﻿1851.] AUSTEN ON THE GUILDFORD GRAVEL BEDS. 



283 



level of the canal, or 241 feet above the sea. The angle of slope 

 from the top of the Locknor cutting to the stream, although con- 

 siderable, is not perhaps greater than that on which gravel-beds might 

 accumulate, but the difficulty they here present is this, that along the 

 whole of this section the thickness of the gravel-beds, which has been 

 proved by numerous deep drains, was found not to exceed 4 or 5 

 feet in the lower portion of the valley. The section across the valley 

 at this place, at the time when the gravel-beds were accumulated, 

 could not have presented the same conditions as at present, inasmuch 

 as the thickest beds would have been collected in the deepest portion, 

 whereas we have seen that they occur at what is now the highest ; 

 nor are they ever found to have an elevation on the north side of the 

 valley corresponding to that on the south (see Section, fig. 2). 



I therefore infer that when the gravel-beds were accumulated, the 

 condition of the Tillingbourne Valley was not such as it is now, but 

 that the slope of the beds has been imparted to them since. It will 

 be observed that the gravel-beds end off abruptly at the base of a 

 steep escarpment of the lower greensand (fig. 2) ; and this feature I 

 consider to be due to a fault, the upcast of which being to the north 

 would be attended by a depression on the south, and thus place the 

 gravel-beds as we now find them. 



I had often heard from persons in the occupation of lands along the 

 Tillingbourne Valley, that the surface subjacent to the gravel-beds 

 presented a series of long parallel furrows or troughs, running in the 

 direction of the valley, or east and west ; this was ascertained in 

 draining the land, and it is now found sufficient to cut across these 

 troughs, and thus allow the water they hold to run off. It was only 

 very lately that I had an opportunity of seeing the true character of 

 the surface-outline here described. 



The place at which the Section, fig. 3, is taken is about half a mile 

 west of the position last-noticed (Locknor cutting), and the gravel- 

 beds, instead of dipping north, are separated into two masses by the 

 rise of a ridge of Neocomian clay, d. The southern mass is trough- 

 shaped, the other slopes towards the stream or northerly, in which 

 direction it also thins away. The gravel-beds rise to this ridge on 

 either side : this position might be considered by some as the result 

 of accumulation on an uneven surface. Coarse materials can hardly, 

 however, be supposed to have taken and preserved such steep angles 

 beneath the levelling action of water which had a considerable moving 

 power, for the greatest angle of slope was 46°, and I am therefore 

 inclined to consider that the appearances shown in Section, fig. 3, 

 must be the result of disturbances which have taken place since the 

 first accumulation of the beds. 



The summit of the ridge of Neocomian clay presents a deep fissure 

 filled with gravel (see fig. 3, g). 



I should hardly have been satisfied with the evidence here adduced, 

 as to the comparatively recent date of some of the disturbances of this 

 district, had it not been for the fault (/) which the S. extremity of the 

 Section, fig. 3, presented. This section was taken from a large qua- 

 drangular excavation, made for the offices of a dwelling-house ; the 



