EXCURSION TO THE BERWYNS.

had travelled from the coast to do so and had to return thatevening .

Mr. Wilson, having expressed his great pleasure in meetingthe Association, the party then proceeded to Lower Halling,which was reached in good time for tea, which was served in anadmirable manner, amid pleasant surroundings, by Mrs. Brigdenat the Manor H ouse.

After the usual votes of thank s, the members left Halling bythe 7.5 I p.m. train for home.

EXCURSION TO THE BERWYNS.

JULY 31ST TO AUGUST 7TH (LONG EXCURSION), 1908.

Director : J. LOMAS, A.R.C.S., F.G.S.

Excursion Secretary : H. KIDNER.

(R,po,.t by THE D I?ECTOR.)

A PATHETIC interest att aches to the publication of the followingaccount as it was completed by Mr. Lomas only a few weeksbefore his untimely death. Those who took part in the BerwynExcursion will long remember it as one of the most pleasant andinstru ctive that the Association has carried out, and not a little ofthe pleasure was due to the good temper and kindl iness, the energyand enthusiasm, of the Leader, who had sacrificed no smallfraction of his holiday in order to conduct the excursion.

Mr. Lomas had arranged to visit Algiers in the ChristmasVacation in order to investigate there certain phenomena whichpromised to throw some new light on a subject always of greatinterest to him--the origin of the British Trias. He had beenappointed Secretary of a British Association Committee chargedwith this work, and was making his way to Biskra when anunfortunate accid ent happened to the train by which he travelled,resulting in his sad death. It was just before his departure forAlgiers that he revised the proof of thi s account of the LongExcursion of 1908. W. W. WATTS.

The official party arrived at Oswestry on the evening of July30th, travelling from Puddington (G.W.R.) by the 2. I 5 p.m. train.Including some who joined later, about 50 members took part inthe excursions.

The headquarters were at the "Wynnstay Arms " Hotel,Oswestry, but owing to lack of accommodation some of themembers were put up at the" Queen's Hotel," Oswestry, and atother places in the town.

EXCURSION TO THE BERWYNS. 49

Friday, july 3ISt.-An early start was made for Llangollen,leaving Oswestry (G.W.R.) at 8 a.m., and this gave an oppor­tunity to visit Plas Newydd and other places of interest inLlangollen before commencing the geological work planned forthe day.

Assembling on the Dee Bridge at 10 a.m., the party walkedto Pentre-felin, about Ii miles west of the town. In a smallquarry by the roadside a considerable number of fossils werecollected, including Cardiola interrupta, crinoid stems andgraptolites, but their state of preservation did not in all casesadmit of precise determination. A discussion took place in thequarry on the stratigraphical horizon of the beds. Situated inthe centre of a great syncline of Silurian rocks extending fromGlyn Ceiriog on the south to Cyrn-y-Brain on the north, theypresumably occupy a high position in the Silurian series, and thefaunal contents as far as they could be made out were consistentwith the view that the slates are of Ludlow age.

On ascending the hill towards the Eglwyseg Escarpment,other exposures of slate were traced until the faulted junctionbetween the Silurian and Carboniferous was crossed near DinbrenDchaf.

The Basement Conglomerates and Sandstones of the Carbon­iferous series were examined in a roadside cutting near the farmof Dinbren Uchaf and then an ascent was made of the greatescarpment. The Lower Brown Limestone crops out innumerous cliff projections from the screes and was found tocontain large quantities of the characteristic fossil Daviesiella(productus) llangollensis.

Above this a great scar of white limestone succeeds, the topof which marks the limits of the lower and upper parts of theDibunophyllum-zone (D, and Ds- ). The party stopped for luncheonon the dividing line between the two sub-zones, and advantage wastaken of the extensive view which the eminence affords to becomeacquainted with the general features of the landscape. On the eaststretches the Triassic plain of Cheshire, its low and level surfacebroken only by the Keuper escarpments of Beeston and Peckforton.To the south the conical hill of Castell Dinas Bran is separatedfrom our standpoint on the escarpment by a narrow gorge 600 ft.deep, while beyond the castle we view the long line of Silurianhills which form the northerly rim of the Berwyns. Turningtowards the west the River Dee winds like a ribbon throughsteep and wooded slopes, and on the western horizon the Arenigsfill in the notch of the valley. Towards the north-west theOrdovician rocks of Cyrn-y-Brain form lofty hills approaching1,900 ft. in height, and at their foot the Eglwyseg River, rising inthe World's End, has cut a deep gorge.

Towards the south-east, and about three miles distant, thelimestone quarries of Fron-y-Cysyllte are seen, and as a measurePROC. GEOL. Assoc., VOL. XXI, PART I, 1909.J 4

50 EXCURSION TO THE BERWYNS.

of the rapid thinning of the Carboniferous towards the south wenote that 600 ft. of the lower limestones beneath our feet are notrepresented on the opposing slopes across the valley.

From our coign of vantage the glacial features of the districtcan be seen with remarkable facility. We can follow the trackof the Dee Valley glacier all the way from its origin in theArenigs to its termination in the Eastern plain. Its course ismarked by a valley within a valley. One, the pre-Glacial, slopesgently from the hills, the other forms a U-shaped notch in thelower part. Across the mouth of the valley where the Dee entersthe plain, the great ice stream from the north flowed, and a loftymoraine is now to be seen near the railway viaduct which spansthe valley.

After lunch the party continued in an easterly course alongthe escarpment, and as the limestone dips in the same directionnewer beds came within the range of observation. At last thelimestone gave place gradually to more arenaceous varieties andthe contained fossils were distinctive of a higher zone (D 3. ) .

A descent was now made down one of the ravines to themassive white limestone, and the extensive quarries formerlyworked along the face of the Trevor rocks gave good oppor­tunities for fossil collecting. At one place the limestone wasinterrupted for a distance of several yards and the space wasfilled with a curious mass of clay and shaly fragments. Theshales were in small, flat, oval or rounded pieces about i inch indiameter, and were of a green or reddish colour. Considerablediscussion took place as to the origin of the deposit, and in theend it was generally conceded that we were dealing with theinfilling of a swallow hole, but no one could even guess the ageand the origin of the infilling material. No rocks are known inthe neighbourhood which could yield such fragments. Thejourney was continued towards Cefn-y-Fedw and Trevor, and theCarboniferous series between the Mountain Limestone and theCoal Measures was examined.

Tea was provided at the "Australian Arms," Trevor, andsufficient time was found to visit a fine section of Coal MeasureShales in brick works near the station.

Saturday, August ISt.-Carriages left the" Wynnstay Arms"at 9. I 5 a.m, for Selattyn. Passing Brongyntyn Park the Glacialmounds of Old Oswestry and the surrounding fields were noticed,and the undulating character of the country showed the irregularmanner in which the ice laid down its burden of gravels andsands on the flanks of the hills.

After passing through the village of Selattyn the carriageswere left and a detour was made across the deep ravine of theMorla's River to a quarry on the roadside north of the stream.Here the beds consisted of bedded cherts overlain by brecciaand containing a sparse fauna of D, age. The rocks were

EXCURSION TO THE BERWYNS. 51

strongly impregnated with secondary silica. So firmly were thepebbles in the breccia held by the siliceous matrix that fracturescaused by earth stresses split across the included fragments. Asthe broken surfaces were covered by secondary silica it was con­cluded that open joints had been produced which admitted ofthe percolation of siliceous waters. An attempt was made todetermine the immediate cause of the jointing. A small fault,running at right angles to the lines of fracture, seemed to havepuckered the beds into an anticline, and this must necessarilyresult in a state of tension being produced in the uppermostlayers. In any case the order of events leading up to the jointingwas clearly established. First the deposition of siliceous gravelsin a calcareous matrix, then a replacement of the calcareousmaterial by silica and the formation of chert, then local faultingand the production of open joints, and finally a continuation ofsiliceous deposition in the spaces left after jointing.

On recrossing the valley, the limestone quarries of Craignantwere visited. The palaeontological horizon of the beds is im­mediately below the chert beds just described and has beenassigned to Do. In the south quarry a fine colony of Lithostrotionirregulare is exposed on the working face. The north quarry,near Offa's Dyke, is more extensive. Here the problemto be discussed was the origin of the great marl band,15ft. thick, intercalated with the limestone beds. Its occurrenceis by no means local, as it is found at the same horizon inquarries as far distant from each other as Bron-y-Garth andLlawnt. Is it a product of pre-existing limestones from whichthe calcareous elements have been removed by solution, or was itdeposited as a marl? If the latter, what were the conditionsexisting in the Carboniferous Seas which determined the depo­sition of marl in the anticlinal areas about Craignant, whileordinary white limestone with only thin marls was being formedat the same time in the synclinal areas to the north of Llangollenand to the south at Llanymynech?

The fauna of the marl is peculiar to itself, and althoughcalcareous nodules are numerous, they differ in structure fromthe surrounding limestone. They are true concretions andcannot be regarded as pieces of limestone which have escapeddestruction. As favouring the second view, it must be remem­bered that the beds are not far removed from the base of theCarboniferous as developed in the area, and during their depositionthe land was sinking. Hence we have favourable conditions forthe laying down of beds of variable composition. With rapiddepression, deep and clear water facies would be produced, andwhen the sinking was interrupted, deposits suitable to the con­ditions then existing would be laid down in the shallow andmuddy waters.

The carriages met the party again at the summit of the road

EXCURSION TO THE BERWYNS.

which crosses the divide between the Dee and the Severndrainage-areas. Before descending into the Ceiriog Valley, a swampydepression which cuts through the watershed at an elevation ofI, I 50 ft. was examined. It presents all the features of a glacialoverflow and might be functional if we admit that the northernice blocked up the Ceiriog Valley and impounded the watersflowing down from the west. Other notches at accordantaltitudes are found dividing the Ceiriog and Dee Valleys andthese may prove to be parts of the temporary drainage systemcaused by the presence of ice in the Cheshire Plain.

Lunch was taken at the " Glyn Valley" Hotel. Some of theparty paid a short visit to the waste heaps of the mine just behindthe hotel and were rewarded by finding a great abundance ofgraptolites in the Silurian Slates.

In the afternoon the party recrossed the Ceiriog and examinedthe fossiliferous Bala beds and the Bala Limestone on the way toDolhir.

On the top of the hill at Cae Diecws a quarry showed a fineexposure of columnar igneous rock.

From the summit a good view was obtained of Pandy Craig,where the same rock occurs, and the band could be traced formany miles as a feature in the Teirw Valley.

The igneous rock was followed down the steep slopes to theriver side, where, in a large quarry, the Cae Diecws rock is seento form the middle portion of a much wider band, whichtowards the margins takes on a fragmental character. Here thequestion arose as to the origin of the included fragments. Arethey bedded volcanic ashes or have they been produced by theshearing of an intrusive sill? The fragments include nothingwhich could not have been derived from the bed itself and theoverlying and underlying slates and limestones, and there isevidence all about that the rocks have been subject to great dis­turbances. Differences of opinion exist as to the origin of thisand other bands of igneous origin found in the neighbourhood,and the brief visit did not afford sufficient time to settle thedisputed points. About the origin of the next igneous rockvisited by the party at Hendre no differences exist. It is a greatintrusive sill of basic rock and the slates on both margins havebeen metamorphosed into spotted slates. The carriages werewaiting at Hendre and conveyed the members back to Glyn,where tea was taken, and then followed a delightful drivethrough the Ceiriog Valley to Chirk and along the foot of thehills to Oswestry,

The party left the Ceiriog Valley with regret that so few ofthe many points of interest it affords had been seen, and on theway home only a passing glance could be taken of the finesequence of Silurian and Carboniferous rocks exposed on theway to Chirk, Mention must be made of the moraines which

EXCURSION TO THE BERWYNS. 53

stretched across the valley near Pont Fadog, the beautiful riverterraces and the oxbows which indicate the former windings ofthe stream.

Monday, August Jrd.-A start was made about 9.15 a.m.for Allanson's Quarry, near the Oswestry Racecourse. Soonafter leaving the town numerous heaps of debris were seen whichindicated the positions of abandoned coal mines. Allanson'sQuarry has not been worked for many yeats, and even its positionand name have passed out of remembrance among any but theoldest of the dwellers in the neighbourhood. Its chief interestlies in the fact that in the arenaceous limestones and overlyingcherts a rich (D 3) fauna is contained corresponding in age withbeds of a similar lithological character near Craignant and Cefn­y-Fedw,

Lithologically they resemble the Pendleside series of otherlocalities in the north of England, but the following fossils foundin the quarry show that they belong to a lower horizon: Caniniacampophyllum, Actinoconchus planosulcata, Productus concinnus,etc. The party then drove across the racecourse to Gloppa,where a great mound of glacial gravel has been extensivelyquarried to provide sand for the filter beds of the Liverpool Cor­poration water supply. Beautiful sections of the false beddedsands and gravels were seen and a profusion of boulders hasbeen left as a result of screening the sand. The erratics aremostly of northern origin, but local rocks and felsites from thewest are not uncommon.

Why there should be a commingling of the two types oferratics was discussed, and from the elevation on which Gloppastands it was easy to follow the course of events which broughtthe assemblage of stones to their present position. Towards thewest the glacial deposits are composed of Welsh material only.In the plains to the east the drift-covered plain yields northernerratics with fragments of marine shells. On the flanks of thehills, sloping towards the plain, the two boulder clays are seen inconjunction. Below is a dark clay with Welsh erratics andabove it lies a reddish boulder clay with partings of sand, con­taining stones from Scotland and the Lake District and shellfragments. It was argued that the Welsh ice debouched into theplain from the west and shrunk back into the valley before thenorthern component reached the district. The latter, in itsprogress along the borders of the hills, picked up the Welsherratics and deposited them in the mounds at Gloppa, OldOswestry, and other places.

A short halt was made at Offa's Dyke, and then the partydrove to the limestone quarries at Llawnt, Here the limestoneis seen resting on shales. A short time was given to the examin­ation of the shales. They are usually regarded as of Ordovicianage, but no fossils were found which would serve to determine

54 EXCURSION TO THE BERWYNS.

their stratigraphical position. The limestones are interbeddedwith shale bands and curious effects have been produced byfaults cutting across the faces of the quarry. In one place a thinmarl band runs with the dip to a certain point, then rises almostvertically about 4 ft. across the strata and is continued along thedip on the other side. The beds, above and below, show nosigns of disturbance.

The manner in which the phenomenon had been producedwas eagerly discussed, and the suggestion which best explainedthe problem was that a wedge of limestone had been thrusthorizontally between the beds, and slickensiding along thebedding planes.

Lunch was taken at the" Cross Foxes" Inn and the journeywas continued through Llansilin to Glascoed.

The road runs for several miles along the western side of thegorge of the Cynllaith River, and this roughly divides the Carbon­iferous rocks on the east from the Ordovician slates on the west.

The picturesque escarpment of Mountain Limestone, cappedby the ruins of Coed-y-Gaer, were in full view, and great blocksof limestone which strew the slopes gave a picture of ruinousdecay.

At Glascoed hornblende andesite is worked in a quarry by theroadside. It is exposed as gigantic horizontal columns, four orfive feet thick.

The carriages were again taken on the summit of the hill, andafter passing numerous limestone quarries Trefonen was reachedand tea was provided at the Inn.

About a mile south of the village the Treflach Wood Quarrieswere entered and a walk of about half-a-mile gave very beautifulsections, and numerous corals of very large size were obta ined.

Time did not admit of a detailed examination of the NantMawr Quarries and the very fossiliferous Bala beds on which thelimestones rest. and the drive was continued across the mouth ofthe Morda defj'le and through Porth-y-Waen to Oswestry.

After dinner the Director gave an address on "The GeneralGeology of the District," and an interesting discussion followed.

Tuesday, August 4th.-Carriages left Oswestry at 9.15 a.m.for Llanrhaiadr-yn-Mochnant, For some miles the route layalong the drift covered plain at the foot of the mountains, butafter passing Llynclys the road traverses the limestone gap ofPorth-y-Waen and then opens out suddenly into the broad valleyof the Tanat. In front the Silurian and Ordovician slates rise insmooth-contoured hills often crowned by dense masses of trees,while behind, thc limestone ciiffs stand gaunt and bare. Thestriking contrasts of form enable one to trace the limits of thevarious rocks even at a distance, and from the road near Llany­blodwell the influence of the faults in displacing the escarpment

EXCURSION TO THE BERWYNS. 55

towards the east as we proceed from north to south can beclearly made out.

At Llangedwyn a short stay was made to examine the fos­siliferous slates near the Inn. Glacial mounds, stretching acrossthe valley, were pointed out at various stages of the journey,marking the halting places of the glacier which formerly floweddown from the westerly hills. Just before entering Llanrhaiadrseveral beautiful Tomens were seen on both sides of the road.

A short stay at Llanrhaiadr enabled some of the party tomake a hasty examination of the black shales exposed in thestream behind the church. No fossils have been recorded fromthese beds, although their general characters suggest that agraptolite fauna should be found in them. Their age is probablyLower Llandeilo. The drive was continued up the valley of theAfon Rhaiadr to the waterfall at the head of the valley. Lunchwas taken at the cottage at the foot of the falls, and then anexamination was made of the great pothole into which the waterfalls in its first plunge, and some of the members climbed thewooded slopes to the junction of the Felsite and underlyingslates.

Llyn-llyn-Caws was next visited: a dark and gloomy lake whichrests under the cirque of Moel Sych. The more active of theparty climbed to the summit of Cader Berwyn and were rewardedwith one of the finest and most extensive views that North Waleshas to offer.

On the homeward journey tea was provided at the" WynnstayArms," Llanrhaiadr.

Wednesday, August 5th. - The party left the CambrianStation, Oswestry, at 8.30 a.m. for Llangynog. The railwayfollows a route parallel to the drive of yesterday and the generalfeatures observed were the same as far as Llanrhaiadr. Here therailway continues along the course of the Tanat. In its upperreaches the valley becomes more contracted and shows signs ofoverdeepening by ice action, for hanging valleys are seen on theslopes on both sides. Immediately on arrival the great boss ofspherulitic Rhyolite south of Llangynog was examined. Fromthe summit of the boss a very extensive view was obtainedembracing the Penant Valley, the Pass of Milltir Gerig, CraigRhiwarth, etc.

In the afternoon the road to Milltir Gerig was followed as faras the Greenstone Dyke at Trwyn-swch, On the way twoigneous bands corresponding with those found at Glyn werecrossed and the Bala Limestone here is phosphatic.

The dyke occurs in a deep ravine, and is so much decom­posed that it was difficult to get a fresh specimen of the rock.

On returning to Llangynog along the banks of the Eiarth asmall party visited the Craig Rhiwarth Slate Quarries.

EXCURSION TO THE BERWYNS.

Tea was provided at the" New Inn," Llangynog, and thereturn journey was made by the 5.50 p.m. train.

Thursday, August 6th.-The route followed was the same asthat of Tuesday as far as Llynclys. A detour was then madethrough Llanymynech, Four Crosses and through Llansantffraid­yn-Mechain to Llanyblodwell.

This gave an opportunity of seeing the lower part of theVyrnwy Valley and the beautiful oxbows and windings of theTanat just before it enters the Vyrnwy.

The drive from Llanyblodwell was along familiar ground untilapproaching Llanrhaiadr. Thence a circuitous road was takento Craig-y-Olyn. The long drive of the morning left all too littletime to complete the day's programme, so the larger portion ofthe party remained to collect in the Llandeilo limestones while afew visited the Maen Gwynedd Slate Mine on Cader Berwyn.Through the kindness of Mr. D. Davies, the proprietor, theunderground workings were examined and an al fresco tea wasprovided at one of the workmen's cottages.

Friday, August 7th.-The object of the day's work was tomake a complete traverse of the Carboniferous succession. Incrossing Sweeney Mountain to Porth-y-Waen good sections wereexposed in roadside cuttings and in quarries. At the summit ofthe mountain the President gave an interesting account of thegeology of the Breidden Hills which were in full view.

At Llanyblodwell a quarry in igneous rock was examined. Itconsists of a hornblendic andesite and curious quartz veins runthrough the mass. The veins are clear on the outside and milkytowards the centre. While lunch was being eaten a discussiontook place as to the origin of these veins.

In another quarry to the south Glacial deposits were seen tooverlie the igneous rock, and where the surface was freshlyexposed the latter showed Glacial strire. The summit of Llany­mynech Hill was next attained, from which a very beautiful viewwas obtained, including the Breiddens and the Severn Valley inthe foreground, Longmynd and the Wrekin towards the southand south-east, while to the north and west most of the groundvisited during the excursion was in view, and from this pointmany of the observations which had been made could be sum­marised and put in their proper perspective.

After tea at the" Lion" Hotel votes of thanks were passed tothe Director and Excursion Secretary for the services renderedduring the week. Returning to Oswestry by train there wastime to visit the Liverpool Corporation filter beds, a shortdistance north of the town.