87

FIELD MEETING IN THE HITCHIN DISTRICT.

SATURDA Y , J UNE 15th, 1929.

REPORT BY E. F. D. BLOm.l , M.A., n.sc, AN D

S. W. WOOLDRID GE, D.Sc., F.G .S.

[Received November 12th, 1929.]

THE party, consisting of 20 members of the Associationand 8 others, who were specially invited, assembled at

Hitchin Station at 10.30. The hired conveyances for the tourof 25 miles were supplemented by four private cars. The Lutonroad was followed as far as Offiey village, where by a steepgradient the level of the Chalk rock is reached at an alti tude ofabout 500 feet. A short stop was made at the village schooland evidence of the capping of boulder clay was shown, a speci­men of clay from an old brickworks in the village and of anigneous boulder from the School garden being exhibited by Mr.Bloom. The party then proceeded by an attractive privateroad fringed with beechwoods through Wellbury Park and a stopwas made at some old gravel workings (520 feet O.D .), where alarge block of gravel conglomerate is exposed above the presentground level. It is understood that the block was formerlymuch larger, but part of it ha s been blasted away for road­mending. Probably when th e original pit was dug the softe rmaterial was removed all round it , leaving th e block high anddry and giving it the ap pearance of an ice-transported' erratic.'It was here seen that th e principal constituents of thegravel were chalk pebbles and flints, t ogether with a va riety ofMidland rocks and fossils, the cementing material bein g cal­careous . Similar material is to be found at several othe r localities.near Hitchin, e.g., Bygrave, Willian , Hitch Wood.

Dr. Wooldridge took this opportunity to explain the genera laim of the day 's excurs ion and to describe the main geologicalfeatures of the district . He mentioned that the chief featureof the programme was to examine the distribution of glacialdri ft in the district, particularly the high level drift along thescarp. He expressed th e opinion that the Chilterns west of theHitchin gap acted in the main as a barrier to Midland ice, butthat here and there the drift was pushed up on to the scarp.A large mass of drift passed through the Hitchin gap andtravelled as far south as Hertford, where it met the ice-bornematerial which had overrun Essex and was pushed far up theLea Valley.

Mr. Bloom said that he was in general agreement withDr. Wooldridge's statements, but speaking from local know­ledge he was inclined to think th at there was evidence of thedrift pushing through min or gaps west of Hitchin , and he hoped

88 E. F. D. BLOOM AND S. W. WOOLDRIDGE,

to show the party such evidence in the case of the Mimram valleylater in the day. Since boulder clay was found as high as 520feet and glacial gravel at nearly 600 ft. on Lilley Hoo it was clearthat the Midland ice must have over-lapped the scarp to someextent at these points, and during the melting period, if notearlier, debris must have been transported southwards alongthe consequent valleys.

The journey was then resumed by the private road on tothe Hitchin-s-Hexton road, and after crossing the Icknield way,here a green road which passes direct to the top of TelegraphHill (600 ft. O.D.), the party halted at the foot of Beacon Hill.This was ascended to a height sufficient to give a view over theBedfordshire plain, and the topographical and geological featureswere described by Mr. Bloom. The excellent panoramic viewfrom this point looking over the Chalk Marl-Gault plain to thegreensand hills of Bedfordshire was generally admired.

At one mile from the village of Hexton the cars were parkedin a lane leading to the downs and the party ascended by anarrow chalk coombe to the top. Here a very interestingexposure of glacial gravel at an altitude of 500 feet and lying ona shelf at the Melbourn rock level was inspected. The gravelis very evenly bedded with a slight dip to the east and containsnumerous chalk pebbles, angular flints, Bunter quartzites, quartzpebbles, red chalk, carstone, red sandstone, Carboniferous chertwith crinoid stems, and pieces of carbonised wood. Belemnitesare numerous (chiefly B. mmimus) and Gryphseas and Ostreasare frequent. Layers of sand are interbedded with pebblygravel. The soil above contains some elements of a sandyheath flora, and it is evidently sterile. Farther south, however,on the other side of a dry valley (Church Hole) is cornland at thesame altitude, and the soil, though still gravelly, contains largererratic boulders and evidently has a greater clay content. Abouthalf a mile to the S.W. at a somewhat higher altitude is a patchof boulder clay supporting woodland (Oak, Ash, Hazel).

The downs at this point form a plateau, with an altitudeof about 500 feet, curiously dissected in all directions by deepcoombes, the largest of which is the Burwell valley. Thisvalley makes a horse-shoe bend from its head to the village ofHexton. The upper part of it is dry, but at the middle of thebend, where it crosses the outcrop of the Totternhoe stone, anobsequent stream rises, and its water finds its way throughHexton Park to the lvel and so to the Ouse. On a spur formed bythe bend of the Burwell and its lateral valley (Church Hole) is theancient British Earthwork known as ' Ravensburgh Castle,' nowunfortunately planted with trees. It would be difficult to find inthe Chalk country a more commanding and more easily defendedhill, and its natural defences have been further strengthenedby a triple line of earthworks. About three quarters of a

FIELD MEETING IN HITCH IN DISTRICT. 89

mile to the west is another valley with laterals, similar to theBurwell valley, running down to the village of Barton-in-the­Clay. This also contains a vigorous stream issuing from springsat the Totternhoe level (about 350 ft. a.D.), which is cutting asmall valley within the larger one; the stream, like the Burwell.evidently had its source originally at the Melbourn rock level,about 450 ft. a.D. The Meg (I mile E. of Hexton) shows preciselysimilar features.

Mr. Bloom put forward for discussion the following theoryas to the origin of these valleys and the way in which theywere affected by the ice. He regarded the main features ofthe drainage as pre-glacial, but considered that the valleyshad been widened and deepened by the ice itself or by its melt­waters. 'Consequent' streams like the Mimram probablyhad their source originally at least as far north as the presentescarpment-line, while others, e.g., the rivers which formedthe Luton and the Tring gaps, rose much farther to the north­west before the chalk was denuded from the Midland plain.During the long period of denudation the sources of consequentstreams would progressively retreat, while advancing obsequentstreams would assist in the wearing down of the scarp, sometimesfollowing the line of 'wind-gaps' and sometimes eating backobliquely into former valleys of 'consequents.' The Burwell,for example, whose valley first heads south and then makes acomplete half-circle, appears to have eaten back to the Mimramvalley, and the Barton brook narrowly missed doing likewise;only a narrow col separates the upper portion of their valleys,now dry. It will be understood, of course, that this process ispresumed to have occurred when the water-table in the chalkstood higher and springs issued from the Melbourn rock levelin this particular area. At Hitchin, 6 miles to the east, theMelbourn rock is still the source of various streams, but owing tothe dip of the strata its outcrop is there at the zoo ft. a.D. level.

During the period of increasing cold the resorting of materialcaused by the seasonal melting of local ice-caps may accountfor the formation of 'Clay-with-Flints,' the material being de­rived partly from the London Clay and Reading beds. relics ofwhich probably existed as far as the crest of the Chalk escarp­ment, and partly from the Upper Chalk. Much of the Clay-with­Flints was later stripped off completely by the Midland icesheet, and was either carried away by the ice to be resortedlater during the melting or was heaped up in parts so as to givethe Clay-with-Flints an abnormal thickness locally.

Lunch was eaten near the gravel pit and afterwards a circularwalk of about a mile was taken so as to inspect the heads of thevarious valleys dissecting the plateau. Commanding viewsof the Bedfordshire plain were obtained, and a large field of sain­foin in bloom afforded a richly coloured foreground to the dis-

90 E. F . D. BLOO:\I AND S. W. WOOLDRIDGE,

tant purple. South of the scarp the character of the downshas been considerably altered here by extensive plantations ofconifers and beeches for game cover, but the scenery cannot besaid to have been spoiled.

After leaving the downs a traver se was made down theMimram valley as far as Lilley Bottom, whence the dire ct routeto Hitch Wood was taken. A short stop was made at GravelHill (507 ft . O.D.), where a roadside expo sure in Chalky BoulderClay and Gravel (contorted) was examined. The occurrenceof glacial drift in the Mimram Valley at intervals from theChalk scarp downwards suggests th at it may have been by thisroute that the large deposit s of gravel near Codicote reachedtheir present position.

The superficial deposits near Hitch Wood are mainly Clay­with-Flints, but Eocene flint pebbles and quartz pebbles occur.and at one spot there is a block of conglomerate containingthese pebbles together with material of Midland origin. Near th ewood on the side of the valley through which the road from Hitchinto Whitwell runs is an excellent exposure of Chalk Rock contain­ing numerous fossils and green ph osphate nodules. S. A. Billing­hurst has described two new species of Ammonoidea obtainedfrom this pit. (Reference 4. )

A call was next made at a gravel pit below Vicars Grove.3 miles from Hitchin, in a small lateral of the main Hitchin ­Langley Valley now filled with drift to a considerable depth.The st ruct ure of the fluvio-glacial outwash of the dist rict was.here seen to advantage, and a varied assortment of far-travelledmaterial , including a number of igneous and metamorphic rocks.was inspected. Among other specimens found here are laur­vigit e, olivine dolerite, showing spheroidal weathering, weatheredgranites and gneisses, mica-schist s, arkose and various quartzites.Th e bedding of the sand and gravel and th e step-faulting are wellshown.

On the return journey to Hitchin the positi on of th e deeppre-glacial channel described by William Hill (References 2 and3) and of the Palseolithic Lake Bed (Ref. I) , the floor of whichwas crossed at one mile from Hitchin, were pointed out.

Tea was taken at Hobley's Restaurant, and a vote of thanks.to th e Directors was proposed by Principal A. ] . Bull, to whichthe Directors suitably responded. Mr. R. L. Hine, author of ' TheHist ory of Hitchin,' also made a short speech to welcome theAssociation to Hitchin, and said he felt it was a slight to such aninteresting neighbourhood that the last excursion of th e G.A.was so long ago as 1912. He hoped that the interval betweenthis and the next would be much shorter.

After tea those members of th e party who elected to stay tillthe 7-7 p.m. train were cond ucted to the old Clay Pit belongingto Mr. The odore Ransom, situa ted near the Cemetery. From this

FIELD MEETING IN HITCHIN DISTRICT.

the fine collection of Acheulian implements, now partly housed inthe Museum of Archseology and Ethnology, Cambridge, and partlyin the possession of Mr. Francis Ransom, was obtained (ReferencesI and 6). The pit has been disused for many years and there islittle hope of further discoveries, but a section of the' brickearth'from the base of which the flint implements were obtained, is stillvisible. Mr. Bloom mentioned that Clement Reid regarded itas a mixture of ' wind-transported material and rainwash' andplaced it in the Steppe period, but there were many difficultiesin accepting this view. He himself could see little differencebetween it and certain other admittedly glacial drift, and wasinclined to attribute its deposition to a re-advance of the iceafter a period of temperate climate during which the underlyingalluvium containing freshwater plants, mammalian remains, etc.,was deposited. The recent work by Reid Moir at Hoxne inSuffolk seems to confirm this view.

References.Maps Topographical, O.S. Sheet, 95, Popular Edition.

1.-1897. CLEMENT REID. The Palzeolithic Deposits at Hitchin. Proc:Roy. Soc., vol. lxi.

2.-1908. W. H1LL.-A deep channel of Drift at Hitchin. Quart. [ourn,Geol, Soc., vol. lxiii.

3.-1912. W. Htr.t.i-s-Report of an Excursion to the Hitchin and Steven­age Gap. Proc, Geol, Assoc., vol. xxiii., pp. 217-224.

4.-1927. S. A. B1LLINGHURsT.-On some new Ammonoidea from theChalk Rock. Ceol. Mag., vol. lxiii.

5.-1924. R. L. SHERLOCK.-Superficial Deposits of S. Herts. and S.Bucks. Proc. Ceol. Assoc., vol. xxv, p. 14.

6.-1891. W. H1LL.-Journal of Hitchin Natural History Club' OurForgotten Lake: