Excursion to Ruxley and the Crays: Saturday, September
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47 EXCURSION TO RUXLEY AND THE CRAYS. SATURDAY, SEPTEMBER 4TH, 1920. REPORT BY E. ERNEST S. BROWN, Director of the Excursion. A PART.Y of twenty-two members assembled at Sideup Station and walked south-east over the level ground of the Blackheath Beds to the top of Foot scray Lane, where the first halt was made immediately abo ve the valley of the Cray. Here the general geology of the district was described, with particular reference to the Tertiary beds through which the River Cray has cut its way down to the Chalk. Slipp ed Pebbl e Beds and Thanet Sands in situ were seen in the sides of the lane. The party then entered Footscray Brickyard, which shows good sections of brickearth, int erspersed with trails of small pebbl es, the whole overlying coarse gravels.* A worked flake of Mousterian type taken from this section in 1912 was exhibited. The party then proceeded through Footscray village, crossed the River Cray and walked south-east along the main road, pausing on the opposit e side of the valley to see the general view from that side. Just before Ruxley Quarry is reached the main road crosses the two faults shown on the I -inch Geological Survey map ,and here the Director pointed out their positi on and a bank, now over grown, where Pebble Beds with crushed shells were formerly exposed along the line of the west ern of the two faults and on a level with the Chalk outcrop. The party then entered the quarry, which is in the upper part of the M icraster cor-anguinum zone and shows severa l strong bands of nodular and one of tabular flint. Several sections of pipes are exposed on the eastern face of the pit, and there is much shallow piping on the western face. This pit, though now much overgrown, st ill yields fossils, and a quarter of an hour was spent here in collecting. It was particularly pointed out that there is no evidence of disturbance in the Chalk on the western side of the pit although this approxima tes so closely to the east ern of the two faults referred to above. Leaving the quarry the party re-assembled just above it in the lane which runs from Ruxley to Hockenden and overlooks the small trough-shaped valley outlined on the map by the two faults. Here the Director quoted much of the evidence published in support of the existence of these faults, and also the facts which throw some doubt on them. t He emphasised the un satisfactory nature of the evid ence for the faults, and maintained that hill-slip and denudation were the most probable explanation. • For diagram and detailed description see R. H. Chandler, Proc, Prehi storic Society 01 East A ngl i a, vo l. ii., Part I, 1915, pp . 81-3_ .. W. Whitaker.-" The Geology of the London Basin ." Mem . Geol. Surv ., vol. iv, (1872.) pp , 258-9· EXCURSION TO RUXLEY AND THE eRAYS. The route was resumed by field paths to the foot of St. Paul's Cray Hill, where a section of Pebble Beds was examined. This section could well represent a mass of slipped Tertiary beds after some resorting, as it shows a patch of crushed shells, patches of sand, near the top a layer of Blackheath Beds, and under them a number of large angular flints. The party then walked over the top of St. Paul's Cray Hill, where there are good lane-sections of Thanet Sands on both sides, with Woolwich Clays on the top. The outcrop of the Chalk is seen just before the main road on the river level is reached. After tea at the Bull Inn the party crossed the River Cray and proceeded by footpath to St. Mary Cray Brickworks. Here is exposed from six to ten feet of brickearth containing patches of Eocene pebbles. These deposits are of considerable extent and have been much worked. It is understood that trial holes have also recently proved the presence of equally good deposits between the Chislehurst Road and the railway embankment. Mr. Leach called attention to a thin bed of chalk rubble ce mented into hard breccia. A similar bed may be seen lower down the Cray valley in Stoneham's Pit, Crayford, and Norris's Pit, North End.* In each case, as at St. Mary Cray, the breccia separates the Pleistocene deposits from the Chalk. He regarded the deposit as an old talus, formed and hardened into breccia before the brickearth was laid down, and referred to the South African" stone-reefs"] of wind-blown sand, hardened originally by calcium carbonate derived from comminuted shells. The carbonate is first dissolved and afterwards re-deposited on the evaporation of the interstitial water and subsequently further hardened by more carbonate deposited from sea-water. At ebb tide the rock is left covered by merely a thin layer of water which, as the sun warms it, loses carbonic acid gas and deposits calcium carbonate. Some such action may, he suggested, have occurred in the Cray valley when tidal or seasonal changes caused the river to rise and fall against its chalky banks. Leaving the Brickworks the party proceeded a little way up the hill to see a good section of Thanet Sands and then divided, some to take train from St. Mary Cray, whilst the remainder walked through St. Paul's Cray Woods and across the Common, dispersing at Chislehurst. REFERENCES. Maps.-I-inch Geological Survey (Drift Edition), London, Sheet 4. r-inch Ordnance Survey (Large Sheet Series), Sheet 1I6. I872.-W. WHlTAKER.-" The Geology of the London Basin." Mem. Geoi, Survey, vol, iv.,pp. 258-259. 1874. H. WALKER.-Proc. Geol, Assoc., vol. iv., p. 155 . • Proc. CeDI. Assoc., vel. xxiii., p. 187 and Pi. 23A. t E. H. L. Sohwarz.-CasuaJ Geology. p. 62. EXCURSION TO STANSTEAD, EASNEYE, AND WARE, 49 19 09. H. B. WOODWARD.-" Geology of London District." Mem, Geol, Sur», 1910, G. E. DIBLEY.-" Excursion to Footscray." Proc, Geol. Assoc., vol. xxi., p. 196. 19 1 5. R. H. CHANDLER.-Proc. Prehistoric Society of East Anglia, vol. ii., Part I, pp. 81-83. 19 18. G. E. DIBLEY.-" Additional Notes on the Chalk, etc." Proc, Geol, Assoc., vol. xxix., p. 79. EXCURSION TO STANSTEAD, EASNEYE, AND WARE. SATURDAY, SEPTEMBER IITH, 1920. REPORT BY R. L. SHERLOCK, D.Sc., A.R.C.Sc., F.G.S., Director of the Excursion. THE Director met the party at Rye House Station at 2.5 and a start was made along the towpath of the Lea Navigation. On the left hand was noticed a high bank, on top of which the New River has been cut and which is formed of a gravel terrace. At St. Margaret's Station three more members joined, and the party then numbered fifteen. The station stands almost on the western limit of the Lea alluvial flat, which is here about half a mile wide. The flat was crossed and it was pointed out that the High Street, Stanstead Abbots, is situated on the flood-plain and is subject to occasional severe floods. It is very unusual for a village to be situated on the present alluvial flat, the usual site being on an older river-terrace, raised a little above flood level. After crossing the flat the route was northwards, along the high road, the position of which has been modified in recent years. It lies on a narrow strip of Chalk forming the lower slope of the left bank of the Lea. After walking about a mile along the road the party crossed the River Ash close to its junction with the Lea. The valley of the Ash is very sinuous and is deeply cut. Soon after crossing the Buntingford Railway the party turned off to the right and visited a chalk-pit in the M icraster cor-anguinum zone. The upper part of the pit showed narrow gravelly bands interbedded with the Chalk, apparently owing to hill-creep, for the slope is steep and the top of the hill is in glacial gravel. Pipes of the gravel were also observed. A footpath was then taken across the Ash into Easneye Park and across a small but typical patch of river-gravel, occupying the promontory within a bend of the Ash. The path follows the right bank of the stream, below the marked feature of the Reading Beds escarpment, here buried under glacial gravel. The feature is notched opposite Watersplace Farm by a small obsequent valley which is frequently dry, and has, in front of it, a well marked delta fan. PROC. GEOL. Assoo., VOL. XXXII., PART I, 19ZI• 4-.