176 EXCURSION TO T WYFORD A ND THE WARG R AVE OUTLIER. of a similar character to that seen before, except that liver­ coloured quartzites and other stones suggesting a Bunter origin were found. No Lo wer Greensand chert was seen at either of the pits. A pleasant walk, mostly through fields, brou ght the party to Pinn er Station, and an enjoyable excursion to a close.

RE FERE"CES. Geol ogi ca l S ur vey Map, S heet 7. Drift Edition. (Price 18s. Ordnance Survey Map, S heets 255 and 256. ( Price IS. each .)

1889. \ VHITAKER, \V.-" Geo logy of London ." Vol. i , Mem. Geol. Survey. 1 890 . PR ESTWICH, S I!{ J.- "On the Re lation of th e Westleton Beds, or Pebbly San ds of Suffolk, to those of Norfolk, and on th eir Extension Inlan d." Q.:J.G..!>:, vol, xlvi, p. 84 . MON CKTON, H. W., a nd B ERRIES, R. S.-" On some hill gravels N. of the Thames." P roc, Geo! Assoc., vol. xii, p. ra8. SALTER, A. E.-" Pebbly G ra vel from Goring Gap to the N orfolk Coast." Proc, Geoi, A ssoc., vol, xiv, pp. 389, et seq. 190 0 C. REID.-" Su mmary of Pr ogress ," 189). Mem. CeDI. Survey.

EXCURSION TO TWYFORD AND THE OUTLIER.

SATURDAY, JULY 6 T H , 1901.

D irectors : LL. TREA CHER, F.G.S., A ND H. J. OSEORNE 'VHITE, F.G.S. E xcursion Secretary: W. P. D. STEERI NG, F.G.S.

(Rtpo," by H. J. OSBORNE W HITE.)

THE members arri ved at T wyford about noon, and, meeting the Directors at the stati on, were conducted through the village to Mr. Treacher's residence, where about half an hour was spent in examin ing a portion of the large and valuable assemblage of stone and bron ze implements, mammalian bones, and other obje cts of geological interest collected by the senior Director in the South of . In view of the visit of the Association, the glass tabl e-cases in the museum had been arranged, as far as possible, so as to illustrate the local geology, but in the short time at their disposal the members were able to gain only an imperfect impression of the varied character and importance of the whole collection. Especial interest was manifested in the fine series of Palreolithic tools of flint and quartzite, obta ined from the middle and lower E XC UR SIO N TO T WYFORD AND T HE WA RGRAVE OUTLI ER . 177 terraces of river-gravel at R uscombe, Caversham , Maidenhead, and other places in the valley of the Upper Thames ; and the peculiarly massive character of some local specimens of the pointed type was a subject of comm ent. Amon g the examples of neoliths, collected from a somewhat wider area, a delicately­ fashioned flint scraper, of the lunate form common in the Danish kitchen-middens, dredged from the T hames at Cook ham, also attracted attenti on. Of the local fossils, ment ion may be made of a flint cast of a large ammonite of the leptophylllts group, from the Upper Chalk of the Waltham cutting on the G.W.R. After refreshing themselves with the fruit kindl y provided by Mrs. Treacher in the library attached to the museum, the mem­ bers proceeded through the adjoining garden and meadow to Mr. Cott erell's brickyard, at Rus combe. Here attention was first directed to the dep osit of implement-bearing gravel overlying the Reading clays and sands. This gravel consists mainly of sub­ angular and pebbly flints, with a noticeable number of the red and brown Bunter quartzite-pebbles characterising the Thames Valley Gravels, and of the partly rounded pieces of Lower Green­ sand chert occurring in the Southern Drift of the Loddon basin. It is really a mixture of two distinct gravels, the one essentially of north-western, the oth er of southern origin ; and while the gently sloping area about Ru scombe now lies whollywithin the basin of the Loddon , it must, at one time, have formed the debatable ground at the junction of that river with the Thames. In a section open ed on the northern side of the brickyard, in 1893, a gravel of purely southern type was to be seen underlying one of north­ western facies. Th e gravel seen in the western end of the workings on the present occasion had a much disturbed appear­ ance, the stones being mixed with, and obliquely piped into the underlying sands and clays ; but elsewhere the stratification was quite dist inct, and the deposit clean and sandy. Turning to the solid rocks, the Directors pointed out the variable and impersistent characters of the sands, loams, and clays forming the higher beds of the Reading Series at this spot. The pits surroundi ng the yard were all opened at ab out the same level, but the sections exposed in them possessed few features in common, and the succession of the beds had to be traced in a horizontal, rather than in a vertical, direction. At the north­ western corner of the workings evidence of contemporaneous erosion was shown with diagrammatic clearness. A bank of stiff grey clay, with faint reddish mottlings and indistinct trac es of bedding towards the top, exposed to a depth of about 15ft. below the gravel, had been deeply channelled, and the hollow thus formed subsequently filled in with grey and yellow sands, the latter minutely current-bedded. T owards the south these sands were succeeded by loams with seams of light grey clay, affected by a strong south-easterly dip (apparently the result of current-bedding 178 EXCURSION TO TWYFORD AND THE WARGRAVE OUTLIER.

on a large scale), followed by horizontal beds of yellow and crimson-stained sands, rapidly giving place to a four-foot band of pale, bluish-mottled clay, resting on yellow sand. The southern face of the yard showed only banded mottled clay, exposed to a depth of between 20 and 30 ft., and forming part of a broad lenticular mass, on whose gently sloping flanks the beds previously seen appeared to rest. The state of Mr. Treacher's health not allowing of his accompanying the party beyond , Mr. Osborne White, who took charge of the excursion during the rest of the day, led the way across the Bath Road, and by footpaths to the large chalk-quarry south of Wargrave. Here was exposed a fine vertical section, some 60 ft. in height, in the higher part of the Upper Chalk, belonging to the zone of Micraster cor-anguinum. The rock possessed the usual, somewhat friable, multi-jointed character, with frequent bands and floors of nodular flint, and a few subordinate seams of the tabular variety. A band of chalk, of more marly nature, was noticeable at about 3 ft. above the base of the section. Fossils are neither abundant nor well­ preserved in this pit, but forms characteristic of the zone have been obtained by local collectors from time to time. The Director having pointed out the principal features of the section, and briefly explained the somewhat dangerous method of getting the chalk, by undercutting, employed at this spot, the members resumed their walk through the pleasant country on the western slope of the Wargrave Tertiary outlier to the "Horns Inn," near , where a short stop was made for rest and refreshment. Time did not permit of a visit either to the pit in Mr. Keeley's brick-yard at , which is interesting chiefly by reason ofthe unusually large variety of the clays there occupying a hollow in the light-coloured sands forming the upper part of the Reading Beds, or to the road-side exposure of the thin band of unfossiliferous sandy limestone at the base of the London Clay, near Holly Cross. Lunch concluded, the members of the party ascended Bowsey Hill, but the fine view up the Kennet valley, usually to be obtained from the summit, being obscured by haze, they at once turned into the beech wood on the north-eastern slope, where a few paces brought them to the newly-opened pits in the largest of the patches of pebble-gravel that cap the I S0 feet or so of London Clay forming the higher part of this eminence. Classed by Sir Joseph Prestwich with his inland extension of the marine shingle typically developed at Westleton, near the Suffolk coast, in 1890, the Bowsey Gravel has been frequently examined and described by other observers in later years; but its true origin and age-as also those of the other pebbly hill gravels scattered along the northern slope of the London Basin-are still very doubtful. The deposit examined on the present occa- EXCURSION TO TWYFORD AND THE WARGRAVE OUTLIER. 179 sion appeared to be irregularly banked against the higher part of the north-eastern slope of the hill. In many places it contained a large admixture of brown clay from the underlying rock, but, although probably nowhere strictly in situ, its evenly-bedded character, and the purity of the yel1ow, and partly iron-cemented sand associated with, or separating, the bands of pebbles near the base of the deepest section, suggested that the amount of disturbance it had suffered had been but slight. The Director remarked that although the gravels grouped as Westleton Beds by Prestwich -varying markedly as they do both in the nature and in the proportion of their constituents-had been found capable of sub-division into a number of tolerably distinct varieties, he thought that-so far, at least, as the patches in the north-western district of the London basin were concerned-they might be satisfactorily placed, according to their composition, under one or other of two heads, viz., (I) a simpler and (2) a more complex. Of these, the first consisted of little but flint and quartz; the second contained a noticeable proportion of other rock frag­ ments, amongst which the pebbles of pale-tinted quartzites, dark encrinital chert, banded lydite and veinstone, and a variety of compact and felspathic sandstones were the most prominent. The more complex type, of which the Bowsey Gravel might be regarded as a good example, appeared to be unrepresented in that part of the London basin drained by the Kennet, while the simpler kind found at Nettlebed and Greenmore, in Oxon., and elsewhere, had been traced westward to beyond Marlborough. After a general discussion on the possible ages and modes of formation of the deposit, in the course of which the President commented on its strong resemblance to the shingle at Westleton Common, and its unlikeness to any of the admittedly Eocene pebble beds occurring in the London basin, the members searched the heaps of stones removed from the pits, whence they speedily obtained specimens of the principal varieties of rocks represented, including a 6 inch cube of white vein-quartz. Following the track down the hill-side the party crossed a small, sharply cut valley, where, to judge by the frequent traces of recent slips, erosion is still very active. On reaching Warren Row they proceeded eastward along the road as far as the edge of the common, where the Upper Chalk-locally employed in the manufacture of" whitening "-is obtained from underground gal1eries. The entrance to the older galleries was completely blocked by a smalliandslip a few years ago, but the newer and less extensive workings are readily accessible by means of an adit opening into a smal1 chamber of irregular plan, from which the headings diverge. The attention of the members was directed to the continuous bed of nodular flints, utilised as a roof to the workings: and to the numerous bands of stiff clay, exhibiting a sort of foliated structure, that had been forcibly squeezed into the 180 EXCURSION TO TWYFORD AND THF. WARGRAVE OUTLIER. joints of the chalk-probably on the occasion of the slip above referred to. The sides of the open pit near the mouth of the adit showed the following section :- 5. Clay Soil. Feet. 4· Compact brown and grey sandy clay, with layers LOCAL DRIFT. and masses of pebbles derived from the gravel i on the higher ground in the vicinity 6-10 BOTTOM OF \ 3. Laminated brown sandy clay 2 READING ~ 2. Large, unworn, green-coated flints, with a few BEDS. l small flint pebbles, in grey and greenish sand ... I 1. Chalk, traversed by tubular cavities or borings filled with greenish sand to a depth of 3 feet below its even junction with bed above; and with layers of flint nodules. It was noticed that the above-mentioned borings, starting at the upper surface of the chalk, pursued regularly curving courses, independent of joint-planes, and while invariably circular in transverse section, appeared in some cases to taper downwards. In a few instances their sandy infilling was absent, its place being occupied by a plug of chalk, which could be removed like a sample of cheese from a taster, leaving a tube from half an inch to an inch in diameter, on whose slightly stained surface a faint striation was visible. The majority of the members present seemed disposed to agree with Mr. W. H. Hudleston in attributing these curious tubes to the boring action of the roots of marine plants. A short distance to the north-east of this spot the party was introduced to a pretty example of a calcareous spring, issuing from the upper sands of the Reading Series, on the slope of Ashley Hill. The water is highly charged with carbonate of lime, which is deposited as a brownish-grey crust on the twigs, chips of wood, pebbles and other objects in the bed of the ditch conducting it to the swallcw-hole at the foot of the hill. Some of the specimens of "petrified" wood obtained showed only a thin granular, or oolitic, coating; others possessed a hard crust, still retaining the form of the stick, or twig, within; while in yet others the original nucleus had entirely disappeared, leaving a hollow or solid, roughly cylindrical, nodule of tufa. The rarity of such springs in the Tertiary areas of this country gives this example a peculiar interest. The thin bed of limestone occurring at the base of the London Clay is the most likely source of the calcareous matter. Crossing the low ridge connecting Bowsey and Ashley Hills, the members reached Mr. Warner's brickyard, at Knowl Hill. In the numerous pits here opened, at different levels, in the ground rising towards the eastern spur of Bowsey, the following suc­ cession of beds, belonging to the Reading Series, could be made out- EXCURSION TO TWYFORD AND THE WARGRAVE OUTLIER. lSI

Feet. 5. Yellow and orange sands, occasionally current- bedded ... about 20 4. Bluish-red mottled clay, with signs of bedding towardsthe top 20 (3. Compact, pale blue clay, with loamy partings 2 2 . Laminated blue, grey and lavender clays, with 1 lenticlesof light yellow and brown sand, iron- LEAF-BEDS. -{ cemented in places ...... It I. Alternations of ash-grey clay, and sulphur-yellow sand, strongly current-bedded towards the lower IL part 13 three feet below which a bed of "gravel with oyster shells," resting on the Chalk, was said to have been encountered. The leaf-beds here occupy much the same position in the Reading series as they do at the type locality. How far they extend beneath the Warzrave outlier is not known, for the brick­ yard excavations are rarely carried below the base of the main bed of mottled clay, which, in this district, forms the most economically valuable, as well as the most persistent, member of the series; but they are probably quite local. Few, if any, of the many bands and seams of clay in beds I to 3 are devoid of impressions or coats of vegetable matter, and those of land 2 are particularly rich in the remains of leaves, stems of reed-like plants, and seed cases. The yellow sands near the base of the section, also, contain small pieces of lignite. A short search yielded a number of good specimens of leaves, in some of which the impression of cellulartissue could be clearly detected, and it wasnoticed that a common variety, of lanceolate form, was alone represented along one fairly well-marked horizon. A rapid survey of the overlying clay and sand bringing the day's work to a conclusion, the members took tea at the Seven Stars Inn, where the President, in proposing the customary vote of thanks to the Directors, feelingly referred to the loss which the Association had recently sustained in the death of his old col­ league, John Hopwood Blake, of H.M. Geological Survey. The geologists then returned to Twyford by the Bath Road, in time for the 7.7. p.m. train to London. REFERENCES. New t-inch Ordnance Maps, Sheets 254-5, 268-9. Geological Survey Map, Sheet 7 (Drift). 1889. WHITAKER, W.-"Geology of London." Vol. i, pp. 552 and 555. Mem. Geol. SI~rvey. 1890. PRESTWICH, J.-" On the Relations of the Westleton Beds," etc. Quart. yourn. Geo!, Soc., vol, xlvi, p. 141. r891. BLAKE, J. H.-Report and Proc. Reading Lit.and Scientific Soc.,p. 28. r892' WHITE, H. ]. 0.-" Notes on the Westleton Beds near Henley." Proc. Geol. Assoc.. vol. xii, p. 379. 1893. MONCKTON, H. W.-"On the Occurrence of Boulders and Pebbles from Glacial Drift," etc. Quart. Jount. Geol Soc., vol.xlix, p. 315. 1898. SHRUBSOLE, O. A.-" On High Level Gravels in Berks. and axon." Quart. ]ourn. Geol. Soc., vol. liv, p. 587. PROC. GEOL. Assoc., VOL. XVII, PART 4, AUGUST, 1901.] 13