C— GEOLOGY. 77 



along which the Vale of Pewsey, Vale of Warminster, and the Vale of 

 Wardour have been eroded. At the western end of the Weald the folds 

 pitch in general to the westward, while in the above-mentioned vales the 

 pitch is eastward. A change of pitch takes place somewhere in the middle 

 of the chalk plateau between Salisbury Plain and the western end of the 

 Weald. Just as the folding apjsears to gain in intensity and definition 

 as one goes from the western end towards the centre of the Weald, so if 

 the movement were continued westward beyond the Cretaceous outcrop 

 its effects might be expected to become prominent again in the next region 

 of dome culmination somewhere to the west. 



Despite the fact that the Middle and Upper Jurassic outcrops appear 

 to be almost devoid of folding transverse to their outcrops, there is a 

 remarkable general correspondence between the main folds that traverse 

 the base of the Cretaceous and those that affect the base of the Lias farther 

 west. 



The upfold of the Cretaceous rocks in the Vale of Pewsey, which may 

 be regarded as the westerly prolongation in a modified form of the Guildford 

 Hogback and the Kingsclere monocline, can in fact be traced in the Jurassic 

 rocks ; the axis of the upfold swings in a west-south-westerly direction 

 towards Frome. Beyond that place it is prolonged in the anticlinal region 

 of the Mendips, and the north-westerly trend of the Mendip fold west of 

 Frome is, as it were, a mirror image of the north-easterly trend of the 

 fold east of that place. The fold is partly replaced by a strike fault which 

 partakes in the swing of the anticlinal axis. 



The Vale of Warminster upfold is less obvious ; it can be recognised, 

 however, in the Jurassic rocks round Wanstrow, but it cannot be traced 

 into the base of the Lias south of Shepton Mallet, unless it is replaced 

 by a strike-fault which runs through the Jurassic outcrops nearly parallel 

 with the Mendip fold. The marked anticlinal axis accompanied by a 

 strike-fault, which traverses the Vale of Wardour, produces little apparent 

 effect in the Middle Jurassic rocks, but in the continuation of the line to 

 the west a strong upfold of the Lias is indicated by the strike lines of the 

 base of the formation which swing in an east-uorth-easterly direction from 

 south of Taunton to Somerton, and thence in a westerly direction to the 

 south shore of the Bristol Channel at Watchet and Porlock. The same 

 fold is obvious also in the trend of the Middle and Upper Lias from 

 Ilminster, through Yeovil, Castle Cary and Glastonbury. 



These correspondences can hardly be accidental, and it is my belief 

 that the folding revealed by the differences of level in the base of the Lias 

 indicates the continuation into the Bristol Channel region of the Miocene 

 folds that traverse the south-east of England. 



It is of interest also to consider the correspondences between the 

 synclines of the Bristol Channel region and those farther east. One of 

 these is immediately obvious. The extension of the Cretaceous rocks far 

 to the westward of the main trend of the outcrop into the Blackdown 

 Hills south of Wellington undoubtedly indicates a prolongation of the 

 Hampshire basin. It may be observed that the Jurassic rocks exhibit a 

 similar though less pronounced deviation to the westward. 



The syncline that intervenes between the upfolds of the Vale of 

 Wardour and the Vale of Warminster corresponds in position and direction 



