45 8 Drawing by Arthur Severn, 



Clifton, through which the Avon passes, is due to the ground having been 

 perforated. 6 I believe the steepness of the cliff at Box Hill, 75 at the south-east 

 corner, is due to the ancient cave, through which the waves passed, originally 

 being at that point ; and that the under-cutting below enabled the chalk cliff 

 to be nearly as steep as at the sea shores, where the water has undercut, as at 

 Culver Cliffs. This is the case of the nearly vertical cliffs at Cheddar ; for 

 when there was a tunnel, the roof falling in, left a vertical cliff above. There 

 must have been very high ground at Bristol. 



In a period with twenty to fifty times as much rain as at present, these 

 underground passages for rivers would be formed with great facility, there 

 being the assistance of 80 or 100 ft. head of water. We have the evidence 

 from the pipes in the chalk, that this water was heavily charged with carbonic 

 acid gas, although we do not know the source. Under such circumstances the 

 Gorge of Brading would be easily made. 



At West Knighton, two miles W. from Brading, an opening was being formed 

 when the wet period ceased. You can see on the model the deep grooves being 

 cut out by water. Every coombe is due to springs, and long escarpments, 

 such as the Surrey Hills, or the escarpment of the Lias and Oolite, called the 

 Cotteswold Hills, were being prepared for boring in this manner. 



Figs. 27 and 28 represent what has happened at Brading. 



Fig. 29A represents a limestone valley, Dove Dale, where the sides are veiy 

 steep, owing to the greater stability of the carboniferous limestone than the sands 

 (Fig. 29). The undercutting, by the river, nearly occupying the position of an old 

 underground channel, is clearly shown. If Mr. Jukes had considered the method 

 I have shown of the formation of gorges, when describing the Irish rivers 

 Shannon and Blackwater, &c, I think he could have explained the causes of 



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FORFC/fOU/VO WFMOEH BEDS ft A NO K A, SEVERN- DEI. 



their present direction more satisfactorily. His paper on rivers laid the founda- 

 tion for the subsequent papers on the same subject by Prof. Ramsay. 



The forms of valleys, lakes, and waterfalls affect and are affected by this 

 special degree of motion of the water or ice, which modifies their forms, or causes 

 what in mechanics is called instability. Indeed, valleys and escarpments with 

 their springs, are integral parts of every complete river system. The earth and 

 the water flowing over it must be considered at the same time, so intimately are 

 they connected. They are related almost like the veins to the blood, and the 



sap vessels to the sap in a tree. - ^__ 



5 See note, page 472. 



