GEOLOQY. 177 



precipitous, and on the other, the clays and chalk too easily 

 acted upon by the atmosphere and sea, lose all traces of their 

 ancient forms excepting in a few spots where circumstances have 

 favoured their preservation. In Purbeck, Gad-cliff has evidently 

 been subject to the action of the waves during a gradual emer- 

 gence or upheaval : sea-worn caverns occur almost at its summit. 

 The western side of Kimmeridge bay is another instance of a 

 change which has taken place at a comparatively recent period, 

 where limpets, winkles, &c., are abundantly distributed. At 

 one period of the history of this coast, these moUusks appear to 

 have been the principal proprietors of the district. The common 

 periwinkle and mussel are foimd on our raised beaches in the 

 boulder clays and mammaliferous crags, and as far back as 

 the red crag: but the common edible cockle and pecten, (C. 

 e., and P. o.,) occur, not only in these successive beds, but 

 in the coral crag also. Wherever cockles are met with they 

 aboxmd. As is well known, their habitat is a sandy bed, which 

 the violence of the sea may and does frequently break up. On 

 tlie Paignton sands near Torquay, I witnessed such a catastrophe ; 

 tlie unfortunate moUusks lying helplessly on the shore, were 

 raked up and conveyed away as manure by the neighboiuing 

 agricultui'ists: a tide would convey many of them to a favourable 

 position for entombment in a bed then in course of formation. 



Hunter, in the Geological Journal, speaking of the Devon 

 coast says, that the movement which effected the elevation was 

 cither gentle, or that a great area had been simultaneously 

 raised en masse j so that the present position is due to an eleva- 

 tion, and not to a depression of the level of the sea. 



Mr. Austen says, at p. 126, "Mi\ Mansel suggests that the 

 land shells might have been picked up by the sea, &c;" "still, 

 if we grant this to be possible, they would be discovered not 

 only in one isolated spot, but frequently over tlie whole district, 

 &c." I have the authority of Mr. Wilcox, an eminent naturalist 

 and observer of nature, that such a deposit as the one at Blash- 

 enwell has been met with in the neighbourhood of Swanage, by 

 workmen who were digging a well some time since, and I have 

 no doubt that others may eventually be discovered after further 

 investigation. 



