 Cidaris-Jtoiigenima-i-xg of the Vale of Pickering, 

 and Langton Wold, Helmsley. 

 Hildenley limestone and North Grimston limestone. 



^ P. Geol. Assoc, iv. 359, v. 410 ; G. Mag. 1880, p. 246 ; 18S2, p. 146 ; see 

 also Q. J. xxxiii. 315, and Phillips, Geol. Yorkshire, part I. 



