204 EXCURSION TO HENLEY-ON-THAMES AND NETTLEBED.

\Vidford, where they were joined by some of the members of theEssex Field Club who had been for a botanical ramble under theguidance of Mr. E. Durrant, one of the Hon. Sees. of the Essexand Chelmsford Museum.

On their return to Chelmsford, the united party found an excel­lent tea provided at the Saracen's Head Hotel. Mr. E. A.Fitch, the President of the Essex Field Club, occupied the chair,and Mr. T. V. Holmes, a Vice-President of both Societies, thevice-chair. On the proposition of Mr. Holmes, seconded byMr. Fitch, a cordial vote of thanks was given to the Director.After tea, on the invitation of Mr. Durrant, some of the membersvisited the church and museum. The return train left Chelms­ford at 7.50 p.m.

REFERENCES.

Geological Survey Map, Sheet I, N.E.New Ordnance Survey Map.Sheets 240,241,1887. WOODWARD, H. B.-" Geology of England and Wales," znd edition,

p. 506, fig. 89. Section at Writtle, near Chelmsford.1889. WHITAKER, W.-" The Geology of London," vol. L, p. 318, Ceol.

Survey Mem.1890. HOLMES, T. V.-" On the Chelmsford Water Supply," Esse» Naturalist,

vol. iv., p. 82, April-june.

EXCURSION TO HENLEY-aN-THAMES ANDNETTLEBED.

SATURDAY, JULY 18TH, 1891.

Director: J. H. BLAKE, F.G.S., Assoc. M.Inst. C.E., ofH.M. Geological Survey.

(Report by THE DIRECTOR.)

About forty members of the Association arrived at noon atHenley, where they were met by the Director. The partydrove northward in brakes and carriages to Henley Park, andalighted at the Chalk-pit at the foot of the hill.

Here a fine section of what is known as the" Chalk Rock" isexposed, intervening between the Upper and Middle Chalk. TheDirector drew attention to its special characteristics, and explainedthat it was a hard band of cream-coloured limestone, not muchmore than 3feet thick in that locality, and that it contained through­out its mass numerous brownish calcareo-phosphatic nodules,irregular in shape, and green-coated; together with decomposediron-pyrites in places. Numerous joints occurred in it at rightangles to its plane of bedding; and, whilst its upper surface pre­sented a comparatively even and very marked line, its under

EXCURSION TO HENLEY-ON-THA~IES AND NETTLEBED . 205

surface merged more or less into the underlying beds. Conse­quently, it was classified as ' th e uppermost bed of th e MiddleChalk ; and, whilst num erou s lines of flint occurred in the Chalkabove this bed of rock, but very few flints occurred in that belowit, The thickness of the Upper Chalk in this district was nearly300 feet, and the thi ckn ess of the Middle and Lower Chalk com­bin ed was about 350 to 400 feet, mak ing a total thickness of from650 to 700 feet.

The Chalk Ro ck was carefully examined, and some fossilsobtained from it, thou gh they are not so abundant here as theyare in some oth er localiti es.

The members th en walked ove r No Man's Hill, from theto p of which th e fine view of H enley and the sur rounding neigh­bourhood was much admired. Before descending, the Directorstated that the surface of the hill consisted of a ter race or platformof gravel overlying Chalk, 315 feet above Ordnance Datum, and2 IO feet above the Thames at H enley. He also describ ed whathe considered to be the origin of the more or less horse-shoeshaped curve of the Thames from Wargrave and H enley toMaidenhead; and pointed across the valley to Remenham, whereanother comparatively level terrace or plateau of gravel occurredon the Chalk, but at a little more than IOO feet ben eath the levelof the plateau on which they were standing.

A descent was th en made by footpath s to the road, where thebrakes and carriages had been brou ght round, and the partyproceeded therein to Net tlebed-four and a-half miles distant­arriving there at about 2.30 p.m. T he village is partly situated on,and partly adjoins an outli er of Reading Bed s, varying in diameterfrom ab out five-eighths to three-quarters of a mile. The DriftPebble Gravel at Pri est's H ill was first examined. It was shownto consist mostly of flint pebbles or shingle, with num erous smallquartz pebbles intermixed, and to rest irregularly on 6 feet or moreof whitish sandy drift, probably derived from the adjacent ReadingBeds on which it lay. Its level is ab out 560 feet or more abovethe Thames at H enley, and 66 5 feet or more ab ove OrdnanceDa tum. It was considered to be a marin e Pre-Glacial hill-drift,and was correlated by Prof. Prestwich with his so-called " Westle­ton Shingle " * of the East of England, which deposit is exhibitedin th e cliff sections around the Norfolk and Suffolk coast, over­lying the Pliocene " R ootl et Bed" or Forest Bed, and und erlyingth e Glacial Lower Boulder Clay.

A circuit of the Outlier of Reading Beds, capped with LondonClay, was then made, and many interesting sections were visitedon the way. These exposed crimson and grey mottled clays, andvariegated coloured sands of the Reading Beds; they lay beneaththe Basement Bed of the London Clay, and a line of flintpebbles occurred at the junction. The Basement Bed, about

. .. Bu re Valley Beds." of Searles Wood.

206 EXCURSION TO HENLEY-ON-THAMES AND NETTLEBED.

7 feet in thickness, presented its usual character, consisting ofthin seams of grey and brown clay, inter-stratified with brown andolive-coloured greensand containing numerous glauconitic grains;interspersed are nodules of clay-ironstone, flint pebbles, and here,and there a few ferruginous casts of shells. A clearly definedfault running in a north-westerly and south-westerly direction,with a down throw of 7 feet to the north, was well exposed insection; and the Basement Bed of the London Clay was seenside by side with the Reading Beds.

The summit of the Outlier at Windmill Hill, 696 feet aboveOrdnance Datum, was eventually reached. Here an extensiveview was obtained across the Thames Basin. The Chalk, whichrises from beneath the Tertiary Beds on the southern side, andwhich forms the highest ground, was seen, the Hog's Back andother physical features being clearly discernible. An inspectionof a section of the Basement Bed of the London Clay at thispoint was then made. This bed showed, at its juncture withthe Reading beds, unusually large flint pebbles or boulders, somemeasuring from 6 to I I inches in size. The latter beds are herewhite and yellow sands, mottled with crimson, and indurated inplaces from the presence of iron. Various patches of the DriftPebbly Gravel, or so-called Westleton Shingle, were observed indifferent places in making the circuit of the Tertiary outlier, butnone were noted on its summit, the London Clay being thereapparently free from any.

A visit to some adits or headings in the Chalk, driven beneaththe Tertiary outlier, and lit up with candles and magnesium wire,concluded the day's explorations.

After tea at the Bull Inn, Nettlebed, the party had a verypleasant drive back to Henley, and returned to London by the6.30 p.m. train.

REFERENCES.

Geological Survey Map, Sheet 13.New Ordnance Survey Map , Sheet 254-1854. PRESTWICH, J-" The Woolwich and Reading Series," Quart. Your».

G~ol. Soc., vol. x., p. 89.1872. WHITAKE~, W.-"The Geology of the London Basin," Mem. Geoi,

SUr1'~Y, vol. iv. , pp. 48, 204-206, 305, &c.1890. PRESTWICH, J.-" On the Relatlon of the Westleton Beds or Pebbly

Sands . .. and on the Elevation and Denudation of theWeald and of the Thames Valley," Quart. Yo,,,.n. Geol. Soc., vol.xlvi., pp. 140-150.