Ixii. MARINE GEOLOGICAL EXCURSION. 



north-west side of the anticlinal in the cliffs between Hobarrow and Brandy 

 Bays. 



Gadcliff, Worbarrow Say, and Rings Hill (Floivcrsbarroiv). These features 

 terminate the Isle of Purbeck on its west coast. Gadcliff (482ft.) presents a fine 

 escarpment facing the south, with beds dipping into the hill at an angle of 30 P . 

 The basal slopes consist of Kimmeridge Clay, passing into Portland Sands, whilst 

 the precipice consists of Portland Eock just capped by Lower Purbeck. There is 

 a fine development of Middle Purbeck at Pondfield Hole, where also the junction 

 between Purbecks and Portlands may be well studied. Worbarrow Tout marks 

 the extremity of the Purbeck series in the Isle of Purbeck itself ; here the beds 

 dip 40 N. The dips of the Wealden Beds in Worbarrow Bay range from 18 

 near the Coastguard Station to 30 under Eings Hill. The width of the Wealden 

 outcrop here is about half-a-mile, as against 1m. 3f. in Swanage Bay. In 

 Mupe Bay, about 2 miles westward, the outcrop is still smaller, and in Lulworth 

 Cove smaller still. Hence the bays of Swanage, Worbarrow, Mupe, and Lulworth 

 diminish in size in proportion to the areas of the Wealden, in which they have 

 been excavated. Eings Hill (567ft.) consists of Chalk with a base of Greensand. 

 The ancient British camp on its summit, known as Flowersbarrow, has been 

 partially destroyed by the slipping of the cliff, and thus serves to mark the 

 amount of coast erosion since those days. 



Arish Mell and Mupe Say. Owing to the destruction of the rampart of 

 Oolitic rocks, which should stretch from Worbarrow Tout to the Mupe Eocks, a 

 distance of nearly two miles, the sea has once more reached the Chalk, and we 

 perceive the picturesque inlet of Arish Mell with nearly vertical cliffs on either 

 side. This is the commencement of the peculiar scenery of Lulworth ; dips of 75 

 in the Chalk on both sides. Cockpit Head, on the west, is conspicuous even on 

 this wonderful coast. The view of Lulworth Castle through Arish Mell Gap is 

 noteworthy. The wall of Oolitic rocks once more protects the coast from Mupe 

 Bay to Lulworth Cove, and here there is a complete section from Portland Beds to 

 Wealden. 



Lulworth Cove and Stair Hole. It is probable that the party will land here 

 and perhaps inspect the famous " Fossil Forest." Here, if convenient, the Director, 

 might make a few remarks on the objects of the excursion. Note the effect of 

 earth -stresses (mountain making) in the contortions of the rocks the Upper 

 Purbeck folded and the Lower Wealden inverted. The basal bed of the White 

 Chalk (zone of Rhynchonella Cuvieri) forms the head of Lulworth Cove, whilst the 

 entrance is guarded by stout Portlandian rocks. The so-called "Fossil Forest " 

 is a dirt bed, or old soil cap, on which rest the stumps of coniferous trees with 

 their roots imbedded in the soil, whilst the trunks have been broken off at a 

 height of about 3ft. Both stumps and trees have been enveloped in domes of 

 tufa, presenting curious forms. The sigmoidal curvature of the Purbeck Beds at 

 Stair Hole is also noticeable. 



Dungy Head, Durdle Door, Bat's Head, etc. The wall of Oolitic rocks is 

 intact at Dungy Head, and forms a strong buttress against the inroads of the sea. 



