PART 11. CHAPTER XVII. 



213 



Divisions of the Oolite. 



CHAPTER XVII. 



OOLITE AND LIAS. 



Subdivisions of the Oolitic group — Fossil shells — Corals in the calcareous divi- 

 sions only — Buried forest of Encrinites in Bradford clay — Changes in organic 

 life during accumulation of Oolites — Characteristic fossils — Signs of neighbour- 

 ing land and shoals — Supposed cetacea in Oolite — Oolite of Yorkshire and Scot- 

 land. 



Oolite. — Below the freshwater group last described, or, 

 where this is wanting, immediately beneath the Cretaceous for- 

 mation, a great series of marine strata, commonly called " the 

 Oolite," occurs in many parts of Europe. This group has been 

 so named, because, in England and other places where it was 

 first examined, the limestones belonging to it had an oolitic 

 structure. (See p. 27.) These rocks occupy in England a zone 

 which is nearly thirty miles in average breadth, and extends 

 across the island, from Yorkshire on the north-east, to Dorset- 

 shire on the south-west.* Their mineral characters are not uni- 

 form throughout this region ; but the following are the names 

 of the principal subdivisions observed in the central and south- 

 eastern parts of England : — 



OOLITE. 

 jT i a. Portland stone and sand. 

 ( b. Kimmeridge clay. 



Middle ^-g°i-t^. 



( e. Cornbrash and Forest Marble. 

 Lower < f. Great Oolite and base of Fullers' earth. 



(J g. Inferior Oolite. 

 The Lias then succeeds to the Inferior Oolite. 



The upper oolitic system of the above Table has usually the 

 Kimmeridge clay for its base, and the middle oolitic system the 

 Oxford *clay. The lower system reposes on the Lias, an argillo- 

 calcareous formation, which some include in the lower oolite, but 

 which will be treated of separately in the next chapter. Many 

 of these subdivisions are distinguished by peculiar organic 



* For details respecting this formation in England, see Conybeare and Phil- 

 lips's Geology, chap. iii. 



