﻿1851.] AUSTEN ON THE GUILDFORD GRAVEL BEDS. 



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floor of the excavation was worked to a true level, with vertical sides, 

 presenting clean sections from 5 to 8 feet deep. The opposite section, 

 or that on the E., corresponded with the one here given as to the 

 composition of the beds of gravel, and their position. The southern 

 end of the section (fig. 3) presented a dislocation (/). It will be seen 

 that there is a downcast to the north and an upcast on the opposite 

 side of the subjacent strata, which here consist of hard Neocomian 

 beds, d. The stratification of the gravel-beds was distinctly marked, 

 and the position of the pebbles in the different layers much disturbed 

 on either side of the fault. As the materials from this excavation 

 were all reserved for various purposes, but from which it was desirable 

 to exclude any clay, the workmen avoided the mass marked d, so 

 that it was left as a ridge or dyke crossing the excavation from E. to 

 W., in which state I first saw it : the section, however, was taken 

 after it had been cut away. The existence of this particular clay- 

 ridge was previously known, from the area of wet land it caused to 

 the south of it ; and whatever may be the case with respect to these 

 clay-ridges at other places, it is clear that this one has been produced 

 by a fault subsequent to the accumulation of the lower gravels. To 

 the south of this spot the gravel-beds increase in thickness, so that 

 at about 30 yards a well there sunk did not pass through them at a 

 depth of 1 5 feet. 



Although I had long since satisfied myself that the accumulations 

 of the age of those here described have been everywhere displaced 

 since their original deposition, yet I should have hesitated, even until 

 recently, as to whether such a statement — as to faults traversing su- 

 perficial gravel-beds — could be made. Such a section as the one here 

 figured is sufficient evidence on this point ; but it is not the only evi- 

 dence which these gravel-beds afford us. Whoever will closely exa- 

 mine any sections of the beds here in question (the one here given, 

 fig. 3, is sufficient), will perceive that there are clear indications of 

 changes of position during the progress of the accumulation. This 

 is a subject respecting which I hope shortly to bring before the So- 

 ciety a considerable mass of evidence taken from an examination of 

 the drift-sands and gravels of the whole of the South of England : for 

 the present it will be sufficient to draw attention to the section here 

 produced, and which is a fair illustration of the phsenomena which 

 constitute the evidence of the case. 



In Section, fig. 3, we may safely assume that the lower beds {a, a) 

 have a higher angle than that at which they were accumulated, or 

 that their present position is the result of some disturbance ; of this 

 the fault (/) is further confirmatory. The portion of the gravel 

 marked (b) is of subsequent date to such disturbance : whilst the 

 upper levelling of the surface implies conditions perfectly distinct 

 from these two antecedent ones. We meet with no indications of in- 

 tervening surfaces of dry land, or other guide by which to estimate 

 the extent of time which may have separated these conditions, but 

 other considerations would render it most unsafe to assume that the 

 disturbances here indicated all took place whilst the area supporting 

 these accumulations of gravel was continuously submerged. 



