392 



GEOLOGY OF THE SOUTH EAST OF DORSETSHIRE. 



them to their junction with the plastic clay at the point C on 



the map, is given in the following figure, (45). 



45 



Chalk Cliffs from Old Harry to the Plastic Clay. South side of Studland Bay 



The chalk is, as before mentioned, through a great part of 

 the space, nearly horizontal ; but it has a gentle dip to the 

 north-west, which increases as it approaches the plastic clay, 

 near which it has suffered local derangements. The cliffs 

 are of a medium softness, but are easily separated into quad- 

 rangular or trapezoidal blocks, and, where horizontally bed- 

 ded, are fissured by vertical cracks from top to bottom. They 

 are also spotted, like the Suffolk chalk, with manganese, and 

 contain much yellow matter, probably decomposed pyrites. 

 It is by the instrumentality of these cracks, that the perpen- 

 dicular buttresses before spoken of occur on either side of the 

 promontory at Old Harry (vol. ii. p. 131) ; and thus the cliffs 

 on the south side of Studland Bay, have been separated into 

 divisions by the action of the sea. As there is nothing mate- 

 rial between Old Harry Point and the division nearest to the 

 plastic clay, I have introduced the profile from the point E of fig. 

 45, as a sufficient illustration of the whole of the phenomena. 

 It will be seen by the examination of that diagram (fig. 46), 



Profile view of Studland cliffs from the point E to Old Harry. 



A, Old Harry Point. C c, vertical crack down the cliff. Distance from C to D, 49 paces. 



Distance from D to E 28 paces. 



that the measure of the decay of the cliffs is, to a certain de- 

 gree, regulated by these vertical fissures : the line C c in fig. 

 46 shows this very clearly, for it is impossible that the pro- 



