118 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 13, 



These facts are offered as additional evidence in support of the 

 conclusion I put forward in a communication on the area of the 

 English Channel, — viz. that a very large portion of it formed a con- 

 tinuous surface of dry land with the adjoining parts of France and 

 England, at the time of the Large Mammalian fauna in these coun- 

 tries. The geological phaenomena of this age are in perfect harmony 

 on either side of the Channel. 



It may have been remarked by whoever has sailed along the French 

 coast at the distance of a few miles, that the chalk-cliffs rise to a very 

 uniform elevation along their whole course : they have the appear- 

 ance of a vertical wall rising from the sea, with openings at intervals, 

 where deep valleys open out at the sea-level ; whilst at times such 

 depressions in the outline only extend downwards for a portion of the 

 height of the cliffs. The valley-systems of this chalk -area are some- 

 what remarkable ; they take their rise at the very summit-level, 

 descend rapidly, join others, and finally merge into one of the great 

 lines of drainage : small streams flow down some, only occasional 

 streams down others. They are all valleys of excavation ; but in no 

 instance has this process gone lower than, or so low as the sea- level, 

 except perhaps in the estuary parts of one or two of the larger rivers. 

 As we cannot imagine that the depths of these valleys can have had 

 any influence in determining the amount of the general elevation of 

 the chalk-formation over this area, the contrary may be assumed, — 

 viz. that the amount of elevation has determined the extent of ex- 

 cavation. 



Over the whole of the chalk-area here described, the upper tabular 

 surfaces are covered with the accumulation of flint-drift, not in con- 

 fused masses, but in alternating layers of clay, coarse detritus, and 

 sands, with diagonal bedding, and all other indications of successive 

 accumulation. The materials of the gravel occur in the valleys, but 

 under totally different appearances. They here present no regularity 

 in arrangement, conform to the slopes, and are mixed up with the 

 subaerial accumulations of the hill-sides, which they seem to have 

 incorporated with them. As a general rule, the heights are covered 

 with gravel, and the valleys are free. 



It follows then that the valley-systems must have been mainly 

 formed since the dispersion of the Drift ; — and this is confirmed by the 

 fact that it is only in the deeper valleys before mentioned, such as 

 those of the Somme, the Authie, and the Canche, — which are valleys 

 connected with the axis of Artois, — that old terrestrial surfaces occur 

 which were coeval with the extinct fauna of large mammals. 



From this we may venture on one further inference, — that the agent 

 which has produced the greater part of the existing valley-systems of 

 the chalk-area of the North of France has been merely meteoric. 

 Against this any denudation-theory is inadmissible, in consequence 

 both of the irregularly diverging character of the valleys, and the 

 loose materials on the summit-levels. Had these deep narrow valleys 

 existed prior to the Drift, they must necessarily have been filled before 

 any accumulation could form and be spread out uniformly over the 

 higher levels. 



