Excursion to Betchworth and Headley
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124 EXCURSION TO BETCHWORTH AND HEADLEY. REFERENCES. G.eo!ogical Survey Map, Sheet 8 (Drift Ed ition). SIx-Inch Ordnance Survey Map, Surrey, Sheet 32. 1865. ME;':ER, C. J. A.-" On the Lower Greensand of Godalming."-Ceo!. Assoc. 1875. TaPLEY, W.-"The Geology of the Weald." Mem. Geo). Survey. 1894. GREGORY, J. W.-" Excursion to Guildford and Shalford.' Proc, Geol. Assoc., vol. xiii. 1895. LEIGHTON, T.-" The Lower Greensand above the Atherfield Clay of East Surrey," Quart. Yourn. Geol. Soc., vol. li, EXCURSION TO BETCHWORTH AND HEADLEY. SATURDAY, 18TH MAY, 1895. Directors :-H. W. MONCKTON, F.L.S., F.G.S., and W. P. D. STEBBING, F. G.S. (Report by the DIRECTORS.) The party assembled at Cannon Street Station, and travelled by the 1.35 p.m, train to Betchworth Station on the South Eastern Railway. On arrival the party ascended the chalk downs, and walked across Headley Heath to Headley Church, which stands on one of a group of Eocene outliers on the chalk,as is shown in the diagrammatic section (p, 125). On the north side of the outlier, Mr. Stebbing pointed out a: small exposure in the Thanet Sand in a sand pit, and at a rather higher level at the roadside he had discovered the oyster bed of the Woolwich and Reading Series. Specimens of the oysters Ostrea Bellovadna-were obtained by such of the party as cared for them. The oyster bed is overlain by mottled clay, and according to Prof. Prestwich,* there is a thick pebble bed at the top of the hill. This is no doubt in what is now Nower Wood, and clearly the pebbles which are very abundant in the gravel at Tot Hill, are derived from it. The party next proceeded to a sand and gravel pit at Tot Hill, where Mr. Monckton made the following remarks: "The height of the group of Eocene outliers at Headley is 600 feet above the sea-that is rather more than 100 feet below the crest of the North Downs at this part of their range, the Betch worth Hills and Colley Hill, above Reigate, being 700 feet above sea-level. The occurrence of Eocene beds at this low level is partly due to the fact that the strata here dip to the north, and consequently the outliers rest on the dip slope of the chalk; but I am inclined to think that they also rest very unconform ably on it, an unconformity not due to original unconformable deposition, but to the subsequent subterranean decay of the chalk • Q.art.lourn. Ceol. Soc., vol, x (,854), p. 97. JULY, 1895.] EXCURSION TO BETCHWORTH AND HEADLEY. 12.5 126 EXCURSION TO BETCHWORTH AND HEADLEY. by which the Eocene strata have been let down;" and I believe that they now lie on the chalk in the irregular manner which I have indicated on the diagrammatic section in the programme where the unconformity is much exaggerated. "The Eocene outliers consist of Thanet Sand and Reading Beds, and a vast interval must have elapsed between their deposition and that of the next formation at this place. The next deposits are the sand bed A with the gravel B which overlies it, and they like the Eocene beds have in places been much disturbed by the decay of the chalk beneath them. This is more especially the case at Tot Hill, where a mass of the gravel B may be seen resting against the sand A instead of lying on top of it, and the sand A extends nearly to the bottom of a little side valley in the chalk far below the level of the Eocene outlier-a position in which I do not believe it was originally deposited. In places it looks as if the strata had sunk down into a very large swallow-hole,t and I think this may well have been the case. "On the chalk downs near Chipstead, 4l miles east of Headley, there is a patch of sand very like the bed A of our section, and in 1858 Prof. Prestwich suggested that it might be of the same age as the Lenham Beds.j' and it is therefore possible that the sand A of Headley--the patch of sand at Chipstead, and also one at Netley Heath-may belong to the early Pliocene.§ In any case I feel sure that they are more recent than the Eocene Period. " Though the gravel B has in places been subject to slipping and letting down, it forms as a whole a fairly flat plain, the highest part of which is some 630 feet above the sea. The gravel consists mainly of flints from the chalk-often large, as much as a foot in length-sometimes hardly at all water-worn, but usually a good deal rolled. There is also a large proportion of flint pebbles from the Eocene Beds and some chert and ironstone from the Lower Greensand. " The presence of this last ingredient in fair abundance shows that the gravel is derived from the south, and as it is now bounded on the south by the clay-with-flints C, which runs along the crest of the downs, the gravel B must be older than at least the greater part of the clay-with-flints C. Next, a bed of loam or brick-earth D rests on the clay-with-fiints, and finally the gravel of the River Mole E is obviously newer than the beds A, B, C, D. We have thus established the order of succession of the beds shown in the section in the programme." After an examination of the pits the party proceeded to • Compare Topley, Geol. o/the TVeald('87.')' p. 230, Fig. 45. t Evidence of this was pointed out on the spot. : Quart./ourn. Geot. Soc., vol. xiv (,858), p. 33', note. § See Whitaker, Mem. Geot. SU1'l1ey, vol, iv (,872 ), p. 339. EXCURSION TO BETCHWORTH AND HEADLEY. 127 Heath House, where Mr. and Mrs. Stebbing entertained them at tea. Afterwards a collection of Chalk fossils from Betchworth, belonging to Mr. W. P. D. Stebbing, was inspected, and the party again crossed Headley Heath to Pebble Coombe, near which are some workings in clay-with-flints, which were in spected, and Mr. Monckton continued his remarks as follows: " It will have been observed as we crossed Headley Heath that, in spite of subterranean erosion and decay, the gravel B is in places fairly flat, and where similar gravel rests upon non calcareous beds, as in the case of the hills round Aldershot, for example, the flatness of the surface is very marked. "These flat expanses of gravel do not, however, only occur at the tops of hills-e-thete are plenty of examples at all sorts of levels down to the gravel-covered flats on both sides of the Thames, near London, which are but little elevated above the sea. "Upper Hale, Aldershot, is one of the highest of these gravel flats in this part of England, being 600 feet above the sea, and it is noticeable that, in places, it has what seems to be the remains of a covering of brick-earth, just as is the case with the low-level Thames gravels. "Now I am quite unable to conceive any method by which all these gravel-flats, ranging from sea-level to 600 feet above, could have been deposited simultaneously-neither the sea, nor a lake, nor rivers, nor a flood, nor ice, could at one and the same time, have laid down these gravels where we now find them. " Clearly long periods must have elapsed between the deposition of the different sheets of gravel. "If, however, we accept Prof. Prestwich's view that some of the gravels I have mentioned, and which he includes in his Southern Drift, are pre-glacial in age, and if, as I think is clear, we have a continuous succession down to the lowest gravels of the Thames Valley, then we need feel no trouble as to length of time-the Glacial Period is long enough for us. " After a careful consideration of the views of various authors and a lengthy examination of the gravels themselves, I have adopted the opinion that the gravels of these flats have been formed by river action-s-of course assisted by ice and snow during the glacial period. My views on this point will be found in the Quarterly Journal of the Geological Society for 1892,'*' and I am pleased to find myself on the same side as Mr. Hudleston, at any rate as regards the hill or plateau gravels.f- "In 1892 Mr. Clement Reid brought forward a new theory as to the origin of the Thames Valley gravels.j contending that they • Quart. ]ourn. Geol. Soc., vol. xlviii (1892), p, 45. f Quart. f ourn, Geol. Soc., vol. xlix (1893), Proc., p. 76. t Quart. ]ourn. Geoi, Soc., vol. xlviii (1892), p, 360. 128 EXCURSION TO BETCHWORTH AND HEADLEY. are not river-gravels, but frozen-soil gravels laid down on plains sloping gently to the River Thames. This view seems to suppose that the Thames Valley was formed witbout gravels, and that the gravels then' as one sheet' 'belonging to a single period' were introduced. It is scarcely fair, however, to criticise this theory, as it has not yet been worked out by the author in detail, but perhaps I may say that though I think it possible, and even probable, that there are frozen-soil gravels in the Thames Valley, I think at the same time that the greater part of the gravels are true river-gravels, though no doubt their formation was largely due to glacial conditions.