the Purbeck and Wealden Deposits of England and France. 273 



similar lines intersecting the axis of the Isle of Wight, but 

 whose points of intersection are hidden from us by the water of 

 the British Channel. 



The drainage through Essex and Suffolk possesses a direction 

 imparted to it by valleys which have rolled off, as it were, from 

 the axis of the Weald upheaval, or been scooped out along lines 

 of fracture connected with that upheaval. The valley of the 

 Thames from Barking to Gravesend, which, after an interruption 

 between that place and Chatham, is continued behind the Isle of 

 Sheppey, departs but little from the line of the chalk escarpment 

 between Folkestone and Maidstone. The valley of the next river 

 northward (the Crouch) is parallel with the Weald axis \ but the 

 other rivers of Essex successively as we go northwards, the Chel- 

 mer, Blackwater, Colchester, Colne, and Stour, curve in the 

 upper part of their courses towards the north, the convexity of 

 the curve, like that of the Pas de Calais trough, being towards 

 the south-west. The rivers of East Suffolk (the Orwell, Deben, 

 and Aide) preserve this direction throughout their courses. 

 The valleys, which in South Essex are parallel with the Weald, 

 lose, like the rivers, that parallelism towards the north of the 

 county ; and the cretaceous and tertiary deposits in like manner 

 change, although obscurely, the direction of their strike into one 

 more and more oblique to the Weald axis, until in West Norfolk 

 the strike of the lower chalk is north and south, changing this di- 

 rectiontowards the east gradually,so that inEast Norfolkthe strike 

 of the upper beds becomes N.W. to S.E., like that of the river- 

 valleys of East Suffolk. On the other hand, at the extreme west of 

 Norfolk the strike of the lower cretaceous and oolitic formations 

 inclines from the north and south line in the opposite direction, 

 viz. from N. by E.to S. byW., and towards that of the old Jurassic 

 strike in this particular region — the Great Ouse following up to 

 Shefford in Bedfordshire the Jurassic strike along the line of what 

 I am about presently to refer to as the north-east opening of the 

 mesozoic gulf, while the Waveney from Diss to the sea not 

 improbably follows the outline of the north-western shore of the 

 palaeozoic barrier. I associate this gradual curving of the strike 

 with the existence of the palaeozoic barrier beneath it, and infer 

 that the latter has made its presence felt in the counties of Essex 

 and Suffolk by modifying the upthrow of the beds overlying it 

 at the time of the Weald upheaval, not less than it has in East- 

 ern Kent and Sussex, and in the portion of France opposite to 

 those counties, by resisting the pressure of the less indurated 

 beds of mesozoic origin there abutting up to it, and which in 

 the upthrow were forced against it. 



The conclusion at which Mr. Hull* has from other conside- 

 * Quart. Journ. Geol. Soc. vol. xvi. p. 66. 



Phil Mag. S. 4. Vol. 25. No. 168. April 1863. T 



