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large subnodular masses in the line of the strike of the upper slaty beds. This brings us to a fault near the river Elan above the dam at Caban Côch, and to the blue argillaceous and arenaceous slates of Cefn craig-y-Foel, thence across the river Elan a second time, continued along this section over Tyn-y-faen, Bryn-ygwal, Nant Brythgwm, Esgair gris, near Lluest Abercaethon, Clawdd du mawr, Esgair Cormwg, Banc-trappau-Dwrgwn, Esgair Llwyd, Disputed ground, Trisny-gwr, Bwrllwmau Elan, and Cefn-banc-hir close to the sources of the rivers Elan and Claerwen. These Caradoc or Bala and Lower Llandovery rocks, consisting of shales banded with thin sandstones, with thick beds of coarse sandstone, and conglomerates, some of the beds covered with tracks of Annelida, are continued hence onwards for the next 17 miles or more as far as Cardigan Bay.

In 1879 Professor Lapworth gave the title "Ordovician" to this series, a very appropriate name from its continuity over the territory of the Ordovices.

The only reference to this district which I can find in Woodward's "Geology of England and Wales," 2nd edition, 1887, is on page 92, where he writes: "Above the Cardiganshire group (Metalliferous-slate group, 2,000 feet, and Aberystwith grits of Sedgwick 1,000 feet), come the Plynlimmon grits, 1,000 feet, forming a line of high country in the centre of Wales, including Plynlimmon. These grits are probably an arenaceous development of the Tarannon Shales, and the Cwm-Elan conglomerates and Rhayader Pale Slates belong to the same series."

The fault above referred to lies between Tan-y-Foel and Caban Côch Dam, and follows the line of the streamlet which discharges into the Elan just below Tan-y-Foel, passing almost under the shop, previously mentioned, at Abernant stores. It crosses the Tunnel aqueduct about 900 yards from its eastern extremity, its direction being N.N.E. to S.S. W. by W., to the river Elan about 200 or 300 yards west of the Caban Côch Dam; thence down the valley along the course of the river Elan for about a mile. The fault is not observeable to any extent upon the right bank. Professor Green and Mr. Topley discovered signs of it again on the left bank of the Claerwen above Aber Elan, where it re-appears under the tennis court at Nantgwyllt. A little higher up the river Claerwen are several faults which may be in continuity thereof.

Immediately above Abernant, the bedding planes of the grits and slates are almost vertical, and exhibit many contortions and curious foldings, but in order to properly inspect them a good deal of stiff climbing is necessary. Mr. Eustace Tickell, engineer in charge of the Pen-y-gang Dam, informs me that the most marvellous instances of contortion within his knowledge are to be seen in the bed of the Claerwen near Cwm Clyd, above half a mile above the Rhiwnant stream, and near an old lead mine.

Mr. Tickell has called my attention to an interesting exposure on the right bank of Nant-y-gro, above the Mason's yard on the right bank of the Elan, where the temporary railway has been cut on the hill side. He writes:-“The trend of the hill side is here nearly at right angles to the cleavage, and the slopes have been rounded into smooth curves by the passage of ice. In the cutting referred to the edges of the slates can be seen bent backwards in the direction of the

glacier, and in some places I have found a striated boulder of grit imbedded in the crushed slate."

A fine example of a small terminal moraine may be seen on the Claerwen, nearly opposite Nant-y-Gader. It is clearly shown on the map in Mr. Tickells' charmingly illustrated book, "The Vale of Nantgwyllt" (Virtue & Co., 1894), by a sharp indentation of the top water contour of Cil-Oerwynt Reservoir near its upper end. Mr. Tickell informs me that the rocks in this neighbourhood are much striated, and he strongly recommends the Claerwen Valley in preference to the Elan from a naturalists' point of view, the geology being much more varied, and the birds have not been disturbed as in the Elan Valley, where the Water Supply Works now exert a preponderating influence.

In "Records of the Rocks," Mr. Symonds expresses his belief, on page 136, that there is a trap dyke running from the Drygan, a hill 2,120 feet high, close to the source of the Rhiwnant, across the hills to Cefn Craig-y-foel, which disturbs the strata, and that lead ore occurs thinly along its strike. As regards the lead ore, there is a disused mine up the valley beyond Cwm Elan. And at the present time lead ore is being extracted from the mines at Nant-y-carw up the Claerwen Valley. There used to be lead mines at Craig Rhiwnant and at Craig Dalrhiw on each bank of the river Rhiwnant which falls into the Claerwen half a mile west of Dol-y-Mynach.

You will have observed when we were at the Dam at Caban Côch the mixture of extremely hard conglomerates and grits of the Lower Silurian series, on the south, or Breconshire side of the river. Again you will have noticed the closely grained texture of the rock on the north side of the Dam, in Radnorshire, from which quarry the best stone is obtained for its construction. In this quarry is a vein of quartz six feet in thickness. At Careg-Ddu, where we now stand, the Pot-holes in the bed of the river indicate the homogeneity of the rock in this locality, and the excavation which you have crossed shows an exposure of excellently hard blue slate in many places of large extent, and free from splitting. In fact, if the bed of the river and southern extremity at Caban Côch had been similarly free from cracks, we should have found much more progress made with the excavations at that locality.

As regards fossils you will not expect to find many of them in these palaeozoic rocks-nothing probably beyond traces of Annelida, soft-bodied animals which are seldom preserved in a fossil state, such as earthworms, sandworms, tubeworms, &c. and occasionally a few Graptolites of the division of Hydrozoa which present a pleasing variety of form, and which range from the base of the Ordovician system to the summit of the Silurian series. This Ordovician system demonstrates the period of culmination of the Graptolites.

Here we now see man busy making this extensive excavation in hard slaty rock with machinery and tools of the latest up to date pattern, yet how insignificant is his work compared with the upheavals, deposits, erosions, and denudation of æons of the work of Nature, with her tools of wind, rain, frost, snow, ice wedges, alternations of heat and cold, streams, rivers, and glaciers. Even to day Nature holds no armistice: this shower of rain is carrying material down the

river past Hereford into the Bristol Channel.

That the configuration of the remarkable and extensive basin of this catchment is due to glacier action and denudation from the effects of ice, frost, and rain, is evident. Proceed four miles higher up the course of the river and you will find yourself in the hollow of an extensive basin with a diameter of three miles, the barrier of which in the west is the elevated and rounded plateau which separates the Elan from the Claerwen, and constitutes their watershed. See the plan presented to you. Where we now stand, with this forbidding rampart of shattered slaty rock within our reach, is a valley connecting two of the smaller enclosed basins.

The remarkable erosive power of water is exhihited not only in the Pot-holes below us, but in the narrow clefts in solid rocks as you proceed up the course of the Elan, especially marked at Pont-yr-hyllfan (the bridge of the awful place) and in numerons other localities. At Pont-yr-hyllfan the channel has become so narrowed by erosion that it is difficult for any one to believe that a horse could possibly have been carried by the current through so narrow a chasm,-a fact which has occurred. Another curious testimony of the power of water is exhibited at that locality-just above the single baulk which spans the river there-the stony bed of the river is dry for a length of about twenty yards, a subterranean passage having been excavated by hydrodynamic pressure, aided by stones set revolving as it were by a drilling machine in the cavity: moreover there is another cavity, oblique to the watercourse, the extremity of which cannot be reached by a twenty-feet pole.

For evidence of detritus and moraines brought down by torrents and glacier action, look at that clay-like surface soil opposite, overlying the rocks which recently covered these excavations at Careg-Ddu: as you follow it higher up the hill the deposit attains a depth of fifteen to twenty feet. Observe here and there a boulder peeping out of the deposit. If you will go a little higher up the hill you will find that a heap of fifty to a hundred boulders met with in this excavation have been stacked together. These boulders are of grit, and have come down from the beds in Nant Hirin which empties into the Elan nine miles distant, or about a mile and a half beyond Pont-ar-Elan. If you examine them you will find striations marked upon them; in some cases their surfaces are quite polished, due to friction under an enormous weight of travelling frozen snow. The average size of the boulders in this collection is about that of a four-and-a-half-gallon barrel.

The two rivers Elan and Claerwen both have their source from the high moorland east of Cefn Banc Hir, near which is a place marked on the Ordnance Map as Geifas, close to a triangular station with an elevation of 1,873 feet. The Elan takes a circuitous north-easterly course, and the Claerwen takes a southeasterly circuit, the rivers maintaining a distance apart of from three to five miles for more than half their course before their junction at Aber Elan; the length of the Elan before its union being 12 miles, and that of the Claerwen 12 miles. These rivers are computed to supply between one-sixth and one-seventh of the water passing through Hereford, and that the very best. The purity of the water is established by reason of its freedom from pollution by manured land or sewage from villages, the whole population of the area not exceeding 180, and the sheep

averaging 1 to the acre. The softness of the water is a great recommendation, not only for its saponifying quality, but also for its power of diminishing scaling in boilers. The Birmingham Corporation have purchased manorial rights over the area, thereby securing control over the few lead mines in the Claerwen district, with which area, however, there will be no necessity to interfere for several years hence. The city of Birmingham is fortunate in having acquired for their water supply a watershed peculiarly adapted by nature for their demands; in truth, an ideal and extensive catchment area.

The daily compensation supply of 27 million gallons will be determined by a gauge to be fixed within 300 yards of the Dam at Caban Côch. It is not anticipated that the city of Hereford will be otherwise than benefited, when it is known that during the year 1894 the daily average flow of the river Elan near Caban Côch was calculated at twelve million gallons. We learn from an article in the Hereford Times of January 9th, 1892, that during the winter month of December, 1891, the consumption of water in Hereford was 25,200,000 gallons, of which the railway companies took 24 million gallons, and the brewers and maltsters a few hundred thousand gallons. Probably the consumption will increase yearly with an increased population, nevertheless, upon the present statistics, 650,000 gallons may be considered a fair daily average.

Moreover, the Wye will be exempt from the floods which have sometimes caused both alarm and damage. The interests of the Salmon Fisheries have also been favourably considered, and the beneficial cleansing of the river by artificial spates has been guaranteed by a provision in the Bill that one-fifth of the 27 million gallons daily compensation shall be occasionally reserved each day for a fortnight, and discharged during forty-eight hours together with the daily allowance.

I must call your attention to some instructive letters which have recently appeared in the Hereford Times from Mr. John Lloyd on the subject of "The Welsh Water Scheme for London " in the issues of March 14th, 21st, 28th, and April 4th, also a further series on "The distinguishing features of the Wye and the Usk," see May 2nd and May 9th, 1896. In the Transactions of our Club, 1869, page 151, are some particulars of the daily flow of the river Wye under the bridge at Hereford, compiled by a member of our Club, Mr. Curley, C.E., then City Surveyor, from which Mr. John Lloyd has computed the number of millions of gallons in 24 hours, which table is here reproduced for the information of our City authorities, whom we have been glad to welcome in our outing to day.

TABLE SHOWING THE DAILY FLOW OF THE RIVER WYE UNDER THE BRIDGE AT

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When the river is above 10 feet high it spreads over the banks, and measurements of its flow cannot be reliably determined.

A few words should be said about the rainfall here. The annual rainfall in Herefordshire averages now throughout the county from 25 to 30 inches, whilst the average rainfall here is 68 inches. Why this difference? We have a long elevated hilly region in Wales running parallel with our western coast from St. David's Head by the heights of Plynlimmon 2,481 feet, Snowdon 3,571 feet, thence onward across the Menai Straits to Anglesea. If you will ascend on a clear day one of those heights near our present locale, you will see a continuous succession of billowy elevations on the horizon as spurs of the higher mountains on this their eastern side. The Welsh call these spurs "esgairs," from the name signifying a shank, or leg. The hills receive from the Atlantic their vapour-laden winds after passing over Ireland. In their course from west to east, they precipitate their vapour of supersaturation in rain, or in winter in the form of snow, leaving a diminished quantity for falling upon the more easterly parts, as is found to be really the case. Compare the annual rainfall of 165 inches in the Lake district on the western coast with 20 inches at Lincoln on the east, or again : compare the annual rainfall of 86 inches at Fort William, the south-western end of the Caledonian Canal, near Ben Nevis, with 46 inches at Loch Laggan, twenty miles east, and 24 inches at Culloden at the north-eastern end of the Canal.

Most probably the rainfall was greater in earlier days before the destruction of numerous forests in this district in the time of Edward I. It is well known that vegetation conduces to climatic changes. Witness for instance the increased rainfall in Scinde, and other desert districts in India, owing to the national propensity of the Briton for tree-planting, insomuch as to have created a proverb amongst the natives of India-"Wherever the British go there rain will come.'

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The survey of this large undertaking of the Birmingham Corporation recalls to my mind, whilst considering the comparison of the rainfall on our west and east coasts, the grand and ingenious work executed in the Madras Presidency by the Engineer Officers Prendergast, Hasted, C. J. Smith, and others. On the lower western coast near Travancore the rainfall of 170 inches or thereabouts is superabundant, and originally much water ran to waste into the sea. The river Periyar has been dammed upon its western side, and its course

*Witness again the peninsula of Aden. I have statistics of the rainfall in Aden from 1834 to 1846, from which it appears that a heavy storm occurred triennially. The experiment was tried of planting trees in the gaol-yard, which were duly watered by the prisoners with undrinkable brackish water. The meteorological record of the ten years 1850-1859 gives an annual rainfall averaging 3.31 inches. Soon after the completion of the Reservoirs more trees were planted. The average annual rainfall of the eleven years 1885-1895 is 5.086 inches, as given in a letter in the British Medical Journal for October 31st, 1896, page 1318. H. C. M.

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