Report of an Excursion to Hindhead

88 REPORT OF AN EXCURSION TO HINDHEAD. SATURDAY, JULY 4TH, 1914. By DOUGLAS LEIGHTON, F.G.S., Director of the Excursion. THE object of this excursion was to study the character of the lower portion of the Lower Greensand, as developed in the western end of the Wealden area, and to discuss some of the complicated physical problems of Hindhead and the neighbour ing hills. Arriving at Witley Station at 11.45 the party proceeded by footpath to Sandhills. The Director first pointed out the Lower Greensand escarpment, which here does not rise above 470 ft. above O.D., and which runs almost due east and west for a few miles between Hascombe and the eastern side of Hindhead. At Hindhead the outcrop turns suddenly south, and the escarpment rises to almost 900 ft. above O.D. This change is due partly to the alteration in the dip of the beds and partly to the increased thickness of the chert beds, which at Witley are only poorly developed, while at Hindhead they reach their maximum known thickness. The general character of the beds of the whole district is much the same as that of the Leith Hill area, the variations being only such as would be expected from the conditions under which the Lower Greensand was deposited. At Sandhills a pit in the Lower Sands was visited. The Director emphasised the fact that these Lower Sands which immediately overlie the Atherfield Clay are probably always present, though frequently obscured by the scree from the rubbly cherts above. Where, however, the cherts are poorly developed, as at the spot on which the party stood, a strip of easily recognisable sand land is found. At the top of the low escarpment massive sandstone and poor chert were seen in the roadside and in an old quarry. The party then proceeded down towards Brook Street, a similar section of chert and sandstone overlying Lower Sands being seen in the lane side. At Brook Street a large pit in the Atherfield Clay was visited. The top portion of the pit showed a light, sandy clay, which could probably be classed as Passage Loams (Gregory)," these being the passage beds between the Lower Sands and the clay below. In the lower part of the pit, some what sanely clay was seen with the usual calcareous nodules. The nodules are, as a rule, fossiliferous, but although a thorough search was made, only one specimen, a small species of Exogyra, was found. From here the party walked across the Weald Clay to Bound- * Proc, Geot. Assoc. vol. xiv, p. 120. DOUGLAS LEIGHTON, EXCURSION TO HINDHEAD. 89 less Farm. It was pointed out that, whereas the top of the Atherfield Clay at Brook Street stood at about 340 ft. above O.D., here on the eastern slope of Hindhead it was met with at an elevation of530 ft. above O.D. Climbing up through the woods, Gibbet Hill, the highest portion of Hindhead, was reached, and owing to the beautiful clearness of the atmosphere, the members were fortunate enough to obtain as fine a view over the surround ing country as it is ever possible to have. As previously pointed out, the elevation 0' Hindhead is due to the height to which the Lower Greensand beds have been raised, the structure being somewhat in the nature of a dome. The hill is cut offfrom Blackdown,which lies immediateiyto the south by the deep Haslemere valley. This valley coincides with a syncline, and this has probably determined the course of the branch of the Wey which runs in it. The most striking feature of Hindhead however is the deep combe of the Devil's Punch Bowl. The steep sides come up to a level ridge which runs all round the head without a break, except for some notches on the east side, just north of Gibbet Hill. A narrow tongue of Atherfield Clay is ex posed in the bottom of the valley, and it was suggested that the cornbe was a grand example of spring erosion. The original stream wherever it entered the valley, and at a much higher level, had gradually lost its water supply, owing to the working back of the escarpment, till finally when the Atherfield Clay was tapped, the chief source of supply was the spring thrown out by the clay. The spring gradually worked its way back, clearing away the material that would fall down from all sides till eventually the grand combe as seen now would be formed. After discussing this and other problems, the party proceeded to the Post Office for tea. Afterwards, on the way down to Haslemere, the opportunity was taken to study the chert beds. The Atherfield Clay crops out in the Devil's Punch Bowl at 616 ft. above O.D., and the top of Gibbet Hill being 895 ft. above O.D. it means that after allowing for a thickness of Lower Sands, nowhere seen here owing to the scree, there must be at least 200 ft. of chert beds. There are only 100 ft. of these beds at Leith Hill (965 ft. above O.D.), and these two facts go to show that the chert beds, though an important factor, are not nearly so important in regulating the general height of the escarpment as the height to which the beds have been raised by movements. The return to London was made from Haslemere Station. Mr. E. C. Martin acted as Excursion Secretary. REFERENCES. Geological Survey Maps, Sheet 8 (Old Series). Ordnance Survev. r inch, Sheet I2S. rS7S. TOPLEY,·W.-" Geology 01 the W ..ald." Mem. Ceo!. Suroey, r894. FOWLER. BINSTFAD.-" The Hythe Beds in the Liphook and Hind head District." Proc, Geo/, Assoc., vol. xiii, p. 3')I..

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