Изображения страниц
PDF
EPUB

ogrove ” on the hill-top at the new moon; while in the south-east of Judea at Beit-Jibreen (or Gath) we have traces of the old Philistines in the large flat-featured race, quite distinct from any others in the land. It is interesting to note that these relics of the aboriginal races are found just in the districts which we learn, from Judges i., were never thoroughly subdued by Israel.

ORDINARY MEETING, JANUARY 17, 1887. PROFESSOR G. G. STOKES, D.C.L., P.R.S., PRESIDENT,

IN THE CHAIR.

و

The Minutes of the last Meeting were read and confirmed, and the following Elections were announced :

MEMBERS :-H. C. Corke, Esq., D.D.S., Southampton; Dr. Cynie Thomas, United States.

ASSOCIATES :- The Right Rev. the Bishop of Bombay; Rev. H. M. Anketell, Chippenham; J. G. Bourinot, Esq., M.A., LL.D., Canada; C. M. Bult, Esq., C.S., J.P., Canada ; T. Barnes, Esq., D.L., J.P., Canada ; Rev. W. M. Campbell

, F.A.A., United States ; Rev. Canon C. G. Curtis, M.A., Constantinople; Professor C. C. Everett, United States ; Rev. E. A. Eardley-Wilmot, B.A.Camb., England ; Col. P. A. Elphinstone, London ; Rev. F. E. Freese, B.A.Oxon, Plymouth ; Rev. T. B. Harvey Brooks, M.A., London; Ven. Archdeacon J. Hughes Games, D.C.L., Isle of Man ; Lieut. C. W. W. Ingram, R.N., Plymouth ; J. Main, Esq., F.G.S., Glasgow ; Rev. Sir F. A. G. Gore Ouseley, Bart., M.A., Worcester ; Rev. A. Oates, Ware; Rev. T. Roberts, M.A., R.N., H.M.S. “Téméraire”; H. Stokes, Esq., Bath ; Rev. B. Waller, B.A., Southport; Rev. H. J. White, M.A., Oxon, Redhill. Hon. CORRESPONDENTS :

-T. Chaplin, Esq., M.D., Hendon ; Rev. G. A. Shaw, F.Z.S., Chingford.

Also the presentation of the following works, by their authors, to the Library :Chalk and Flint Formation. By Rev. W. B.

By Rev. W. B. Galloway, M.A.
Thirty-six Hours' Hunting among the Lepidoptera of Middlesex. S. T.
Klein, Esq., F.R.A.S.

Local Government in Canada. J. E. Bourinot, Esq.
The Philosophy of the Supernatural. By Rev. Dr. Platt.
The Progress of a Century. G. Lawrence.
The Story of the Rocks. By Professor Vail.
Science and the Revelation of Christ. By Rev. Professor Dallinger, D.D.
A Manual of Zoology (in Samoan). Rev. T. Powell, F.L.S.
The publication of the Paper read at this Meeting is delayed,

1

ORDINARY MEETING, FEBRUARY 21, 1887.

H. CADMAN JONES, Esq., IN THE CHAIR.

The Minutes of the last Meeting were read and confirmed, and the following Elections were announced :

MEMBER :-Rev. B. R. Wilson, M.A., Queensland.
ASSOCIATE :-C. M. Davis, Esq., A.M., United States.
Hon. CORRESPONDENT :-Rev. A. B. Hutchinson, A.M., Japan.

The following Paper was then read by the Author :-

ON CAVES. By T. McKENNY HUGHES, M.A., F.S.A.,

F.G.S., Woodwardian Professor of Geology, Cambridge.

[ocr errors]
[ocr errors]

OW and then it falls to our lot to find an old MS. which

throws a flood of light upon some obscure part of history. It had been put aside, buried under a heap of documents of more immediate importance, forgotten till some accident exposed it, some more careful eye caught sight of it, some more experienced judgment recognised its interest.

Such to the geologist is a cave.

He runs his eye over the contents; they may be of little value, or may settle what has long been a matter of speculation or of controversy. They may be a record of the household consumption of some wild beast in his castle; they may tell of the ancient conflict of forces of nature now at rest; or they may derive their chief interest from the character of the material on which the record is preserved.

But the MS. might be passed over, or not read aright, if the discoverer be no palæographer.

So the observer may arrive at very wrong conclusions as to the age and history of a cave, unless he be familiar with the operations of nature which form and fill such caves. This, then, is the point on which I invite discussion this evening : The formation of caves and cave-deposits, with references to some of the more interesting of those which have been explored.

To arrange our subject, I would first notice that there are artificial as well as natural caves, and many natural caves

modified by man. In quite recent times, the soft New Red Sandstone has been scooped out into cells and summerhouses. The chalk has been excavated from very early times in the search for flint, and traces of sojourn in such pits are not wanting. We need not stop seriously to discuss the suggestion that Fingal's Cave was excavated by man. The rock-hewn tombs around Jerusalem, the catacombs of Italy and Egypt are artificial caves.

All along the Vezère and other cliff-margined valleys in the South of France we see the natural caves and rock-shelters, inodified sometimes by man, walled up and occupied as storehouses, or even as dwellings. History tells us that those caves were frequently held by troops during the long occupation of that part of France by the English. The Rock of Tayac, like Gibraltar," a kind of fortress entirely hollowed out of the rock," is frequently mentioned in the history of the wars of the fourteenth and fifteenth centuries.* . And the Aquitani, when pressed by Cæsar's troops, retreated to their caves in South-central France, I have heard of a man who lived for some time in a cave in Yorkshire, coming out at night for food,-milk from the neighbours' cows, eggs, or whatever else he could lay hands on. There were many odds and ends in that cave which might have been relics of his sojourn, as well as others of more remote antiquity.†

There are hardly any records of research in caves which are known to have been occupied in recent or historic times. A systematic examination of all the caves in which history tells us the inhabitants of any district once took refuge, and an exact description of all found and observed in them, would be very interesting, and might furnish important evidence bearing upon doubtful questions.

Artificial caves, however, or artificially modified caves, form a very small proportion of those with which we have chiefly to do. The caves in which primæval man lived, and into which in old times hyenas dragged carcasses of the animals they killed or found dead along the river-courses, were all natural

. So are the celebrated stalactite caves of Germany and America. But we must inquire into the mode of formation of natural caves if we would understand the conditions which surrounded primæval man or speculate on his age.

There are sea-caves formed by the waves that lash the cliffs as if sounding them to find their weaker places. The water

caves.

* Reliquiae Aquitanice, p. 4.
+ Exploration of Care Ha, Journ. Anthropological Inst. 1874,

are

itself would soon destroy a jointed rock. As each storm-wave rolls in, it deals a tremendous blow on the fissured mass. Every thin packing of clay between contiguous blocks is soon washed out, and the fissures themselves enlarged. Then there comes into play another action. The space behind the block is filled with water; the thumping wave falls on the narrow opening on one side of it, not on the whole at once; the force is multiplied ten or a hundred times by the hydrostatic paradox, and the block is hammered out. Even in a river this operation is seen going on. Along the valley above Sedgwick's old home in Dent, thin beds of carboniferous limestone with shaley partings form the bed of the stream. The shale perishes, and the great slabs, 5 feet to 10 feet across and nearly 1 foot thick, lie side by side on the bed of the stream. Then in one of the floods so frequent in that district the fissured limestone is filled, and the surplus water rushes in a torrent over the usually almost dry channel. A slab is lifted by the hydrostatic paradox, turned over by the torrent, perhaps swept down, or often left a record of the lifting force which got it out of its bed, but in doing so destroyed the machinery by which it lifted it. So sea-Cliffs

more apt to be scooped out into caves and crannies where the rock is jointed or-crushed. Any soft, readilydecomposed dyke traversing the harder rock is also more easily removed.

But that is not the only process by which these sea-caves are formed. On the coast of Pembrokeshire, near St. Davids, there is a hole among the crags near high-water mark where, at a certain state of the tide, with each recoiling wave there is a loud sucking noise as the air is being forcibly drawn in through small, wet, weed-covered fissures to take the place of the receding water. It is known as Llesugn from the sound. Were it not for the cracks communicating with the air above we should not be reminded of this force being exercised by every wave in the cave below. Any loose material would be drawn back with the wave, and perhaps carried out of the cave altogether. Many of us are familiar with the phenomena known as “Blow Holes,” or “Puffing Holes.” The incoming wave fills the tapering cave, and, just as the bore coming up a tidal river rises higher and runs more fiercely when the converging banks force it to pursue its way through a more contracted channel, so when the wave rushes into a narrowing, funnel-shaped cave, with a small aperture communicating with the surface, the water is forced up through the opening, and often a spout of spray is carried high into the air. All these phenomena tell us of the enormous force exerted by the waves

1

[ocr errors]

upon the coast, and explain how caves must everywhere be formed where shattered or softer rock is exposed to the lash of the wind-driven sea.

But this is not all. The wave picks up great boulders and hurlsthem at the rocks that bar its advance. It is quite common, after a storm, to find large stones lodged on a promenade or pier, where they must have been caught up in the wave and thrown upon the land. Stones are always carried forward up an incline as far as the waves advance; but the cases I refer to now are those in which the stone has been thrown up to the top of a vertical wall. The last place I remember having seen this was in a great storm a few years ago at Hunstanton. The same thing takes place on a grand scale on some of the wild, rocky cliffs of North-Western Scotland, for instance. The Director-General of the Survey has described how in storm, great blocks are hurled up on to the top of the cliff near the Old Man of Hoy.

The force of the Atlantic waves at the Skerryvore Rocks, as estimated by the marine dynamometer, an instrument designed by Thos. Stevenson for this purpose, was found to be as much as 6,083 lb. to the square foot.*

From the height to which the spray was thrown, he inferred a pressure of about 3 tons to the square foot; and further recorded that a block of stone, estimated at 48 tons in weight,

was seen to move under the influence of each wave.”+

On the Bound Skerry of Whalsey, which is only exposed to the waves of the North Sea or German Ocean, he had found · masses of rock weighing 9} tons and under, heaped together by the action of the waves at the level of no less than 62 feet above the sea ; and others ranging from 6 to 131 tons were found to have been quarried out of their positions in situ, at levels of fron 70 to 74 feet above the sea. Another block of 77 tons, at the level of 20 feet above the sea, had been quarried out and transported to a distance of 73 feet

over opposing abrupt faces as much as 7 feet in height."

It is clear that such waves and such boulders would make short work of broken rock or a rotten dyke, and any old cave or fissure opened out by the sea would not be likely to have much of the original deposits left in it. The first storm would clear out all earth and bones, and leave in its place only the well-worn pebbles of a rocky shore,—the battered shot of nature's great marine artillery: A sudden upheaval would leave the cave either quite clear, if it was on a clean,

[ocr errors]

* Stevenson, Thos. Edin. New Phil. Jour. xlviii. 1850, p. 41. + Ditto, Proc. R. Soc. Edin. vol. ii. 1844-50, p. 13. I Ditto, Proc. R. Soc. Edin. vol. iv. 1862, p. 200.

« ПредыдущаяПродолжить »