240 GEOLOGY OF THE ISLE OF WIGHT. 



and the two nearly coincident anticlinal axes of the Isle of Wight, 

 run nearly east and west. The want of parallelism in these great 

 folds is not sufficient, however, to invalidate the assumption that 

 they form part of a single series, and were formed contem- 

 poraneously. 



They have, moreover, this property in common, namely, that 

 the north side of every anticline is much steeper th.an the 

 south side. Thus the strata rise gently towards the north for a 

 varying distance, and then, reaching the crest of the fold, plunge 

 suddenly down, slowly to rise again. This sudden downward 

 plunge is seen in the Hog's Back, in Portsdown, and in the central 

 Downs of the Isle of Wight, which form the northern sides of 

 the respective anticlinal folds, enumerated above. 



We may next notice that these folds do not run for an indefinite 

 distance either east or west, but die away, each syncline being 

 truly an elongated basin, and each anticline an elongated dome. 

 The two ends of a fold are visible in one instance only, viz., in the 

 anticline of the Weald, but the western terminations of all the 

 others, excepting the Isle of Wight (Brixton) anticline, can be 

 seen, and in this case we find the eastern termination of the fold 

 near the centre of the Island. The Sandown anticline, which 

 commences where the Brixton anticline dies away, probably itself 

 disappears a shitrt distance east of Sandown ; for, as previously 

 pointed out, the strike of the Chalk in the southern Downs is such 

 as to cause this range to meet the central range at an oblique 

 ano-le. Similarly we have evidence of the eastern termination of 

 the Isle of Wight syncline off Selsea Bill, 



In respect of their relative positions to one another these folds 

 show this peculiarity, that while they run east and west (approxi- 

 mately), as if formed by a force acting from the south, they are 

 arranged en echelon along a line running a little north of east. 

 This can be most easily rendered intelligible by drawing a 

 line through the whole system of folds touching the area of 

 maximum movement in each fold. Such a line starting from 

 near Weymouth, runs between Cowes and Newport, near Ports- 

 down and Chichester, a little north of Battle, and thence out into 

 the German Ocean, where presumably the deepest part of the 

 London syncline is situated. The line thus traced has a direction 

 of east 10^-15° north, and, what is deserving of remark, is not 

 very far from being parallel to the great Chalk escarpment across 

 England. 



The Palaeozoic Rocks on which the Secondary strata rest in 

 the north-west (»f France, and which doubtless pass under the 

 south-east of England are known to be intensely contorted, and 

 thrust over one another, the strike of the folds being about west- 

 north-west, turning to east and west where they emerge at the 

 surface in Devon and Somerset, The Carboniferous Rocks of 

 Valenciennes also tend to assume this strike towards the west. 

 But though there is this approximate agreement in direction 

 between the folding of the Secondary and Tertiary Rocks, and 

 that of the Palseozoic Rocks, it must not be concluded that any 



