﻿1851.] 



AUSTEN ON THE PLEISTOCENE PERIOD. 



125 



the operations now in progress are limited to the conveyance of ma- 

 terials in the minutest state of subdivision, and imply only the condi- 

 tions of slow atmospheric decomposition : no accession of fragmentary 

 beds takes place now, nor has been made for some long time past. 

 Such a condition, however, gradually shows itself, as we trace down- 

 wards the superficial accumulations of the interior of those districts 

 whose coasts we have described ; such as those of the West of England, 

 the Channel Islands, and the Cotentin : we everywhere may observe a 

 passage downwards into beds which mark a time when the degrada- 

 tion of the surface proceeded much more rapidly than by the mere 

 effects of decomposition, and when fragments of rock, and even blocks 

 of large dimensions in certain localities, far exceeding the moving 

 power of any rain-fall, were conveyed down the very slopes along 

 which the minutest particles of matter only are now carried. 



That the general surface accumulations of the West of England, 

 the Channel Islands, and of the main land of the Cotentin, are of the 

 same age, for their lower and principal portions, with those which 

 in each of those districts are found overlying the older sea-beds, is 

 clearly to be ascertained by tracing them away from such positions, 

 up valleys which open out seawards, and so into the interior. In the 

 coast section west of Falmouth, we see the beds in question resting on 

 marine strata up to a given level, but when the outline of the country 

 rises above such level, the beds of angular materials are still carried 

 on, and rest on the fundamental slate rocks. 



I have already noticed the local character of these accumulations, 

 and also that in no instance over the large area where they occur, do 

 they ever contain any water-worn fragments, or any which might not 

 reach their present positions if only detached from some mass above : 

 the thickness of the beds of detritus depends directly on the elevation 

 of the ground with which they are connected, as also does their frag- 

 mentary character, and the dimensions of the blocks. In the Falmouth 

 coast sections may be seen an instance, but which will occur to any 

 observer in many other places, which serves to throw some light on 

 the nature of the agencies engaged in producing these accumulations : 

 here, at a place where the outline presents so small a slope that great 

 power would be required to remove any coarse materials, we have on 

 the surface of the rock a thick mass of angular fragments, and in this, 

 the subordinate portions of the subjacent strata, such as the sandstone 

 beds and quartz veins, are represented by strings of such materials 

 running disconnectedly in lines through it. In this and like cases we 

 have the effects of powerful mechanical disintegration, whilst the re- 

 sults of the process have remained in situ. 



The white clays in the parish of St. Agnes, those of Trewidnek near 

 St. Ives, 20 feet beneath the surface, as also those of Lenant and 

 Madern, near Penzance, would seem to belong to the sub-aerial accu- 

 mulations, from the evidence of the section of the strata of St. Agnes 

 Beacon. The uppermost layer of rounded shingle would in this case 

 belong to the upper high sea level (d) here described. The elevation 

 of St. Agnes, upwards of 450 feet, would show the very unequal cha- 

 racter of the movement of the land proceeding westwards. 



