EXCURSION TO THE BERWYNS.

had travelled from the coast to do so and had to return that evening. Mr. Wilson, having expressed his great pleasure in meeting the Association, the party then proceeded to Lower Halling, which was reached in good time for tea, which was served in an admirable manner, amid pleasant surroundings, by Mrs. Brigden at the Manor H ouse. After the usual votes of thank s, the members left Halling by the 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 following account as it was completed by Mr. Lomas only a few weeks before his untimely death. Those who took part in the Berwyn Excursion will long remember it as one of the most pleasant and instru ctive that the Association has carried out, and not a little of the pleasure was due to the good temper and kindliness, the energy and enthusiasm, of the Leader, who had sacrificed no small fraction of his holiday in order to conduct the excursion. Mr. Lomas had arranged to visit Algiers in the Christmas Vacation in order to investigate there certain phenomena which promised to throw some new light on a subject always of great interest to him--the origin of the British Trias. He had been appointed Secretary of a British Association Committee charged with this work, and was making his way to Biskra when an unfortunate accid ent happened to the train by which he travelled, resulting in his sad death. It was just before his departure for Algiers that he revised the proof of this account of the Long Excursion of 1908. W. W. WATTS.

The official party arrived at Oswestry on the evening of July 30th, travelling from Puddington (G.W.R.) by the 2. I 5 p.m. train. Including some who joined later, about 50 members took part in the excursions. The headquarters were at the "Wynnstay Arms " Hotel, Oswestry, but owing to lack of accommodation some of the members were put up at the" Queen's Hotel," Oswestry, and at other 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 oppor­ tunity to visit Plas Newydd and other places of interest in Llangollen before commencing the geological work planned for the day. Assembling on the Dee Bridge at 10 a.m., the party walked to Pentre-felin, about Ii miles west of the town. In a small quarry by the roadside a considerable number of fossils were collected, including Cardiola interrupta, crinoid stems and graptolites, but their state of preservation did not in all cases admit of precise determination. A discussion took place in the quarry on the stratigraphical horizon of the beds. Situated in the centre of a great syncline of Silurian rocks extending from Glyn Ceiriog on the south to Cyrn-y-Brain on the north, they presumably occupy a high position in the Silurian series, and the faunal contents as far as they could be made out were consistent with 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 junction between the Silurian and Carboniferous was crossed near Dinbren Dchaf. The Basement Conglomerates and Sandstones of the Carbon­ iferous series were examined in a roadside cutting near the farm of Dinbren Uchaf and then an ascent was made of the great escarpment. The Lower Brown Limestone crops out in numerous cliff projections from the screes and was found to contain large quantities of the characteristic fossil Daviesiella (productus) llangollensis. Above this a great scar of white limestone succeeds, the top of which marks the limits of the lower and upper parts of the Dibunophyllum-zone (D, andDs- ). The party stopped for luncheon on the dividing line between the two sub-zones, and advantage was taken of the extensive view which the eminence affords to become acquainted with the general features of the landscape. On the east stretches the Triassic plain of Cheshire, its low and level surface broken only by the Keuper escarpments of Beeston and Peckforton. To the south the conical hill of Castell Dinas Bran is separated from our standpoint on the escarpment by a narrow gorge 600 ft. deep, while beyond the castle we view the long line of Silurian hills which form the northerly rim of the Berwyns. Turning towards the west the River Dee winds like a ribbon through steep and wooded slopes, and on the western horizon the Arenigs fill in the notch of the valley. Towards the north-west the Ordovician rocks of Cyrn-y-Brain form lofty hills approaching 1,900 ft. in height, and at their foot the Eglwyseg River, rising in the World's End, has cut a deep gorge. Towards the south-east, and about three miles distant, the limestone quarries of Fron-y-Cysyllte are seen, and as a measure PROC. GEOL. Assoc., VOL. XXI, PART I, 1909.J 4 50 EXCURSION TO THE BERWYNS.

of the rapid thinning of the Carboniferous towards the south we note that 600 ft. of the lower limestones beneath our feet are not represented on the opposing slopes across the valley. From our coign of vantage the glacial features of the district can be seen with remarkable facility. We can follow the track of the Dee Valley glacier all the way from its origin in the Arenigs to its termination in the Eastern plain. Its course is marked by a valley within a valley. One, the pre-Glacial, slopes gently from the hills, the other forms a U-shaped notch in the lower part. Across the mouth of the valley where the Dee enters the plain, the great ice stream from the north flowed, and a lofty moraine is now to be seen near the railway viaduct which spans the valley. After lunch the party continued in an easterly course along the escarpment, and as the limestone dips in the same direction newer beds came within the range of observation. At last the limestone gave place gradually to more arenaceous varieties and .). the contained fossils were distinctive of a higher zone (D 3 A descent was now made down one of the ravines to the massive white limestone, and the extensive quarries formerly worked along the face of the Trevor rocks gave good oppor­ tunities for fossil collecting. At one place the limestone was interrupted for a distance of several yards and the space was filled with a curious mass of clay and shaly fragments. The shales were in small, flat, oval or rounded pieces about i inch in diameter, and were of a green or reddish colour. Considerable discussion took place as to the origin of the deposit, and in the end it was generally conceded that we were dealing with the infilling of a swallow hole, but no one could even guess the age and the origin of the infilling material. No rocks are known in the neighbourhood which could yield such fragments. The journey was continued towards Cefn-y-Fedw and Trevor, and the Carboniferous series between the Mountain Limestone and the Coal Measures was examined. Tea was provided at the "Australian Arms," Trevor, and sufficient time was found to visit a fine section of Coal Measure Shales 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 Glacial mounds of Old Oswestry and the surrounding fields were noticed, and the undulating character of the country showed the irregular manner in which the ice laid down its burden of gravels and sands on the flanks of the hills. After passing through the village of Selattyn the carriages were left and a detour was made across the deep ravine of the Morla's River to a quarry on the roadside north of the stream. Here the beds consisted of bedded cherts overlain by breccia and containing a sparse fauna of D, age. The rocks were EXCURSION TO THE BERWYNS. 51 strongly impregnated with secondary silica. So firmly were the pebbles in the breccia held by the siliceous matrix that fractures caused by earth stresses split across the included fragments. As the broken surfaces were covered by secondary silica it was con­ cluded that open joints had been produced which admitted of the percolation of siliceous waters. An attempt was made to determine the immediate cause of the jointing. A small fault, running at right angles to the lines of fracture, seemed to have puckered the beds into an anticline, and this must necessarily result in a state of tension being produced in the uppermost layers. In any case the order of events leading up to the jointing was clearly established. First the deposition of siliceous gravels in a calcareous matrix, then a replacement of the calcareous material by silica and the formation of chert, then local faulting and the production of open joints, and finally a continuation of siliceous deposition in the spaces left after jointing. On recrossing the valley, the limestone quarries of Craignant were visited. The palaeontological horizon of the beds is im­ mediately below the chert beds just described and has been assigned to Do. In the south quarry a fine colony of Lithostrotion irregulare is exposed on the working face. The north quarry, near Offa's Dyke, is more extensive. Here the problem to be discussed was the origin of the great marl band, 15ft. thick, intercalated with the limestone beds. Its occurrence is by no means local, as it is found at the same horizon in quarries as far distant from each other as Bron-y-Garth and Llawnt. Is it a product of pre-existing limestones from which the calcareous elements have been removed by solution, or was it deposited as a marl? If the latter, what were the conditions existing in the Carboniferous Seas which determined the depo­ sition of marl in the anticlinal areas about Craignant, while ordinary white limestone with only thin marls was being formed at the same time in the synclinal areas to the north of Llangollen and to the south at Llanymynech? The fauna of the marl is peculiar to itself, and although calcareous nodules are numerous, they differ in structure from the surrounding limestone. They are true concretions and cannot be regarded as pieces of limestone which have escaped destruction. As favouring the second view, it must be remem­ bered that the beds are not far removed from the base of the Carboniferous as developed in the area, and during their deposition the land was sinking. Hence we have favourable conditions for the laying down of beds of variable composition. With rapid depression, deep and clear water facies would be produced, and when the sinking was interrupted, deposits suitable to the con­ ditions then existing would be laid down in the shallow and muddy 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 Severn drainage-areas. Before descending into the Ceiriog Valley, a swampy depression which cuts through the watershed at an elevation of I, I 50 ft. was examined. It presents all the features of a glacial overflow and might be functional if we admit that the northern ice blocked up the Ceiriog Valley and impounded the waters flowing down from the west. Other notches at accordant altitudes are found dividing the Ceiriog and Dee Valleys and these may prove to be parts of the temporary drainage system caused by the presence of ice in the Cheshire Plain. Lunch was taken at the " Glyn Valley" Hotel. Some of the party paid a short visit to the waste heaps of the mine just behind the hotel and were rewarded by finding a great abundance of graptolites in the Silurian Slates. In the afternoon the party recrossed the Ceiriog and examined the fossiliferous Bala beds and the Bala Limestone on the way to Dolhir. On the top of the hill at Cae Diecws a quarry showed a fine exposure 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 for many miles as a feature in the Teirw Valley. The igneous rock was followed down the steep slopes to the river side, where, in a large quarry, the Cae Diecws rock is seen to form the middle portion of a much wider band, which towards the margins takes on a fragmental character. Here the question arose as to the origin of the included fragments. Are they bedded volcanic ashes or have they been produced by the shearing of an intrusive sill? The fragments include nothing which could not have been derived from the bed itself and the overlying and underlying slates and limestones, and there is evidence all about that the rocks have been subject to great dis­ turbances. Differences of opinion exist as to the origin of this and other bands of igneous origin found in the neighbourhood, and the brief visit did not afford sufficient time to settle the disputed points. About the origin of the next igneous rock visited by the party at Hendre no differences exist. It is a great intrusive sill of basic rock and the slates on both margins have been metamorphosed into spotted slates. The carriages were waiting at Hendre and conveyed the members back to Glyn, where tea was taken, and then followed a delightful drive through the Ceiriog Valley to Chirk and along the foot of the hills to Oswestry, The party left the Ceiriog Valley with regret that so few of the many points of interest it affords had been seen, and on the way home only a passing glance could be taken of the fine sequence of Silurian and Carboniferous rocks exposed on the way to Chirk, Mention must be made of the moraines which EXCURSION TO THE BERWYNS. 53 stretched across the valley near Pont Fadog, the beautiful river terraces and the oxbows which indicate the former windings of the stream. Monday, August Jrd.-A start was made about 9.15 a.m. for Allanson's Quarry, near the Oswestry Racecourse. Soon after leaving the town numerous heaps of debris were seen which indicated the positions of abandoned coal mines. Allanson's Quarry has not been worked for many yeats, and even its position and name have passed out of remembrance among any but the oldest of the dwellers in the neighbourhood. Its chief interest lies in the fact that in the arenaceous limestones and overlying cherts a rich (D 3) fauna is contained corresponding in age with beds of a similar lithological character near Craignant and Cefn­ y-Fedw, Lithologically they resemble the Pendleside series of other localities in the north of England, but the following fossils found in the quarry show that they belong to a lower horizon: Caninia campophyllum, Actinoconchus planosulcata, Productus concinnus, etc. The party then drove across the racecourse to Gloppa, where a great mound of glacial gravel has been extensively quarried to provide sand for the filter beds of the Liverpool Cor­ poration water supply. Beautiful sections of the false bedded sands and gravels were seen and a profusion of boulders has been left as a result of screening the sand. The erratics are mostly of northern origin, but local rocks and felsites from the west are not uncommon. Why there should be a commingling of the two types of erratics was discussed, and from the elevation on which Gloppa stands it was easy to follow the course of events which brought the assemblage of stones to their present position. Towards the west the glacial deposits are composed of Welsh material only. In the plains to the east the drift-covered plain yields northern erratics with fragments of marine shells. On the flanks of the hills, sloping towards the plain, the two boulder clays are seen in conjunction. Below is a dark clay with Welsh erratics and above it lies a reddish boulder clay with partings of sand, con­ taining stones from Scotland and the Lake District and shell fragments. It was argued that the Welsh ice debouched into the plain from the west and shrunk back into the valley before the northern component reached the district. The latter, in its progress along the borders of the hills, picked up the Welsh erratics and deposited them in the mounds at Gloppa, Old Oswestry, and other places. A short halt was made at Offa's Dyke, and then the party drove to the limestone quarries at Llawnt, Here the limestone is seen resting on shales. A short time was given to the examin­ ation of the shales. They are usually regarded as of Ordovician age, but no fossils were found which would serve to determine 54 EXCURSION TO THE BERWYNS. their stratigraphical position. The limestones are interbedded with shale bands and curious effects have been produced by faults cutting across the faces of the quarry. In one place a thin marl band runs with the dip to a certain point, then rises almost vertically about 4 ft. across the strata and is continued along the dip on the other side. The beds, above and below, show no signs of disturbance. The manner in which the phenomenon had been produced was eagerly discussed, and the suggestion which best explained the problem was that a wedge of limestone had been thrust horizontally between the beds, and slickensiding along the bedding planes. Lunch was taken at the" Cross Foxes" Inn and the journey was continued through Llansilin to Glascoed. The road runs for several miles along the western side of the gorge of the Cynllaith River, and this roughly divides the Carbon­ iferous rocks on the east from the Ordovician slates on the west. The picturesque escarpment of Mountain Limestone, capped by the ruins of Coed-y-Gaer, were in full view, and great blocks of limestone which strew the slopes gave a picture of ruinous decay. At Glascoed hornblende andesite is worked in a quarry by the roadside. It is exposed as gigantic horizontal columns, four or five feet thick. The carriages were again taken on the summit of the hill, and after passing numerous limestone quarries Trefonen was reached and tea was provided at the Inn. About a mile south of the village the Treflach Wood Quarries were entered and a walk of about half-a-mile gave very beautiful sections, and numerous corals of very large size were obta ined. Time did not admit of a detailed examination of the Nant Mawr Quarries and the very fossiliferous Bala beds on which the limestones rest. and the drive was continued across the mouth of the Morda defj'le and through Porth-y-Waen to Oswestry. After dinner the Director gave an address on "The General Geology 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 lay along the drift covered plain at the foot of the mountains, but after passing Llynclys the road traverses the limestone gap of Porth-y-Waen and then opens out suddenly into the broad valley of the Tanat. In front the Silurian and Ordovician slates rise in smooth-contoured hills often crowned by dense masses of trees, while behind, thc limestone ciiffs stand gaunt and bare. The striking contrasts of form enable one to trace the limits of the various rocks even at a distance, and from the road near Llany­ blodwell 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 be clearly made out. At Llangedwyn a short stay was made to examine the fos­ siliferous slates near the Inn. Glacial mounds, stretching across the valley, were pointed out at various stages of the journey, marking the halting places of the glacier which formerly flowed down from the westerly hills. Just before entering Llanrhaiadr several beautiful Tomens were seen on both sides of the road. A short stay at Llanrhaiadr enabled some of the party to make a hasty examination of the black shales exposed in the stream behind the church. No fossils have been recorded from these beds, although their general characters suggest that a graptolite fauna should be found in them. Their age is probably Lower Llandeilo. The drive was continued up the valley of the Afon Rhaiadr to the waterfall at the head of the valley. Lunch was taken at the cottage at the foot of the falls, and then an examination was made of the great pothole into which the water falls in its first plunge, and some of the members climbed the wooded slopes to the junction of the Felsite and underlying slates. Llyn-llyn-Caws was next visited: a dark and gloomy lake which rests under the cirque of Moel Sych. The more active of the party climbed to the summit of Cader Berwyn and were rewarded with one of the finest and most extensive views that North Wales has to offer. On the homeward journey tea was provided at the" Wynnstay Arms," Llanrhaiadr. Wednesday, August 5th. - The party left the Cambrian Station, Oswestry, at 8.30 a.m. for Llangynog. The railway follows a route parallel to the drive of yesterday and the general features observed were the same as far as Llanrhaiadr. Here the railway continues along the course of the Tanat. In its upper reaches the valley becomes more contracted and shows signs of overdeepening by ice action, for hanging valleys are seen on the slopes on both sides. Immediately on arrival the great boss of spherulitic Rhyolite south of Llangynog was examined. From the summit of the boss a very extensive view was obtained embracing the Penant Valley, the Pass of Milltir Gerig, Craig Rhiwarth, etc. In the afternoon the road to Milltir Gerig was followed as far as the Greenstone Dyke at Trwyn-swch, On the way two igneous bands corresponding with those found at Glyn were crossed and the Bala Limestone here is phosphatic. The dyke occurs in a deep ravine, and is so much decom­ posed that it was difficult to get a fresh specimen of the rock. On returning to Llangynog along the banks of the Eiarth a small party visited the Craig Rhiwarth Slate Quarries. EXCURSION TO THE BERWYNS.

Tea was provided at the" New Inn," Llangynog, and the return journey was made by the 5.50 p.m. train. Thursday, August 6th.-The route followed was the same as that of Tuesday as far as Llynclys. A detour was then made through Llanymynech, Four Crosses and through Llansantffraid­ yn-Mechain to Llanyblodwell. This gave an opportunity of seeing the lower part of the Vyrnwy Valley and the beautiful oxbows and windings of the Tanat just before it enters the Vyrnwy. The drive from Llanyblodwell was along familiar ground until approaching Llanrhaiadr. Thence a circuitous road was taken to Craig-y-Olyn. The long drive of the morning left all too little time to complete the day's programme, so the larger portion of the party remained to collect in the Llandeilo limestones while a few visited the Maen Gwynedd Slate Mine on Cader Berwyn. Through the kindness of Mr. D. Davies, the proprietor, the underground workings were examined and an al fresco tea was provided at one of the workmen's cottages. Friday, August 7th.-The object of the day's work was to make a complete traverse of the Carboniferous succession. In crossing Sweeney Mountain to Porth-y-Waen good sections were exposed in roadside cuttings and in quarries. At the summit of the mountain the President gave an interesting account of the geology of the Breidden Hills which were in full view. At Llanyblodwell a quarry in igneous rock was examined. It consists of a hornblendic andesite and curious quartz veins run through the mass. The veins are clear on the outside and milky towards the centre. While lunch was being eaten a discussion took place as to the origin of these veins. In another quarry to the south Glacial deposits were seen to overlie the igneous rock, and where the surface was freshly exposed the latter showed Glacial strire. The summit of Llany­ mynech Hill was next attained, from which a very beautiful view was obtained, including the Breiddens and the Severn Valley in the foreground, Longmynd and the Wrekin towards the south and south-east, while to the north and west most of the ground visited during the excursion was in view, and from this point many of the observations which had been made could be sum­ marised and put in their proper perspective. After tea at the" Lion" Hotel votes of thanks were passed to the Director and Excursion Secretary for the services rendered during the week. Returning to Oswestry by train there was time to visit the Liverpool Corporation filter beds, a short distance north of the town.