THE RIDGWAY FAULT. 65 



few words about the anticlinal axis which lies before us between 

 the chalk escarpment and the sea, and which is in reality one of 

 the most important and instructive geological features of the whole 

 district. This axis passes from Weymouth Bay to the Chesil 

 Beach, and produces an arch-like disposition of the group of strata 

 composing the valley or low ground in front of us. Forming the 

 central line of this axis is the Forest marble, bearing on its 

 shoulders the Cornbrash, the Oxford Clay, the Oxford Oolite, 

 Kimmeridge Clay, Portland sand, and Portland stone in ascending 

 order. These, under the influence of denudation, have been 

 planed down, exposing the Forest marble in the centre ; therefore, 

 in traversing the district in a south-west and north-east line from 

 Portland Bill to Kidgway Hill, we find the strata repeat themselves 

 on either side of this axis with wonderful regularity, complicated 

 slightly, I admit, in one or two points by the occurrence of one or 

 two faults near the northern outcrop of the Cornbrash. The forces 

 producing this important anticlinal axis acted in a line continuous 

 with that extending through Purbeck and the Isle of Wight, and 

 parallel to the great axis of the Weald of Kent and Sussex. The 

 question presents itself When did these elevations take place, so 

 important in the configuration and landscape of the south of 

 England ? It appears, taking cognisance of all facts, that these 

 lines of elevation were produced subsequent to the deposition of 

 the London clay, if not, indeed, as there seems every reason to 

 believe, subsequently to the deposition of the newest Tertiaries of 

 the Isle of Wight. 



Another axis of elevation in the south-west of England presents 

 itself to our minds that of the Mendip Hills, in Somersetshire, 

 which, running east and west, cuts that county, as it were, into two 

 halves, and this axis is parallel to our own of Ridgway. The 

 Mendip axis has long ago been shewn to be older than the depo- 

 sition of the New Red Sandstone ; but to Messrs. Buckland and 

 de la Beche it suggested a valuable example of M. E. de 

 Beaumont's theory, that lines of elevation on the earth's surface 

 have a strong tendency to run in parallel lines. 



