The Rev. W. Buckland on the Excavation of Valleys, ^c. 97 



It is not easy to imagine how valleys of this last description could have been 

 formed in any conceivable dumtion of years by the rivers that now flow 

 through them^ since all the component streams^ and consequently the rivers 

 themselves which are made up of their agg-regate^ owe their existence to the 

 prior existence of the valleys through which they flow. 



Of the same nature with those last described are the valleys which intersect 

 the coast of Dorset and Devon. In passing along this coast (see the Map and 

 ViewSj Plates XIII. and XIV.) we cross, nearly at right angles, a continual 

 succession of hills and valleySj the southern extremities of which are abruptly 

 terminated by the sea, the valleys gradually sloping into it, and the hills being 

 abruptly truncated, and often overhanging the beach or undercliff, with a 

 perpendicular precipice. The main direction of the greater number of these 

 valleys is from north to south; that is, nearly in the direction of the dip of the 

 strata in \vhicli they are excavated : the streams and rivers that flow through 

 them are short and inconsiderable, and incompetent, even when flooded, to 

 move any thing more weighty than mud and sand. 



The greater number of these valleys, and of the hills that bound them, are 

 within the limits of the north and north-west escarpment of the green sand 

 formation ; and in their continuation southward they cut down into the oolite, 

 lias, or red marl, according as this or that formation constitutes the substratum 

 over which the green sand originally extended. There is usually an exact 

 correspondence in the structure of the hills inclosing each valley; so that, 

 whatever stratum is found on one side, the same is discoverable on the other 

 side upon the prolongation of its plane : whenever there is a want of corre- 

 spondence in the strata on the opposite sides of a valley, it is referable to a 

 change in the substrata upon which the excavating waters had to exert their 

 force. 



The section of the hills in this district usually presents an insulated cap of 

 chalk, or a bed of angular and unrofled chalk-flints, reposing on a broader bed 

 of green sand ; and this again rests on a still broader base of oolite, lias, or 

 red marl (see Plates XIII. and XIV.). With the exception of the very local 

 depression of the chalk and subjacent green sand and red marl on the west of 

 the Axe, at Beer Cliffs, the position of the strata is regular and very slightly 

 inclined ; nor have any subterraneous disturbances operated to an important 

 degree to affect the form of the valleys. 



If we examine the valleys that fall into the bay of Charmouth from Burton 

 on the east to Exmouth on the west, viz. that of the Bredy, the Brit, the Char, 

 the Axe, the Sid, and the Otter, we shall find them all to be valleys of diluvian 

 excavation ; their flanks are similarly constructed of parallel and respectively 



VOL. VI o 



