be much finer.

It probably took a very long time for the central part of this Diorite to become solid, hence we should expect to find its texture there to be more coarsely crystalline, while what is in contact with the original rock would have a homogeneous and even a glassy appearance. The same remark applies to other igneous rocks as well, and has led to their classification. Some at great depths in the bowels of the earth have taken enormous periods of time to cool and become solid. In these are found crystals, sometimes of very considerable size. They are termed granites, syenites, gabbros, classed according to the percentage of silica that they contain; others, poured out over the surface, have assumed an altogether different aspect from the fact that they have cooled more rapidly; they are termed rhyolites, andesites, basalts. Now it must be remembered, that, though so unlike in appearance, the ultimate materials of which these rocks are formed respectively may be identical; and thus an important clue is afforded to determine their history and the conditions which attended their deposition.

It is well to bear clearly in mind the sequence of events which preceded the occurrence of this igneous outburst. The series of Palaeozoic strata, up at least to the Old Red, had already been deposited: each of its members had been consolidated into hard rock, when, owing to some disturbance of the earth's crust consequent on its contraction and the folding of its surface, a portion of the great molten mass which forms the centre of the globe was forced up into the fissure that was created. It is a striking fact that we are literally walking each day of our lives on what might, at any moment, be a volcano. If we were to make a bole in the earth beneath our feet, we should find that at the depth of ten miles the heat would be sufficient to melt iron, and at twenty miles, all known substances. Not that they are actually in a liquid condition, since the enormous superincumbent pressure is sufficient to prevent this. But the fact that, according to Professor Prestwich, an increase in temperature of one degree Fahrenheit is found to occur for every 45 to 50 feet sunk in deep mines, proves that a heat such as I have stated would be the result. This great central heated mass, then, being only kept in a solid and quiescent state by the enormous pressure of the crust above it, it may easily be supposed that a certain diminution of that pressure is only required to set free some of the force stored up. A slight movement in the surface rocks caused by the contraction that is always going on, and the infiltration of water through the cracks caused thereby, would supply all the conditions necessary for an outburst of lava; either violently, through the crater if a volcano, or, more quietly, by welling up through fissures, as it has done in this instance.

There is good reason to believe that there were certain epochs of exceptional igneous activity such as I have spoken of in past time. What are now called Archæan rocks are believed by some competent authorities to represent matter in a plastic condition previous to the deposition of any sedimentary rocks. Of this state of things we have but very imperfect knowledge; but since the formation of sedimentary strata there is positive evidence to show that during the Ordovician, or, as Sir R. Murchison called it, the Lower Silurian Epoch, again in the Carboniferous, again in the Permian, and lastly in the Tertiary, there have been powerful volcanic disturbances, with intervals of repose between them. It must have

been, of course, to one of the last two of these that this mass of Diorite is due, probably to that in which the basalt of the Clee Hills in Shropshire was poured forth, and which took place after the coal measures had been formed.

I shall not attempt to enter upon the complicated subject of the composition of igneous rocks further than to say that Diorite belongs to what is called the sub-acid group; that is, to rocks that contain less silica than the granites and rhyolites. The determination of this fact depends on chemical analysis, but may also be made by the examination of thin sections under the microscope in polarized light, such as you have this day had an opportunity of seeing."

A small instrument, ingeniously devised for field use by Mr. La Touche, composed of a pair of Nichol prisms, had been previously handed round to illustrate the remarkable change of colour and the development of texture seen in various minerals when viewed in polarized light, nor can it be too widely known amongst the members of the Club, that Mr. La Touche has a friend, Mr. Parry, of Lydbury North, Salop, who is capable of making the delicate sections of mineral as required for this instrument.

Thanks having been accorded to Mr. La Touche for this unexpected impromptu explanation, time was called for resuming seats in the carriages, which were pulled up again at Lugwardine Court, for tea and other refreshments, by the invitation of Sir Herbert Croft, Vice-President, after which the members, grateful for their repast crowning the pleasures of the healthy outing, returned to resume their duties at their respective homes.

Woolhope Naturalists' Field Club.

JUNE 30TH, 1891.

THE second Field Meeting of the Club this year took place on Tuesday, June 30th, at Aberedw, in Radnorshire. The meeting was well attended; twenty-nine members took their seats at the Barton Station, Midland Railway, Hereford. The party, gathering contingents at the intermediate Railway Stations, mustered forty-eight upon arrival at the rendezvous, Aberedw, and was thus constituted: The President, Rev. Sir George H. Cornewall; Vice-Presidents, Sir Herbert Croft, and Rev. Augustin Ley; Rev. J. D. La Touche, President of the Caradoc Club; Members, Revs. G. E. Ashley, H. A. Barker, W. D. V. Duncombe, W. Elliot, C. S. Hagreen, E. J. Holloway, Plaskitt C. Lewis, H. B. D. Marshall, T. P. Powell, M. G. Watkins, and H. T. Williamson. Captain C. O. Dansey Oldham, Captain E. A. Swainson, Messrs. C. G. Blathwayt, Cecil Butler, J. Carless, jun., R. Clarke, P. C. Cleasby, G. Cresswell, James Davies, E. H. Greenly, T. C. Paris, G. H. Phillott, W. Pilley, E. L. G. Robinson, H. C. Moore (Honorary Secretary), and James B. Pilley (Assistant Secretary); with the following visitors: Sir Richard Harington, Revs. A. G. Adamson (Rector of Aberedw), W. E. T. Morgan, Walwyn Trumper, T. Williams (Llowes), W. Gordon Williams (Gwenddwr, Breconshire), Surgeon-General Perry, Messrs. William Boycott, J. Cockcroft, W. Cornewall, L. W. Humphrys, Thomas La Touche (of the Indian Geological Survey), Norman La Touche (of the Public Works Department, India), H. T. Timmins (of Edgbaston), and a few others whose names were not obtained.

Upon arrival at the Three Cocks Junction, the interval of one hour was profitably occupied in transacting some business of the Club, Mr. Charles P. Bird, of Drybridge, Hereford, was re-elected a member upon his return from India, and the names of the following gentlemen were proposed to be balloted for at the next meeting-Mr. Digby S. W. Nicholl, F.L.S., F.Z.S., M.B.O.U., &c., of the Ham, Cowbridge, author of The Birds of Glamorganshire, and Mr. Warre Prescott, of King's Pyon House.

Seats in the special carriages having been taken, the members proceeded on their journey from the Three Cocks Junction by the Cambrian Railway. After a few minutes run a hasty glance of a horse-shoe bend of the river Wye was obtained upon both sides of the iron lattice bridge which carries the railway over the river. Upon the left side a series of natural terraces present the appearance of an artificial breakwater. Upon the right is the beautifully situated rectory of Boughrood, with the modern house, Boughrood Castle, above. The ancient building is said to have been held in 1140 by Eineon Clydd-(Medieval Military Architecture, page 107).

After leaving Boughrood Station the line of railway runs by the river bank, and continues on a course of 27 miles nearly parallel with the Upper Wye past Builth to Rhayader, through a valley of charming scenery, the river forming here the boundary between the counties, Radnorshire on the right, and Breconshire on the left or western, side of the railway line journeying towards Builth. About half way between Boughrood and the next station, Erwood, the tributary of the Bachhowey is crossed, where on July 18th, 1867, a red-letter day in the annals of the Woolhope Club, the railway authorities stopped the train, and erected a platform for the members to alight and spend the day at the beautiful waterfalls of Craig-y-pwll-ddu, where are observed remarkable contortions of Ludlow rocks. (See Transactions, 1867, page 40, et seq.) Upon this historic ground we must dwell for a few moments to remind ourselves that Sir Roderick Murchison has pointed out that the stream here separates the Upper and Lower Ludlow rocks. Upon the south, Trewern Hill, a continuation of the Begwn range, is of the Ludlow formation, whilst still more southerly the Old Red Sandstone rocks appear. In the Ordnance Geological Survey the line of demarcation between the Old Red Sandstone and the Ludlow is a well defined line, about a mile north of Erwood. The bold hill of Garth, 1,065 feet high, is just on the Old Red Sandstone, Llandeilo-graban and Llande wi-fach are both of the Lower Ludlow formation. At Boughrood is a narrow outlier of Lower Ludlow along the river Wye, about a mile in length, another of similar size on the right side or east of the Wye, a mile further north, against the stream of the river upwards,* whilst a much larger outlier of the same Lower Ludlow crosses the Wye just before reaching Erwood. These Ludlow rocks extend from Erwood to Corn-y-fan, about six miles north-west of Brecon. In Records of the Rocks the Rev. W. Symonds recommends the geologist after examining the Upper Silurian section on the banks of the Wye near Trewern, to follow up the rocks in ascending order by Cusop to the Brownstones on the summit of the Black Mountains, and on page 239 he exhibits an instructive section of this walk. From this range of hills demonstrating the passage downwards from Old Red Sandstone to the older rocks beneath them Sir Roderick Murchison obtained the key to the whole Silurian system. Our geologists would have preferred to tarry awhile, but the train hurried them along their course almost parallel with the rocky-bedded Wye until other historic ground was reached at the station of Erwood. At this place the river was forded by the English troops in the pursuit of Prince Llewellyn. The name of the ford is Cafan Twm Bach, or little Tom's boat, where now a very comfortable-looking hostelry occupies the Radnorshire bank within three minutes' walk of the railway station at Erwood. A repetition of the oft-told history of Llewellyn's betrayal by the blacksmith who reversed his horses' shoes is unnecessary-suffice it to say, in the words of the learned Selden, that on December 22nd, 1282, in the 48th year of his age, perished "as great and

*The right side here mentioned is properly the true left bank of the river, it being necessary always to bear in mind that the banks of a river are always designated right and left banks as you travel with the stream down the river from its source to its mouth, not against the stream from its mouth to its source. In this paragraph of the text, the terms right and left have been used according as objects were situated right or left of the traveller from Three Cocks towards Builth.

worthy a prince as ever the third part of this island was ruled by," and that one of the most carefully-recorded accounts of the circumstances is to be found in Transactions of the Woolhope Club for 1866, page 230. Leaving Erwood station, the Old Red Sandstone is shortly lost sight of; the hill upon the right hand of the railway exhibits the appearance of ruins of an ancient fortification with a series of rocky walls of circumvallation rising above each other successively. These rocks of Upper Ludlow tilestones, with a horizontal stratification, have in some instances assumed grotesque shapes owing to disintegration and weathering of the soft parts. Near Aberedw, just above Mr. T. B. Mynors's residence "Pont Shony," (Johnny's bridge), of which Mr. T. M. Baskerville of Clyro Court is the proprietor, are representations which carry the mind to the monster Sphinx and other gigantic relics of Egyptian antiquity.

At Aberedw railway station the members were met by the Rector of the parish, Rev. A. G. Adamson. The first object of search was for a rounded boulder, a granite-like rock which Mr. Moore had observed on his visit here about a month ago and which appeared to have fallen from the drift exposed here. Mr. Moore had chipped off a fragment and sent it to the Rev. J. D. La Touche for examination, who reported of it as follows: "The chip of the boulder turned out to be very interesting. I have made a good section of it which has revealed some fine structures. It appears to be a volcanic tuff, with large crystals of plagioclase felspar, and cavities filled with zeolites which make a splendid display of colour in polarized light." The search for the boulder, however, proved fruitless; it had been removed and probably broken up for road-mending. Portions of igneous rocks were discovered in the drift.

Mr. Adamson conducted the members to the contiguous ruins of one of Prince Llewellyn's castles, which in Vol. 1, page 109, of Clark's Medieval Military Architecture is said to have been built by Ralph de Baskerville, one of the Norman invaders. Alas! that the march of civilisation should find it incumbent to deliberately demolish so interesting a relic of history. Upon forming the railway line, the contractors, not successful in their first attempts to remove from off the face of the earth the two circular towers on the south side of this stronghold, accomplished this ruthless vandalism by increasing the number and quantity of their charges from one barrel of gunpowder to three barrels. The parish clerk, David Williams, now aged 79, was a witness of their proceedings. He recalls to mind that the wall interiorly had many curious recesses like large cupboards. Surely in the present days of reformed churchwardens and scarcity of Goths, the embankment would have been faced with a wall of masonry where stone was abundant, and the whole would have been preserved, or the line would have been diverted a few yards, and thus the feelings of posterity would have been spared so deep a wound. The fragments that remain of this stronghold show that it was a square work of about forty yards each side, with a round tower at each angle, and surrounded by a deep dry ditch, enclosing an area of about one-third of an acre. Three hundred yards southeasterly upon the north bank of the river Edw is a conical mound, the upper surface of which has been artificially elevated perhaps fifteen feet by the excavations from its surrounding ditch. Exposures upon its declivity show that its base of the