24 Mr. Hopkins on the Structure of the 



positive evidence of facts is not great. The point at which the river at Dorking 

 breaks through the chalk escarpment is directly opposite the extremity of Leith 

 Hill, which has obviously been a point of considerable disturbance, and it is highly 

 probable that any transverse fracture there might also pass through the chalk. 

 Near Seven Oaks, I have already shown that a well-defined line of fracture in the 

 greensand would, if produced, pass along the river-course through the chalk. The 

 course of the Arun through the chalk is along the direction of the valley by which 

 it cuts through the greensand, and which affords direct evidence of dislocation. 

 The course of the Ouse at Lewes seems also evidently connected with the great 

 disturbance which has there taken place. But one of the best indications perhaps 

 of the connexion between transverse valleys and dislocation in the chalk is afforded 

 by the well-marked valley along which the road from Godstone to London passes. 

 The state of internal dislocation of the chalk is shown by the occasional bursting 

 forth of a copious stream which takes its course northward down the valley. This 

 does not occur, I believe, more than once in two or three years, and after a more 

 than usually rainy period. I am told that the water possesses some property which 

 renders it very destructive to vegetation. 



Another case also, though not comprised within the district with which I am 

 immediately occupied, deserves notice. I allude to the transverse course of the 

 river Medina through the middle of the central ridge of the Isle of Wight. The 

 two parts of the ridge on the east and west respectively of the north and south 

 transverse valley are not in the same line, but are so situated that their anticlinal 

 lines are parallel and about two miles apart. The western portion of the ridge 

 swells out to the north on the west of the cross valley to meet the extremity of the 

 other portion, the dip of this connecting portion of the range being generally about 

 north-west and south-east, or in some parts more easterly and westerly. The an- 

 nexed diagram represents an east and west section of the valley of the Medina 

 near Rookley, and very nearly in the direction of the more southerly anticlinal line. 

 It presents a north and south line of flexure which must almost necessarily be ac- 



1 



4. Chalk. 



3. Upper Greensand. 



2. Gault. 



1. Lower Greensand. 



companied by a corresponding north and south fracture, in which I conceive the 

 valley to have originated. 



