Evans — On Cavities in Old River Gravel. 445 



which, however, with the exception of a small opening in it, was 

 left entirely undisturbed. On hearing of this discovery I immedi- 

 ately arranged to go down and examine into the phenomena, and 

 accordingly, on the 8th of July, Mr, Flower, Mr. Fitch, and I met 

 upon the spot. We found a face of gravel and sand exposed, about 

 24 feet in height from the chalk at its base to the superficial soil 

 at the summit. The upper part of the section showed sand with a 

 few gravelly seams, about eight or ten feet in thickness ; at the base 

 of this occurred a dark band of ferruginous argillaceous sand a few 

 inches in thickness, then some eight or nine feet of ochreous gravel, 

 with a red sandy matrix, which was separated by a band of grey 

 sand from the lower beds of gravel which contained a very large 

 percentage af rolled Chalk and seams of chalky sand. 



The opening into the cavity was not much more than a foot in 

 diameter, and was about the middle of the bed of ochreous gravel. 

 It was soon sufficiently enlarged to enable one of us to creep in, and 

 by the aid of a candle to examine the cavity. It was slightly 

 irregular in form, and seemed about three feet in diameter and about 

 five feet in height, but we did not take any accurate measurements, 

 as we were in constant fear, and not without reason, of the face of 

 the cliff of gravel falling in upon us. The bottom of the cavity had 

 some sand upon it, which had fallen from the roof, the cavity extend- 

 ing upwards through the gravel, so that its ceiling was formed by the 

 base of the sands above. The axis of the cavity was not quite per- 

 pendicular. Having examined it as far as was consistent with safety, 

 we next commenced cutting a vertical groove in the face of the gravel 

 below, with a view of ascertaining whether, as I had suspected, there 

 was not a sandpipe below, the absorption of the gravel into which 

 was the primary cause of the cavity. The second blow of the pick- 

 axe broke through the wall of gravel and at once revealed a sandpipe, 

 thus proving my view to have been correct. 



We at once proceeded to clear it out as far as was consistent with 

 safety, and found that at about three feet above the base of the gravel 

 the pipe was about two feet in diameter and nearly circular, but 

 whether it descended into the Chalk we were unable to see, and 

 before we left the pit the face of the gravel cliff gave way, and the 

 scene of our operations was buried under a mass many tons in 

 weight. During our examination of the pipe, and while we were 

 speaking of the occurrence of flint implements in these cavities, one 

 of the pointed form was found under our eyes by one of the work- 

 men among the gravel he was clearing out of the pipe. 



The existence of this sandpipe below the cavity, similar in 

 character to the pipes so frequently occurring in sands and gravels 

 overlying calcareous strata, at once proved that these cavities were 

 of natural and not of artificial origin. As, however, such cavities 

 are of extremely rare occurrence, and have not, I believe, been 

 previously noticed except by Mr. Fitch, who did not enter into the 

 question of their origin, it will be well to devote a short time to a 

 consideration of the causes to which they are due. 



Mr. Prestwich was, I think, the first to point out that such pipes 



