352 GEOLOGY OF THE ISLE OF PURBECK. 



Greensand 240 paces. 



Weald clay 46 — 



Hastings sands 3500 — 



Interval between the sand cliffs and the 

 rise of the Purbeck strata 200 — * 



The cliffs in Durlstone Bay are entirely com- 

 posed of the Purbeck strata ; those in the middle 

 are much bent and undulated, but in the southern 

 part, the arrangement of the beds is well displayed. 

 The termination of this coast at Durlstone Head, 

 consists of the marine strata called the Portland 

 oolite, which are seen to emerge from beneath the 

 Purbeck hills (see lign. 28). 



In the coast section thus briefly described we 

 have, therefore, the following series : — 



I. The Cretaceous System, comprising the upper 

 and lower white chalk, firestone, gait, and 

 greensand. 

 II. The Wealden, including the Weald clays, the 

 Hastings beds, and the Purbeck. 

 III. The Oolite, of which the upper, or Portland 

 group, is alone visible. 

 Of these, the Purbeck and Portland strata are 

 for the first time brought under the observation 

 of the reader, and will therefore require more 

 particular notice. 



* Geological Transactions, vol, iv. p. 207. 



