THK .lUlASSir SYSTKM I \~> 



aii'l Imven ha\v been recognised. The lower (from 80 to 90 feet) 

 contains Canli"<-> /".- ttlternans, Astarte supracorallina, Ostrea 

 tl'ltoidea, etc. ; the upper, of which only 16 feet is seen, contains 

 H.i-Di/i/rK cirgula and Orbiculoidea latissima, but still higher beds 

 may be concealed beneath the Cretaceous rock-. 



In Lincolnshire both lower and upper divisions are well de- 

 veloped, and the whole stage is probably about 600 feet thick. The 

 lower l>cds arc exposed near Horncastle, Wragby, Market Rasen, 

 and Wiawliy near Caistor. At Rasen they yield many finely 

 preserved fossils which include Cardioceras alternant, P,erisphinctes 

 mutabilis, Trigonia Juddiana, Inoceramus rasenensis, Thracia 

 depressa, and Nucula Menkei. The upper beds are mainly shales, 

 seen near Spilsby, Fulletby, and West Ash by, and yielding Per. 

 oiplex, Protocardia striatula, Lucina minuscula, Lingula ovalis, and 

 Orbiculuidea latissima. 



In Yorkshire the Kimeridge Clay is not well exposed, for 

 though it doubtless underlies a large part of the Vale of Pickering, 

 it is concealed by Glacial drifts, and only the highest beds are 

 exposed on the shore at Speeton Gap. These consist of brown and 

 black shales containing Perisphinctes biplex (?), Ostrea gibbosa, 

 Discina latissima, and Lingula ovalis. 



4. The Portland Beds or Portlandian. Like the 

 Kimeridge Clay, these beds are thickest in Dorset and thin north- 

 wards. They are well exposed between Durlstone Head and St 

 Alban's Head (see Fig. 149), where they are divisible as follows : 



Feet. 



Upper Portlandian (Freestone Beds . . . 40 to 50 



zone of Hole, giyanteus \ Cherty Beds . . . 60 to 75 



Lower Portlandian ( Sandy marls, sands, and calcareous 

 zone of Perisph. yigas \ sandstone ..... 130 to 160 



230 to 285 



The hard sandy marls of the lower group contain Perisphinctes 

 biplex, Exogyra bruntutana, Trigonia incurva, Tr. Pellati, and Rhyn- 

 chonella portlandica. The "cherty beds " are brown earthy limestone 

 with irregular layers and nodules of flinty chert ; Pecten lamellosus 

 and Protocardia dissimilis occur in these beds. The freestones are 

 oolitic liuit-tiiiif-, which are largely quarried for building stone; 

 they contain Trigonia gibbosa, Perna mytiloides, Cerithium port- 

 landicutn, and Holcostephanus giganteus. 



At Portland the succession is similar and the total tliirkm 

 about 220 feet, but at Upwey, north of Weyinouth, a different 

 facies presents itself, the whole Upper Portlandian having passed 

 into a white chalky limestone with black and grey flints. This 



