244 Dr. PiTTON on the Strata beloiv the Chalk. 



ward as a valley surmounted on both sides by hills. It will be seen from 

 the Map, Plate IX., that the anticlinal line by which this lower tract is tra- 

 versed coincides in direction with that of the great Wealden denudation of 

 Hants, Surrey, and Sussex; and is parallel also to the line of upthrow on 

 the coast of Dorsetshire and the Isle of Wight, and to other shorter lines 

 of elevation, the connexion of which is not at present visible, on the north of 

 the Weald, — through Burgh-Clerc, Ham, Shalbourne, and Burbage, to 

 the Vale of Pewsy. One of the anticlinal lines of the lower strata, beneath 

 the new red sandstone, from Frome to the Steep Holm in the Bristol Channel 

 also runs nearly from east to west ; whilst, on the contrary, another line of 

 fault by which the lower beds are intersected, beginning near Portishead- 

 point on the west of Bristol, runs northward, across the Severn, through 

 Newnham, and thence to the north-west of Gloucester *. 



(126.) The Vale of Wardour has the general form of a triangle, the base 

 of which extends from the chalk hills on the south of Shaftesbury to those of 

 Mere, the apex being a little to the west of Harnham Hill on the south-east 

 of Salisbury : for it is deserving of observation, that the stream of the Nadder 

 escapes from this valley, not directly through the angle at its geological sum- 

 mit, but through the north side; in a manner perfectly analogous to that of 

 the egress of the streams from the Wealden denudation in Kent and Sussex. 



The heights which bound the vale consist at top of chalk, the incHnation 

 of which, like that of the strata beneath it, on the north of the anticlinal 

 line, is in many cases more than 20°; while on the south, it is seldom more 

 than 3° or 4°, apparently deviating but little from the general disposition of 

 the strata in the South-east of England ; and this anticlinal line itself is 

 throughout much nearer to the north than to the south side of the vale. 

 The strata from the chalk down to the gault inclusive seem to be continued 

 all through, and to be nearly uniform in thickness ; but the surface between 

 the chalk hills is very irregular, and is divided by a ridge or bar formed 

 by the escarpment of the Portland strata, on the east of which the ground 

 is hilly, but on the west comparatively flat and low : — the appearances being 

 altogether such as would arise from the deposition of the green-sands and 

 chalk, over a tract partially occupied by the Purbeck and Portland forma- 



* The anticlinal lines near Bristol, on the Map, Plate IX., are taken from Messrs. Buckland 

 and Conybeare's paper on that district. For a full account of their relations to those in the South- 

 east of England, the reader is referred to a paper since published by the Rev. W. Conybeare 

 (London and Edinburgh Phil. Mag. for 1832, vol. i. p. 122, &c.), who states that one of the great 

 lines of fault, by which the transition strata of the Quantock Hills in Somersetshire (beyond the 

 range of the Map, Plate IX.,) are traversed, runs also nearly east and west. 



