﻿1851.] 



AUSTEN ON THE PLEISTOCENE PERIOD. 



119 



rocks of the coast-line yield to the action of the sea, and on the di- 

 mensions which one component portion has acquired. 



The sections taken about the point of land forming the west side 

 of Falmouth harbour, and at low water, give an outline such as is repre- 

 sented by Section No. 4. PI. VI. A similar condition of coast is 

 shown in fig. 1 . 



The lowest zone (a) is that of the thick growth of Fucus, the upper 

 limit of which presents a true horizontal line, and which may be taken, 

 as suggested by M. Bravais (Voyages en Scandinavie, &c, p. 67), as 

 that of the mean sea-level. 



The zone next above this (b) presents a clean surface of rock, with- 

 out marine vegetation, and its uppermost limit is that of the maximum 

 rise of the tide. At the spot where the section fig. 1 is taken, there 

 is no beach even at low water ; the materials of the sea-bed are found 

 only as patches of sand, shingle, and broken shells filling the hollows 

 and inequalities of these zones : these two zones form the tidal belt 

 of the present sea-level. 



§ 1. Higher than this last, there is again another very distinct 

 zone (c) presenting a rugged surface of rock, overgrown with grey and 

 orange lichens, and having the hollows filled with tufts and masses 

 of grasses, Armeria, Plantago, Erythrsea, &c, rooted in sea-sand. 

 This zone extends upwards to the base of the cliff (<?) ; it is now wholly 

 and permanently beyond the reach of the sea, and is the upper tidal 

 zone of a former level, when the sea reached and formed the cliff at 

 (e) ; it indicates a change of level, which so far as elevation is con- 

 cerned, is necessarily the most recent which has taken place on this 

 section, and which we may estimate at 8-10 feet. 



The horizontal breadth of this zone (c) from place to place, de- 

 pends on the form of the outline of the sea-margin between tides, 

 when the land stood at the former level : often, as at the west of the 

 entrance to the harbour of Dartmouth, see fig. 1, the outline is nearly 

 that of a platform : in these cases there is often such a thick growth 

 of vegetation as to conceal the features above described : the evidence 

 of its origin as a true marginal sea-zone is to be found by the removal 

 of the surface turf, when the loose sea-sand with rolled and broken 

 shells will be usually found beneath. 



I have selected Falmouth and Dartmouth, as they are places of 

 easier access than most others ; because the evidence is to be clearly 

 seen there ; and because the amount of vertical rise, which is the 

 same at both places, can be easily determined. 



About the coasts of the whole of the group of the Channel Islands 

 there are sections which are the exact counterparts of the foregoing, 

 and where, owing to a rise of small amount, the sea does not now 

 reach a line which clearly marks its former level (see fig. 2) . 



The features above described, illustrative of the latest alteration of 

 the sea-level, belong to places situated on the open coast ; and to this 

 period of the lower level of the land, I would refer such accumulations as 

 those of the valley of the Exe (Geol. Trans, vol. vi. p. 440), inasmuch 

 as a depression of from 8-10 feet would convert the whole of that area, 

 as high as Exeter, into a salt-water estuary, and account for the beds 



