GEOGRAPHY OF THE STRATA. 361 



septaria, and bands of sandy concretions ; beds 

 of lignite, and highly bituminous shales and clays; 

 marine shells are very numerous ; total thick- 

 ness, 800 feet. One species of oyster, the Ostrea 

 deltoidea, is characteristic of this group, and occurs 

 abundantly in every locality.* 



Geographical distribution of the strata. — 

 The White chalk forms a narrow but lofty chain of 

 hills, that ranges inland across the Island, from 

 Handfast Point (section, lign. 28), to the cliff 

 called Bats-corner, on the south-western shore. 

 The lower cretaceous deposits appear along the 

 southern escarpment of the downs ; the chalk is 

 also exposed to the east of Bats-corner, in Wor- 

 barrow, or Worthbarrow Bay, and in several 

 lesser bays or coves, that have been excavated, by 

 the long-continued action of the waves, in the 

 Purbeck and Wealden deposits, that form the 

 southern cliffs. The height of this chain of 

 downs is from 500 to between 600 and 700 feet. 

 Ballard Hill, over Handfast Point, is 584 feet, 

 and Ninebarrow Down, 642 feet high. A line of 

 chalk cliffs forms the coast from Bats-corner to 

 Whitenore (see lign. 36), where the cretaceous 



♦ Sowerby's " Mineral Conchology " contains figures of many of the shells 

 of the Portland Oolite ; and in Dr. Fitton's Memoir, plates xxii. and xxiii., 

 several species are figured and described. 



