§15. 



THE ISLE OF PORTLAND. 



383 



chalk to the oolite inclusive, being exposed along this 

 coast, within a distance of five miles.* The subjoined 

 diagram {Lign. 82) will explain the geological structure of 

 these bays. 



Lign. 82. — Plan of the coves on the south-west coast of the 

 Isle of Purbeck. 



a, Chalk. 



b, Firestone, c, Gait, d, Greensand. 

 /, Purbeck beds, g, Portland stone. 



e, Wealden. 



The northern barrier of the coves consists of precipitous 

 chalk cliffs ; the entrance is formed by rocks of Portland 

 and Purbeck limestone ; and between them is a low tract 

 composed of the less durable wealden strata. These bays 

 expose, in fact, transverse sections of the range of hills 

 formed by the Portland and Purbeck beds ; and of the 

 clays, sands, &c. of the Wealden ; and, at their back, pre- 

 cipices of great height, produced by the destruction of the 

 southern face of the vertical chalk of the Downs. 



Thus, within the distance of six or seven hundred yards, 

 we may examine the entire series of strata, from the Chalk 

 to the Portland oolite, by proceeding from the inland cliffs 

 to the southern extremity of the bays ; the section of the 

 east side of Lulworth Cove {Lign. 83) shows the relative 

 position of the formations. 



lo. The Isle of Portland. — The island, or peninsula, 

 of Portland, is a bold headland, off 'Weymouth, about 

 four miles and a half in length, two in breadth, and 



* Geol. Exc. Isle of Wight, p. 368—389. 



