IN THE ISLE OF PORTLAND AND AROUND WEYMOUTH. 53 



occupies two thirds of the spire when viewed mouth upwards : suture 

 deep : mouth more round than oval, effuse at the base : outer Up 

 thin : inner lip reflected ; behind it is a small but distinct umbilical 

 chink. 



L. 0-075 ; B. 0-05 inch. 



Its nearest ally is B. parva, var. interrupta, from which, as well 

 as from the other varieties of that common species, the present differs 

 in its cylindrical shape, bluntly pointed spire, and the absence of 

 coloured markings. It somewhat resembles a dwarf Hydrobia 

 Ferussina. 



EXPLANATION OP PLATE I. 



Pig. 1. Outline section from Portland to Dorchester, showing the outline of 

 the anticlinal. True scale. 



2. The same section from Portland Bill to Dorchester. Horizontal scale 



1 inch to 1 mile ; vertical scale 1 inch to 1000 feet. 



3. Bestored section on the same line before the elevation of the anticlinal. 



Scale as in fig. 2. 



4. Section of the Eaised Beach at Portland Bill, west side. True scale. 



5. Section of Old Angular Land-debris at Chesilton. True scale. 



6. Map of Portland Bill and the adjacent parts of Dorsetshire. Scale 



% inch to 1 mile. 



Discussion. 



Eev. O. Fisher remarked on the polished pebbles exhibited, from 

 the summit of the Isle of Portland. Tusk of Elephant and remains of 

 Bos longifrons, with a sling-stone, were found on a ledge in a fissure, 

 which was blocked at one end by a talus of fine materials from the 

 surface, with land shells. The polish on the pebbles was produced 

 by water containing mud filtering through them, and passing below 

 into a fissure caused by the slipping of the stone on the clay. 



Mr. Topley considered that the disturbance described was of com- 

 paratively recent date ; but he was scarcely prepared to admit that 

 it was as low down in the Drift Period as the author supposed. 



Prof. Hughes thought that the whole question turned upon the 

 original configuration of the country — what was the line of the old 

 channel in the old river-valley now forming the English Channel. 



Prof. Ramsay remarked that many questions were raised by this 

 paper. In the anticlinal of the Weald the Cretaceous strata are 

 accidentally conformable, whilst more to the west the Oolites are 

 unconformable to the Cretaceous. The mass of the Eocene passed 

 over the anticlinals of the Portland district ; and what had become 

 of the overlying mass? He thought that it had probably been 

 removed by subaerial influences. 



Mr. Koch referred to the polishing of stones in river-beds, which 

 he had noticed in the north of Spain, in Bohemia, and in the Jura, 

 and stated that in river-beds carbonate of lime is deposited on the 

 stones and preserves their polish. 



Mr. Godwin- Austen said that to whatever period the east and 



