POSTSCRIPT.

By JAMES G. WOOD, M.A., F.G.S., F.R.Met. Soc.

HAVING through the courtesy of Mr. Moore being favoured with an early perusal of his paper, I have further to acknowledge my indebtedness to him for being allowed to supplement it with a few observations.

To get rid at once of the personal element, and to justify my having appeared to speak as if with some authority, I may say that my acquaintance with the Wye began in 1852; that from 1854 to 1864 the windows of my old home overlooked Chepstow Bridge; and during those and many subsequent years my aquatic pursuits led me to observe the tides with much precision; and later on until recent years I was a constant visitor to the place, and kept closely in touch with everything of interest that occurred there.

1. THE HEIGHT OF WYE TIDES.

In my letter to the Standard I avoided, as much as possible, reference to local details which would be unintelligible, or uninteresting, to the general reader. Lest, however, this question should hereafter be mooted again, it will be desirable to place on permanent record the data on which I based my conclusions.

I fixed my datum-line at a point 9 feet below the top edge of the pile sheeting of the "starling" of the pier on the Monmouthshire (or South) side of the centre arch of the Road Bridge, under the centre line of the Bridge. I once (and only once) saw the water down to the level of that point, leaving only 3 feet of water in the deepest part of the channel under the Bridge, where it is naturally washed out by the scour deeper than elsewhere. This was so exceptional an occurrence that I am not surprised that Mr. F. W. Dibbin (the engineer referred to in my letter), fixed his average low water 1-29 feet above my datum; and Mr. Hughes (mentioned in Mr. Barry's letter), fixed it 3 feet above my datum.

Starting from this datum-line the following are the measurements of the important points, taken partly from Mr. Dibbin's record; partly from Mr. Hughes' scaled drawings; and partly from the Ordnance Survey. I have tested them in every possible way; and can find no discrepancy between the various measurements.

Datum-line (3 feet above deepest point of river bed, and 9 feet

Feet above datum-line.

Edge of starling under centre line of bridge, south side of centre

Top of piers of bridge (23:45 feet above Ordnance datuin)

42.00

Doorstep of shop at corner of Bridge Street and St. Ann's Lane

48.13

Tide of January, 1846 ...

Tide of October, 1883-also the level of under-side of spans of land

arches (30 feet above Ordnance datum)

Tide of 1799

Crown of intermediate arches (under-side of spans)

Crown of centre arch (do. do.)

...

Feet above datum-line.

48:39

48.55

49.13

53:00

56.00

It thus remains that the highest tide of which we have any authentic record was 49'13 feet above the lowest point of ebb that I ever saw; 47'84 feet above Mr. Dibbin's low water line; and 46:13 feet above Mr. Hughes' low water line. If any one should hereafter see the water lower than my datum, or more than 7 feet 14 inches above the piers, he will "please note."

At the same time it must be remembered that the true measure of the range of a tide is the difference between the levels of high and low water of that particular tide, so that probably no tide has achieved a range equal to the above figures. This is the more probable because exceptional tides seem to have been concurrent with land floods. In January, 1768, when the big tide referred to below occurred, there were great floods at Hereford, Ross, and Wilton. In January, 1846, there were great floods in the upper Wye and the Lugg, "none such since 1795, when Hay Bridge was washed away "; and the tide of 17th October, 1883, occurred after a very wet September, and a few days after some exceptional rains in the Wye Valley. The ebb on such occasions would not go down to within 7 feet of my datum.

It would be interesting if the original error could be run to earth. It probably began with the tide of 1768, to which Lyell referred, as quoted by Mr. Moore. Cliffe's South Wales (1848) says:-"The tide (at Chepstow) rose in January, 1768, to an altitude of 70 feet to the injury of the old wooden bridge.” Lyell, in Principles of Geology, Vol. 2, p. 26 (1840) says:-“At Chepstow [the tides] reach 50 and sometimes 69 and even 72 feet," and gives as his authority Captain Beaufort, R.N.; and Norie's Epitome of Navigation (1835) gives 70 feet as the average height.

These “authorities" must have proceeded upon one con common source, without an attempt at verification. A tide of 70 feet would have covered the old bridge by about 20 feet, as will be readily seen from old engravings of it; and would have wrecked all the shipbuilding yards and warehouses which made the town then a place of importance, and swamped half of the then town also; but there is no record of such a catastrophe. The damage to the bridge was probably caused more by the flood above mentioned than by the tide.

It occurs to me that probably on that occasion a survey was made; and the surveyor measured the tide as 72 links, equal to just 47 feet 6 inches, or very nearly what we now know to be the maximum range. This measurement may have been afterwards spoken of as 72 feet; and hence the mischief began; and went on till the railway engineers took the matter in hand.

To prevent any misapprehension hereafter, I would point out that Mr. Barry's inference, that the tide of 1883 covered the iron palisading of the bridge, was based on the assumption of the accuracy of the figures which have now been

disproved. The tide, as a fact, was much below the top of the palisading at its lowest point.

I said in my letter that "tidal waves were due to causes other than those which produce tides. I had in my mind the tidal waves in the Dart to which Mr. Moore has referred. Some notes on these from information obtained by ine at Totnes at the time will be found in the Meteorological Magazine, Vol. 27, p. 115. 2.-VARIATIONS OF ABSOLUTE LEVEL OF HIGH WATER AT DIFFERENT POINTS.

It will be well worth while to institute a series of observations, at points along the estuary of Severn and its tributaries, of the relative heights of maximum tides referred to Ordnance datum. At present I can only offer the following:

Mr. Worsley-Benison has set out a copy of the brass in Goldcliff Church. The flood there mentioned was no doubt due to tide and not to land water; for the tide on the evening of 20th January, 1606 (O.S.) will be found (making due allowance for change of style, &c.), to have been the fifth after the full moon; which would make it "the top of the springs."

The brass is 24 feet above Ordnance datum; or 9 inches only above the Piers of Chepstow Bridge. Assuming, therefore, that the tide of 1606 was no less than the tide of 1799 (and it was possibly greater), we have a difference of at least 6 feet 4 inches in a shore distance of about 16 miles.

I have it also on the authority of Mr. Dibbin, that all exceptional tides were marked on a brass plate in the kitchen of the Dog Inn, at Over, near Gloucester. If that is still extant, and its relation to Ordnance datum be ascertained, very useful information may be gained.

Such comparisons may teach us a good deal as to the effect on tides of the contours of shore lines; and may lead also to other considerations. Geologists have noticed on the shores of estuaries, and notably in the Gulf of St. Lawrence, ancient "raised beaches," the level of which gradually inclines upward toward the sea; and have explained the fact on the hypothesis that the elevation, which left the beach high and dry, has been more marked at the mouth than at the head of the estuary. It may be that the true explanation is to be found in some such variation of tide level (under the then conditions of the estuary) as I have shewn to exist now between Goldcliff and Chepstow.

From a report of Mr. Bunt, the observer of the Tide Gauge at Bristol, quoted in Cliffe's South Wales, it appears that the level of high water at the Hotwells is one foot above that at King Road. He also notes that the tide of 29th January, 1846, was the highest registered by him; its height being 38 feet 8 inches above the sill of Cumberland Basin.

3. THE BORE IN SEVERN.

I have nothing to add to Mr. Moore's description, or Mr. Miller's explanation, of the phenomenon.

Locally it was called the "higre," or "hygre"; and this has been fancifully derived from "eau-guerre." It is really a corruption of " eagre" the English equivalent of the Scandinavian "Bore." It is derived from the A.S. égor=sea,

or water. Professor Skeat quotes from Dryden, "But like an eagre rode in triumph o'er the tide."

Just below Sharpness lies the "Sanager" sand. This is probably a corruption of san (imp. of sinnau A.S.)=be mindful of, and égor=the flood. The spot would naturally be that where the cry "Flood, oh"! or its Saxon equivalent, arose on such an occasion.

4. THE BORE IN THE WYE.

I am glad to be able to add a note on this; as it seems to be generally unknown. I have found even fishermen and boatmen entirely ignorant of it.

It commences a little more than half-a-mile above the Chepstow Road Bridge, at a point a few yards above the old Roman crossing beneath the Alcove in the Piercefield Woods. Its course extends upwards for just a mile, through the straight reach called "Longhope" reach, or "The Hope."

About 250 yards above Chepstow Bridge the river takes a very sharp bend (the second half of an "S" curve) northward under the Castle. At low water, the channel is immediately under the Castle rock, on the Monmouthshire (or concave) side. On the Gloucestershire (or convex) side the bank, of alluvial clay, slopes somewhat steeply; but at low water there stretches out from it an extensive "spit" of firmer ground, forming a flattened beach, which very much narrows in the channel, and in no part rises to any considerable height above low water mark.

Except a few stones opposite the Bridge Quarry, and the starlings of the bridge, this spit is the first serious obstacle which the flood tide meets after it enters the Wye.

The similarity of this spit to the "Noose" in Severn mentioned in Mr. Moore's paper is very remarkable; only it is on a smaller scale, and the direction of the bend is reversed.

Above the spit, to the place where the Bore forms, the banks are somewhat steep; that on the Monmouthshire side being rocky. Soon after passing the Roman crossing the river bed presents a narrower section at low water level, with the banks at lower angles.

The phenomenon may be best observed from the summit of the Penmoyle cliffs which command the whole of the "Hope." The time to observe is at the making of the flood on the fifth tide after new or full moon; and preferably at the St. David's tide in the beginning of March; or at the latter end of September.

If, however, much fresh water is coming down, so that the "spit" is not laid bare, there will be no bore.

The explanation is similar to that given of the Severn Bore. The flood tide, rushing up through the bridge, is backed and ponded up by the spit; just as the Severn tide is by the Noose. At length the spit is covered; possibly some of its top layer also gives way; the body of water rushes on, and, at the narrowing in again of the channel, mounts up and spreads out at the same time over the flattened banks. It advances up the Hope with a head of about 2 feet, and a roar plainly heard on the cliffs above. As it passes, the ebb, which immediately

before was making down, is turned back, and the flood is seen to be strongly making up.

I never saw it pass round the bend at the north end of the Hope; but it dies out opposite the upper Llancaut Quarry where a weir' shows at low water.

5. THE INTERMITTING WELLS AT CHEPSTOW. Within a few yards to the north of the well mentioned in Mr. Moore's paper is another well sunk in the cellar of Gwy House, in Bridge Street. Of the action of the former well I know nothing. The latter I know very well, having been a frequent visitor at the house.

I could never satisfy myself that the water actually receded from this well on the rising of the tide. But this is certain that at high water the well could readily be pumped dry; and no more water would come in until the tide went down. It is possible that on such occasions the Gwy House pump may have drained the neighbouring well; and so have given rise to the belief that the water receded.

I have on several occasions, (perhaps four or five), known the water to rise up in the well and flood the cellar to a depth of about 18 inches; which (speaking from memory here) would be about 1 foot below the 1883 level. This would happen after very heavy rainfall, accompanied by an exceptional tide.

The well is 400 feet from the river bank; but on no occasion, and under no circumstances, is the water brackish. It is strongly impregnated with lime salts.

On reference to Sheet 35 of the Geological Survey a fault (which for distinction I call the main fault), will be seen starting a little south east of the bridge and going north for one and three quarter miles cutting the river bed at four points.

The wells in question are sunk either on or very slightly to the westward of this main fault.

I doubt if the whole length of the fault is shown on the Survey. I think it probably extends to, and is cut off by, a cross fault visible (but overlaid by "dolomitic conglomerate") in the quarry at the Railway Station; and is also cut off, at the north end, by another cross fault (not shown on the Survey) starting 100 yards south west of the Cockshut, crossing the river, and passing a little south of the Liveoaks Farm.

On the west of the main fault the dip is eastward; or against the fault. About half-a-mile north of the bridge, in Chapel House Grove, is a considerable area of Farewell rock (not shown on the Survey), pitching east 33° against the fault. This indicates by comparison with Tidenham Chase a downthrow west of 460 feet.

The conditions are therefore favourable for the inclusion between these faults of a large body of water, entering at the outcrops of carboniferous limestone to the west of the Wye Valley, and of the area of Farewell rock just mentioned.

The explanation I have to offer is, that the wells are fed by the fault; and that the water, under certain conditions (that is when unaffected by heavy rainfall) comes under the river along the fault; and that, under the pressure of a tide with a vertical head of 40 feet, the passage along the fault (which has a considerable dip)