3 o8 



[Proc. B.N.F.C, 



Portlandian series is typically represented in the Isle of Portland, 

 where the economic value of the building-stone series has been 

 known for two centuries. The great beds of calcareous oolitic 

 freestone composing this series dip at a high angle to the north, 

 along the coast between Lulworth and Durlstone Head, and form 

 a barrier against the assaults of the waves. Where, however, they 

 have become breached the softer Purbeckian and Cretaceous rocks 

 above and behind soon become eaten backward, and thus we get 

 beautiful inlets and coves. The celebrated Purbeck marble is 

 obtained from the Purbeckian series between Durlstone Head and 

 Swanage. The finest scenery on the coast is to be seen east of 

 Weymouth, and extending to and beyond St. Alban's Head. 

 Here we have in some places great mural cliffs of chalk and 

 greensand, and in others highly-tilted and contorted beds of 

 the Portland and Purbeck rocks. Many of the cliffs seen in the 

 horns of the excavated coves give complete sections of the whole 

 series. A great anticlinal fold originating in Weymouth Bay and 

 running to the Isle of Wight, together with the great Purbeck fault 

 and overthrust, which runs inland from Lulworth to Ballard 

 Head, north of Swanage, were the prime factors in bringing about 

 the present disposition of the denuded strata of the area. The 

 lecturer concluded a detailed reference to Portland Isle by a 

 description of the Chesil Bank. This is a huge pebble bank or 

 beach of enormous cross-sectional dimensions, and connecting 

 Portland Isle with the mainland beyond Abotsbury, eleven miles 

 away, and running thence to Bridport as a beach for nine 

 miles more. The material of which it is composed is derived 

 mainly from the rocks, sedimentary and igneous, that occur to 

 the westward as far as the Land's End. 



At the conclusion of the lecture some very interesting lantern 

 slides were thrown upon the screen. These included, in addition to 

 fine views of the beautiful scenery of the district, a comprehensive 

 series of maps and sections, the details of which were clearly 

 explained by the lecturer, and added much to the geological 



