VIII. — On the Excavation of Valleys by diluvian Action, as illustrated 

 by a succession of Valleys which intersect the South Coast of Dorset 

 and Devon. 



By the Rev. WILLIAM BUCKLAND, f.r.s. f.l s. v.p.g.s. 



AND PROFESSOR OF GEOLOGY AND MINERALOGY IN THE UNIVERSITY OF OXFORD. 



[Read April 19, 1822.] 



JVIY intention in the following communication is to consider the general 

 causes to which valleys owe their origin, and particularly such as occur in 

 horizontal and undisturbed strata within the limits of their escarpments. That 

 portion of the coast of Dorset and Devon which lies on the east of Lyme and 

 on the east of Sidmouth, affords some of the best examples of such valleys with 

 which I am acquainted : I beg therefore to present to the Society two geo- 

 logical views of that coast, drawn at my request some years since by Hubert 

 Cornish, Esq., which will tend also further to illustrate the description given 

 of it in a preceding paper by Mr. De la Beche. 



Many valleys may be ascribed to the elevation or depression of the strata 

 composing the adjacent hills, by forces acting at very remote periods from 

 within the body of the earth itself; and to similar forces we may principally 

 refer the high inclination and contortions of strata that occur in the highest 

 mountains, and sometimes also in minor hills : other valleys have been occa- 

 sioned by the strata having been originally deposited at irregular levels, and 

 others by some partial slip or dislocation of portions of the strata. 



But at different periods of time intermediate between the deposition of the 

 most ancient and the most recent formations, the irregularities of level arising 

 from the preceding causes have been variously modified by the action of vio- 

 lent inundations hollowing out portions of the surface and removing the frag- 

 ments to a distance : to such circumstances we must ascribe the water-worn 

 pebbles of the old red sandstone, the red marl, and the plastic clay formations. 



A cause similar to that last mentioned has wrought extensive changes on the 

 surface (however variously modified by preceding catastrophes) at a period 



