The Rev. W. Buckland on the Excavation of Valleys, ^c. 101 



that it probably formed a continuous or nearly continuous stratum, from its 

 present termination in Dorsetshire, to Haldon on the west of Exeter *. 



From the correspondence observed by Mr. Wm. Phillips between the strata 

 of Dover and on the hills west of Calais f, and by Mr. De la Beche between 

 the strata of the coast of Dorset and Devon, and those of Normandy +, it may 

 be inferred (after making- due allowance for the possible influence of those 

 earlier causes, which in many instances have occasioned valleys) that the 

 English Channel is a submarine valley, which owes its origin in a great mea- 

 sure to diluvian excavation, the opposite sides having as much correspondence 

 as those of any valleys on the land. Mr. De la Beche, as I am informed, has 

 already drawn the same inference from his own observations. According- to 

 Bouache, the depth of the straits of Dover is on an average less than 180 

 feet; and from thence westward to the chops of the channel the water gradu- 

 ally deepens to only 420 feet, a depth less than that of the majority of inland 

 valleys which terminate in the bay of Charmouth ; and as ordinary valleys 

 usually increase in depth from the sides towards their centre, so also the sub- 

 marine valley of the channel is deepest in the middle, and becomes more shal- 

 low towards either shore. 



It seems probable that a large portion of the matter dislodged from the val- 

 leys of which we have been speaking by the diluvian waters that hollowed 

 them out, has been drifted into the principal valley, the bed of the sea ; and 

 being subsequently carried eastward by the superior force of the flowing 

 above that of the ebbing tide, and partially stopped in its further progress 

 by the Isle of Portland, has formed that vast bed of pebbles known by 

 the name of the Chesil Bank : the principal ingredients of this bank are 

 rolled chalk flints and pebbles of chert ; the softer materials that filled the val- 

 leys, such as chalk, sand, clay, and marl, having been floated off" and drifted 

 far into the ocean, by the violence of the diluvian waters. 



* There is also reason to think that the plastic clay formation was nearly coextensive with the 

 chalk ; for on the central summits of Blackdown there are rounded pebbles of chalk flint, which 

 resemble those found in the gravel beds of the plastic clay formation at Blackheath : and on the 

 hills that encircle Sidmouth there are large blocks of a siliceous breccia, composed of chalk flints 

 united by a strong siliceous cement, and difiering from the Hertfordshire pudding-stone only in 

 the circumstance of the imbedded flints being mostly angular, instead of rounded as in the stone 

 of Hertfordshire : a Tariation which occurs in similar blocks of the same formation at Portisham, 

 near Abbotsbury, and elsewhere. — The argument, however, arising from the presence of these 

 blocks and pebbles is imperfect ; as it is possible, though not probable, they may have been 

 drifted to their actual place by the diluvian waters, before the excavation of the valleys. 



t See Geological Transactions, Vol. v, pp. 47, Sec. + See p. 89 of the present volume. 



