468 Geology of the South-East of Dorsetshire. 



enrring as portions of horizontal strata, which seems to be 

 the chief point to be proved, but which is not proved satis- 

 factorily, either by Mr. Webster or by the authors of the 

 Outlines. It also accounts for a fact I have observed, that 

 the strata near the fault are thinner than at a distance, as well 

 as harder. 



That the chalk and plastic clay series have, en masse, under- 

 gone a vertical elevation, and that the line of elevatory force 

 was in the line of fault assumed, may be shown by examina- 

 tion of the highly inclined and deranged beds of the plastic 

 clay, between Poole and Christchurch, and at Studland, as 

 well as by the other phenomena alluded to at the commence- 

 ment of this paper; for the lines of fault now forming the 

 joints at Ballard Head have their direction analogous to 

 those cracks of which mention has been made; and it would 

 be unphilosophical to suppose that the chalk could under 

 the effect of a general law, which has operated over so 

 extensive an area under precisely similar circumstances, 

 affecting, also, so many different rocks, have exhibited a dis- 

 location exclusively eccentric. 



That the edges of the southern portions of the fractured 

 chalk beds would necessarily be upheaved, there are nume- 

 rous examples to prove, in formations of wide geological 

 distance from the chalk : but one instance may be quoted 

 from that very range of chalk in the Isle of Wight, of which 

 the Purbeck Hills are a continuation, and which we give in 

 the following section {fig. 52.), taken from Mr. Webster, 



Hastings sand. Green Chalk. Plastic 



sand. clay. 



Section across Sandown Bay, Isle of Wight. 



1, Sandown Bay. 2, Culver Cliff. 3, Bembridge Down. 4, White CliffBay. 



where the edges of the beds above the plastic clay are seen 

 turned up, exactly as the curved chalk beds are in the case 

 before us. 



The dislocation and fissures in Purbeck, on both sides of 

 the chalk, conform to the general law, and mutually illustrate 

 it and the joints and faults at Ballard Down. Thus, the 

 deep fissure in the Purbeck beds, leading to Tilly Whim, if 

 prolonged, passes through the crack in the chalk at Corfe 

 Castle; perpendicular to which line is the junction of Durl- 

 stone Head, Peveril Point, Ballard Plead, Old Harry, and 

 the Chine at Bourne Mouth, on the Hampshire side of Poole. 



Thus, again, the deep fissure which leads from Renscombe 



