﻿PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Nov. 7, 



of the land. Sea-waves cannot excavate long narrow inlets in ho- 

 mogeneous beds (such as Chalk), nor in horizontal beds, such as the 

 gravel and clay of the district under notice ; for the effect of sea- 

 waves is to form long and approximately straight lines of cliff. Any 

 curvature seen in such a line of cliff will be found to be due to some 

 disturbing cause, as a variation in the resisting power of the strata, 

 or the set of a current, or exposure of some parts to a greater force 

 of wind, in which cases a bay will be formed, but not a long and 

 winding creek. 



If it were possible (which the author denied) for such valleys as 

 those of the district under consideration to be formed by wave- 

 action, their sides should present the appearances of degraded cliffs, 

 masked with a talus of gravel derived from their crests ; instead of 

 which, their sides are rounded, the gravel-beds thinning out at the 

 hill-top, and the clay exposed on the sides ; nor is there any evidence 

 of the existence of shingle-beds at the foot of the hills. 



The only other agency of an ordinary character to which such 

 denudation could be attributed seems to be tidal action, either at a 

 time when the district was under water, or else during a gradual 

 rise. But it seems impossible that the diurnal slow passage of a 

 body of water to and fro over a sea-bottom could sweep out diverging 

 narrow channels, carrying clean away gravel charged with large 

 pebbles. Nor does the second supposition seem more favourable for 

 the purpose, because the rapidity of the current in the tidal portions 

 of the rivers, as we see them, is not competent to do more than to 

 keep clear a comparatively narrow channel in their centres, the sides 

 becoming covered with a deposit of mud (dry at low water), which, 

 in the upper portions, forms alluvial tracts of meadow-land ; nor does 

 there seem any reason why the denuding power of the tidal rivers, 

 during a gradual rise, shoidd be greater than at present. 



Mr. Fisher does not see any other way of accounting for such a 

 form of surface as obtains in this district, and in many others com- 

 posed of yielding strata, than by a superincumbent mass of water 

 rapidly draining off from a fiat or slightly dome-shaped area. Slight 

 depressions, cracks, or hues of readily yielding materials would first 

 determine the course of the streams of drainage ; and these would 

 cut channels which would be more or less completely scoured out 

 according to the velocity of the water. Where the gravel-covering 

 of such a district was cut through, the clay beneath would be chan- 

 nelled with a narrower and deeper valley, — the cutting power of the 

 water being also assisted by the gravel hurried along with it ; and 

 where the gravel was wholly removed, the valleys would be wider, 

 and the intermediate high ground rounded instead of being flat- 

 topped. This character of surface is seen in the most eastern portion 

 of Essex, and in nearly all clay-districts which are not low and flat. 



The surface of the mud of a tidal river left dry at low water shows, 

 on a small scale, a configuration identical with that described, and 

 clearly due to the draining off of the superincumbent water when 

 the tide falls. The only difference in the mode of action is that, in 

 this case, sediment, instead of being swept away, after having been 



