Excursion to the North Downs, Surrey. Monday, 6th May, 1878 - Geologists' Association excursion

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From: A record of excursions made between 1860 and 1890. Edited by Thomas Vincent Holmes , F.G.S. and C. Davies Sherborn, F.G.S. London: Edward Stanford [For the Geologists’ Association], 1891. Source: Cornell University copy on the Internet Archive (Public domain work)
Figure 43 Cavity in the Caterham Gravel Pits. Scale—10 Feet to 1 Inch.
Figure 44 Loam-with-Flints in the Pebble-Beds at Caterham. Scale—10 Feet to 1 Inch.

Note: [On July 13th, 1889, there was an excursion to Limpsfield (Surrey), the Directors being Prof. Prestwich and W. Topley. Gravels yielding palæolithic implements were inspected. See in connection with this excursion, that to Ightham (Kent), June 1st, 1889.]

Directors: Prof. J. Morris, F.G.S., and W. Whitaker, F.R.S.

(Report by W. Whitaker). (Proc. Vol. v. p. 495.)

The party went by train to Caterham, and then walked southwards to the hill on which the Waterworks stand. The outlier of Oldhaven Beds here was examined, and it was shown how the wash of pebbles from this formation down the hill-side, or still more down the gentle northerly slope, obscured the junction with the Chalk, and might easily lead an observer to draw the boundary-line of the Oldhaven Beds too low.

Attention was drawn to the section given by the deep well at the Waterworks, the shaft of which passed through a great thickness of Oldhaven Beds (nearly 90 feet on one side, and 140 on the other); the Chalk was then pierced to the depth of about 455 feet; Upper Greensand, about 55 feet, succeeded, and then Gault, which reached the hitherto unrecorded thickness of over 340 feet; sand (Neocomian) being found below, and the total depth reaching 874 feet.

A large pit just south of the Waterworks showed the nature of the Oldhaven Beds—a deposit of flint pebbles in a sandy matrix, the pebbles all perfectly rolled; but in places, at the bottom, there was seen an irregular mass of angular flints in a loamy matrix; this, it was suggested, might be due to the dissolving away of the Chalk by carbonated water, leaving the insoluble flints behind, which is all the more likely from the fact that the Oldhaven Beds must fill a deep pipe at the Waterworks (as shown by the well-section), and such pipes are produced by the dissolution of chalk below Tertiary and Drift beds [a detailed description of these Gravel Pits, by T. V. Holmes, may be seen in Proc., vol. ix. 1885, p. 105, from which the illustrations are taken.]

An advance having been made to the end of the Chalk escarpment, Prof. Morris gave an address on the connection of the scenery of the district with the geology. Each successive formation (Chalk, Upper Greensand, Gault, Lower Greensand and Weald Clay), was shown to have its own peculiar effect on the surface, the contours of which moreover are greatly affected by the regular northerly dip of the beds.

The Chalk ridge having been descended, two trenches, dug at the foot of "White Hill," by Mr. Gilford, for the benefit of the Members, was examined. The more westerly and higher of these showed the junction of the Chalk and the Upper Greensand, or rather the passage between them; for the Chalk Marl was seen to be somewhat sandy at its base, and to put on the glauconitic character of the " Cambridge Greensand " (which has been shown to be the bottom-bed of the Chalk Marl), until at last it passes into the clayey greensand that in this district forms the top division of the Upper Greensand.

The second trench showed a passage from the Upper Green-sand into the Gault; the lower part of the former, consisting of more or less calcareous sandstone and sand, becoming more clayey towards the base, and merging into the top part of the Gault, which is sandy, somewhat calcareous, and light-coloured.

After lunching with Mr. Gilford, a start was made westward, along the terrace of the Upper Greensand.

Some small sections, showing the nature of the formation, the dip, etc., were noticed, and it was pointed out how the northerly dip, of about 5°, resulted in making the outcrop less winding, that is, less affected by undulations of the ground, than would be the case with more horizontal beds. The lines dividing the Upper Greensand from the Chalk above and from the Gault below were approximately traced (on the " six-inch " Ordnance Map), and it was shown how this could be done from evidence given by the shape of the ground, the character of vegetation, and the occurrence of springs, in the absence of sections.

After a time the party came unexpectedly on a new and hitherto unrecorded section, which alone was worth a visit. It was a road-cutting on the west of Mr. Frith's new house, and continuous from the base of the Chalk Marl to the top of the Gault. The beds shown were as follows, and the section confirmed the conclusions drawn from Mr. Gilford's trenches:

CHALK MARL, full of green grains at the base, and passing down into the next bed.

UPPER GREENSAND. Green sand, partly calcareous.

UPPER GREENSAND. Green and greenish-grey sand, with layers of sandstone; the stone more frequent lower down.

UPPER GREENSAND. Sand, partly calcareous, with layers of stone; lower down more clayey, and the stone-layers lost; passing down into L the next.

Light-coloured sandy clay. Upper part of GAULT.

The walk was continued along the Upper Greensand, the outcrop of which was found to be rather narrower than is shown on the Geological Survey Map (made many years ago, and without the evidence above described). Before reaching Merstham a casual look was given to the large chalk-pit east of the railway, and then the party divided, some returning to London, others walking southward to Redhill, across the outcrop of the Gault to that of the Lower Greensand. The larger number left took train to London, but a band of six continued their southerly stroll up the dip slope of the Lower Greensand to a Fuller's-earth pit close to the top of the escarpment of that formation, and were well rewarded by the sight of a fine section, the beds shown being as below, and all probably belonging to the Sandgate Beds of the Geological Survey:

Brownish clay, in places with broken-up stone at top.

Sandstone, the upper part rubbly, and sometimes soft, the lower part more massive.

Fuller's earth, ironstained at top, the rest bluish-grey.

[On June 14th, 1884, J. Logan Lobley was Director of an excursion to Caterham and Mersthanz, the district traversed being the same as that described in the "Excursion to the North Downs, Surrey." It is reported in Proc., vol. viii. p. 411. Besides seeing various sections of Oldhaven Beds, Chalk, and Upper Greensand, the party also inspected the site of an ancient British camp at Warr Coppice.]

References

Maps

Ordnance Survey. Geological. Sheets 6 and 8. 8s. 6d. each.

New Ordnance Survey. Sheets 270, 286, 287. 1s. each.

Books

W. Topley, Geology of the Weald, 8vo, London (Geol. Surv.) 1875. 285.

W. Whitaker, Geology of the London Basin, 8vo, London (Geol. Surv.) 187 2. 13s.