Note on a dark coloured band in the tunbridge wells, sand at boyne park

Note on a dark coloured band in the tunbridge wells, sand at boyne park

106 EXCURSION TO TUNBRIDGE WELLS. the difficulty which rain-water finds in passing through such finegrained sandstone-a great proportion finds it ea...

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106

EXCURSION TO TUNBRIDGE WELLS.

the difficulty which rain-water finds in passing through such finegrained sandstone-a great proportion finds it easier to run off the ground, forming side valleys, than to go through the rocks. The description of what was next seen in Boyne Park need not be repeated, as it was reported in last year's PROCEEDINGS, vol. xiv, p. 198. Mr. Stocks having since then examined the .. black band," his report is appended. At 4.30 an adjournment to Nye's on Mount Ephraim for tea gave a welcome opportunity for a rest. Afterwards the party divided; the larger portion saw the exposed " Rocks" on Tunbridge Wells and RusthaU Commons. Much interest was taken in the horizontal rows of holes occurring along the planes of bedding in some of these rocks ; apparently due to percolating water assisted, possibly, by the action of frost. A short visit was paid to the "High Rocks," where similar holes were seen, and a discussion took place on the origin of the remarkable perpendicular jointing of these Rocks. A brief inspection, in a new road near Cumberland Walk, of a section of Clay (? East Grinstead Clay) in which large angular fragments of sandstone lie in most irregular order, brought the excursion to an end. NOTE ON A DARK COLOURED BAND IN THE TUNBRIDGE WELLS, SAND AT BOYNE PARK. By H . B. STOCKS. ON testing a portion of the dark-brown and black sand from Boyne Park it was found that the colouring matter is not extracted by hydrochloric acid, but is quite soluble in caustic soda, yielding a dark-brown solution, from which hydrochloric acid precipitates a brown flocculent substance. On igniting the sand the black colour disapp ears with incandescence, and carbonic acid is formed ; therefore the colouring matter is organic, the ignited sand has only a pale reddish -yellow colour. Iron is present only in small quantity, and manganese is absent. Taking these facts into consideration, it appears that the material colouring the sand is organic matter and of the nature of "humic" acid. This humic acid is probably derived, by solution in rain water, from the humic acid in the overlying soil and the redeposition of it in certain lines in the strata below. In order to explain the causes for the redeposition of the humic acid, further examination will, however, be required.

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108

EXCURSION TO CHISELHURST.

REFERENCES. Geological Survey May, Sheet 6 (Drift Edition). Price 8s. 6d. Ordnance Survey Map (New Series), Sheets 287, 303. Price IS. each. 1875. W. TOPLEY.-" The Geology of the Weald," Mem. Geo]. SUl'vey. 1879. W. FAWCETT.-" Excursion to Tonbridge and Tunbridge Wells," See II Record of Excursions," page 38. 1895. R. S. BERRIES AND G. ABBOTT.-" Excursion to Tunbridge Wells," Proc. Geol. Assoc., vol. xiv, p. 198. 1896. H. G. SEELEY.-" Note on Current Bedding in Clays." BritISh Assoc. Report, p. 805.

EXCURSION TO CHISELHURST. MAY

Directors:

15TH,

1897.

W. WHITAKER, F.R.S., AND

Excursion Secretary:

W.

P. D.

T. V.

HOLMES, F.G.S.

STEBBING, F.G.S.

(Report by THE DIRECTORS.)

ON arrival at Chiselhurst railway-station the party proceeded in a north-westerly direction along the road close to, but east of, the railway, passing, near the station, a large old Chalk-pit on the right, too much overgrown to be worth visiting. A halt was made at the corner of Camden Park, where the Chalk was once worked by means of horizontal galleries extending for a considerable distance under the Park. These galleries were inspected by members of the Association when Chiselhurst was visited in 1872, the owner having them illuminated for that purpose. They are now too much choked up to be worth entering. The mouths of some of the galleries are still visible, but as building is going on in front of them they will soon cease to be as conspicuous, both from road and railway, as they have been hitherto. Mr. Whitaker drew attention to the compactness of the Thanet Sand, which stands, with a nearly vertical face, above the Chalk, to the fairly even junction of the two formations, to the presence of a marked firm bed in the Chalk (which forms the roof of the galleries), and to the fact that the Chalk has been worked to a greater depth than formerly, and that though the deep part of the pit was a little below the level of the neighbouring stream, yet there was no water in it. On leaving Camden Park pit the railway was crossed, and recrossed south of the tunnel. Near by the mouth of the tunnel, and east of Elmstead Lane, is the pit in Rockpit Wood, showing the Blackheath Pebble Beds, which the Association was enabled to visit by kind permission of Sir Samuel Scott, Bart. Here, instead of unconsolidated beds of pebbles and sand, the pebble-beds were JULY, 1897.]