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Essay on the Formation of Caves
Essay Contents:
- Essay on the Formation of Caves
- Essay on Stalactites and Stalagmites
- Essay on the Tenby Cave
- Essay on the Tenby Fissure
- Essay on a Cave in North Wales
- Essay on the Victoria Cave
- Essay on the Buxton Cave
1. Essay on the Formation of Caves:
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Any one who has been to various parts of our British coasts will have seen that in some parts caves are forming or have been formed, while in others there are no vestiges of them. For a cave to be formed on the coast the rock must be hard, and so in the soft beds which make much of our eastern and southern coast-line we find no sea caves.
Along many of our other coasts, however, caves are numerous, and the condition for their formation is that there should be a line of weakness of some kind upon which the sea can work. In some cases a soft bed occurs between harder ones, and then the sea may scour out the soft one.
If the beds are more or less horizontal this may not produce a cave, for the upper bed may be unable to keep up and form the roof of the cave, but falls down; but if the beds are tipped up, then the upper hard bed often remains as a covering to the hollow formed by the removal of the lower and softer one. At other times a joint plane allows the water to get to work and gradually remove the rock below, and so well-jointed rocks frequently give rise to caves.
It may happen that these caves get cut through a cliff and open into the land behind. Extra high tides or gales assist in this cutting process, and much may be done by the waves forcing air into the cave. When this imprisoned air presses its way out again if often makes a booming noise, and so the cavity is called a blow-hole.
Land caves, however, are known as well as sea caves. These may, of course, be merely sea caves raised by the uplift of the level of the earth above the sea, and such caves are well seen along the west coast of Scotland; but in other cases their cause is very different—they are made not by being bored but by the rock being dissolved. They are found in those parts of the country which are made of hard limestone, and so we find them for the most part in those districts which are made of Carboniferous limestone.
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The rock being a limestone is made almost entirely of calcium carbonate (CaCO3); this material is insoluble in pure water, but soluble, to a certain extent, in water containing carbonic acid (H2CO3). Now rain-water coming down on the soil carries down to the rock beneath the surface some acids derived from the plants which grow in the soil, and this acid attacking the calcium carbonate forms carbonic acid, which is carried off by the water and dissolves calcium carbonate, when it meets it, in the form of calcium bicarbonate (CaCO3 H2CO3). Thus large quantities of limestone may be gradually dissolved away, and so a cavern may be formed.
Whenever the water containing the solution of bicarbonate evaporates to a sufficient extent the carbonic acid goes away and the calcium carbonate is deposited as a white or yellow mass. This is frequently seen in streams in limestone districts, and in the joints in limestone in quarries, but is usually especially well seen in caverns.
2. Essay on Stalactites and Stalagmites:
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When the water drops down from the roof of a cave evaporation often occurs, and so little beads of calcium carbonate are first formed there, and in the course, of years these continue to grow until long pendent masses are produced called Stalactites. A similar deposit may be formed on the floor of a cave, and it is then called Stalagmite.
But it is not only in natural caves that stalactites are formed. A railway bridge may be looked on as forming the roof of an artificial cave, and lime is used to make the mortar which helps to make the bridge. This lime, owing to the action of the air, is converted into limestone, and this is in time dissolved in just the same way as natural limestone, and is re-deposited where the water evaporates. In consequence of this one may often see stalactites several inches long hanging down underneath a bridge.
Caves have, of course, been used both by den-loving animals and by man as habitations, and the remains of these inhabitants have often been buried during the lapse of many years by the stalagmitic deposit formed over them.
Consequently the floors of caves have proved fruitful places for excavations, and we have gained great knowledge of the past from discoveries in them.
In order to follow the evidence yielded by our British caves it will be well to describe what has been found in a few which have been investigated with care.
3. Essay on the Tenby Cave:
A cave and a fissure near Tenby were investigated in 1881, and a considerable number of bones were discovered. The Coygan Cave, about 250 feet above sea-level, is in mountain limestone which forms a part of an ancient line of sea-cliffs.
The cave floor was covered with a deposit of stalagmite, sometimes 12 inches thick, which was often concealed by recent falls of blocks from the roof. There were very few bones of recent animals above the stalagmite, and after breaking through this the explorers came upon cave-earth and dug a trench through it.
They found a number of teeth and jaws of the cave- hyaena and very many splinters of bones, all bearing the tooth-marks of the hyaena. Horses’ teeth were very common, and a few gnawed bones of the same animal. Many teeth and a few bones of the mammoth (a species of elephant) were seen and numerous bones and teeth of the woolly rhinoceros. Besides, the bones of these animals there were also found those of the elk, red deer, reindeer, roe deer, cave-bear, cave-lion, ox, wolf, and fox.
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From beneath 10 inches of stalagmite, embedded with the bones of the mammoth and rhinoceros, were two flakes of flint evidently fashioned by man. Several bones were found which appeared to have been cut by man, one apparently having been meant to be an awl. There seems no doubt whatever that the cave was a hyaena den, that the hyaenas dragged into it the remains of animals for food, and that the gnawed bones were left and now remain entombed. At one time, however, cave-men frequented the cavern and left behind their implements.
Round parts of the South Welsh coast a submerged forest occurs amongst which mammoth remains have been discovered, and we can picture to ourselves the Bristol Channel of today as being then a plain covered with vegetation amongst which were streams inhabited by the hippopotamus, while the elephant roamed at large. The weaker members of these plain-loving animals would fall a prey to the hyaenas, and parts of their carcasses, dragged up to the security of the cave, would have been devoured at leisure.
4. Essay on the Tenby Fissure:
The other opening near Tenby which has been investigated is Hoyle’s Mouth, and is a narrow fissure rather than a cave, as it is about 200 feet long and about 5 feet broad.
The innermost chamber had been dug up in previous years, but in 1881 its earth yielded bones of brown bear, reindeer, ox, red deer, wolf, fox, horse, and flint chips. Investigation was then carried out of the contents of a portion of the cave about 140 yards from its mouth. Here, under 4 inches of stalagmite, teeth and bones of the brown bear and a single flint flake were found.
Then the entrance of the fissure was examined. Here bones of reindeer, hog, and ox were found, with bones of recent animals, human bones, and flint flakes.
About 10 yards from the entrance are the remains of a hearth made of charcoal and burnt bones covered by about 9 inches of stalagmite.
This fissure differs very markedly from the Coygan Cave in the kind of animal which is found in it. In the one case we have a hyaena den and in the other case a cave used as a habitation by men, who made a hearth there, split and broke many of the animals’ bones, which are now found in the cave, and left lying about the shells of marine shell-fish, which they used for their food.
5. Essay on a Cave in North Wales:
In 1884 some caves in the valley of the Clwyd in North Wales were examined by Dr. Hicks. They were in Carboniferous limestone about 40 and 60 feet above the stream in the ravine below them. A deposit of glacial clay covers the bottom of the ravine and the slope opposite the caves, while 400 feet away from the caves on their side of the ravine is a deposit of sand and gravel containing scratched boulders and shell fragments.
The ravine was therefore formed in pre-Glacial times and filled up by glacial deposits which have been later on gradually washed away, and this denuding process still continues, patches of the glacial material being left on the sides of the valley and a continuous bed of it along its floor.
On working into the cave called Ffynnon Benno, there was found on the top a foot of surface soil and then 6 inches of blocks cemented together by stalagmite. Under this was 2 feet of cave-earth with bones and flint implements, and finally 2 feet of gravel made up of local materials with angular blocks of limestone below.
The top surface-soil contained a few bones of sheep and of the domestic fowl, and is probably a very recent accumulation, but below the stalagmitic layer were found bones in considerable quantity, while the lowest layer must have formed the floor of the den at the time it was inhabited.
A portion of the jaw of a rhinoceros was found at one spot in the cave-earth, large fragments of the limb bones of mammoth, and a flint implement.
The cave has two openings, and the above finds were made in the larger one. The other must have been a hyaena den, as remains of this animal were plentiful and mixed with them many gnawed bones; but other ones must have been broken by man and some of them were worked, one having a hole bored in it. Flint implements also prove that man inhabited this cave at the same time as the mammoth and woolly rhinoceros roamed the plain without.
The other great cave is the Cae Gwyn Cave; it is a long, thin opening with a side tunnel running into it. Its floor was formed of 2 feet of clayey sand containing a few bones of recent animals, then 8 inches of clay with stalagmitic layers, then 2 feet of sandy clay with pebbles, and in this layer bones of extinct animals and a flint, this last resting on a mass of gravel. These layers were found throughout the cave, though they varied in thickness.
In the bone-earth were found over eighty jaws of various animals and more than 1300 teeth, including 400 rhinoceros, 15 mammoth, 180 hyaena, and 500 horse teeth.
Besides the remains of these animals the cave-earth in the two caverns yielded those of the lion, wild cat, wolf, fox, bear, badger, wild boar, great Irish deer, red deer, roebuck, and reindeer.
We have here as in the Tenby caves evidence that these caves were hyaena dens, and were at one time inhabited by early man.
The remains of the hyaena’s prey enable us to picture in some way the ancient plain of the vale of Clwyd as a huge feeding-ground of the rhinoceros, horse, reindeer, and other animals.
6. Essay on the Victoria Cave:
The Victoria Cave, near Settle, was so called because it was discovered on the day of the late Queen’s coronation, and the discoverer collected from it many ornaments and implements of bronze, iron, and bone, pottery, animal remains, and coins of Trajan, Constantius, and Constantine.
The bones belonged to the red deer, roebuck, pig, horse, cow, goat, badger, fox, and dog. In fact, the remains were just those that are so often found near Roman villas or towns and were without doubt left there either towards the end or soon after the Roman occupation of Britain.
In 1869 permission was obtained to systematically examine the contents of the cave. At the outside a sloping mass of fallen scree, broken away from the cliff by frost, almost blocked the entrance, and below this came another mass of glacial drift, but inside the explorers came upon the true cave deposits.
These consisted of an upper and a lower cave-earth separated by a layer of laminated clay. The fallen scree had formed a small plateau on which the cave-dwellers had lit their fires and cooked their food. The top 2 feet of this plateau were made of angular fragments broken away from the cliff above, and below there was a dark layer made of fragments of bone more or less burnt, burnt stones which had made the fireplaces, pieces of pottery, and coins of Trajan and Tetricus.
As the explorers worked inwards the upper layer or fragments died away and a black layer was found uncovered by any other deposit. It was from this layer that the original discoverer had obtained his collection of remains. During the final investigation of the cave plenty of other ornaments and implements were found and very many bones.
The Celtic short-horn formed the common food, goat and pig and horse were also eaten, and occasionally deer supplied the cave-dwellers with venison. Two species of domestic fowl and very many duck and geese were also used as food.
Some barbarous imitations of Roman coins assigned to the period of the Roman evacuation suggest that the cave was inhabited at that period, and this would explain the abundance of articles of luxury in such a retreat. We may place this period of this inhabiting of the cave at some date not earlier than the fifth century.
Beneath the Romano-Celtic layer was a thickness of about 5 or 6 feet of what had been loose material which was bound together by stalagmitic deposit. At the base of this were found a bone harpoon, a bone bead, and three flint flakes. Here, then, we have unmistakable evidence of a period when the cave was inhabited during an age long previous to that of the Roman time.
For the bone and stone implements were of the so-called Stone Age and had been buried by the rock debris which formed the floor on which the Roman accumulation had been built up.
The explorers now passed into the cave and found three deposits:
a. The upper cave-earth.
b. The laminated clay.
c. The lower cave-earth.
The two cave-earths look much alike, being formed of large and small limestone blocks intermingled with stiff clay and occasional beds of stalagmite.
In the upper cave-earth were found the bones of:
and it was concluded that man had used the cave as some of the bones were hacked. The presence of the reindeer shows that the climate was cold.
In the laminated clay no remains were found, but in the lower cave-earth were found the bones of:
The chief layer in which these bones are found is a layer of occupation by the hyaena, whose dung is abundant. In fact, the cave was then a hyaena den, and into it the animals dragged portions of the carcasses of large animals and the whole bodies of small ones in order to devour them at leisure. The bones are frequently gnawed and cracked.
Although a human bone has been found in this layer it cannot be regarded as a proof that the cave was used as a human habitation during this period, but one may conclude that he lived in this district of Yorkshire at this time. This assemblage of animals points to a tolerably warm climate, for the hippopotamus and the hyaena required a considerable degree of warmth, the mammoth and rhinoceros also lived in warm countries, while the other animals are such as can adapt themselves to a wide range of temperature or generally live in temperate regions.
The story of even a single cave, when carefully unraveled, is therefore far from a simple one. It consists of a series of chapters which tell of very different conditions. In the case of this cave the first chapter tells of great warmth when man was living in the country and wild beasts, now no longer known in our islands, roamed at large.
The cave- loving hyaena used it for his den and so preserved for after ages the bones of his prey. Then follows a chapter dark with mystery and so far not deciphered. The waters came into the cave washing in the laminated clay, which is usually about 8 feet thick. In the next chapter we once more get much information; it tells us of quite a different inhabitant and quite different surroundings.
Gone is the hyaena, and with him the high-temperature animals, such as the hippopotamus, elephant, and rhinoceros; the country round is now no longer under almost tropical but under almost Arctic conditions; the reindeer browses where the elephant roamed. Man uses the cave, but we find that during his use of it he was in contact with animals which we no longer find in Yorkshire or in any of our islands.
Then in another chapter we get a glimpse of a stage of civilisation, when man used flint implements and made bone ones as well. And lastly, we get a good deal of information about the inhabiting of the cave in a period close to the fifth century.
The Kirkdale Cave, also in Yorkshire, has yielded remains of at least 500 hyaenas, and besides these bones of wolves, bears, cave-lions, Irish elks, bisons, and other animals. But the story of one cave is very much the story of all; with one exception, the animals which first inhabited them belong to the Pleistocene period, and in many cases what was a dwelling-place for the animal of that early time continued to be inhabited in the Historic period.
Since these caves have been such excellent places for the preservation of the remains of Pleistocene animals, one would at first thought expect to find older caves with the remains of the animals which inhabited Britain in the previous Pliocene period. The limestone range of the Pennines was above the sea in both periods; the water of the earlier period must have produced these caverns in the limestone in just the same way as it did later on, and one can see no reason to doubt that these caverns were inhabited by den-living animals.
7. Essay on the Buxton Cave:
Yet with the solitary exception of a cavern at Doveholes, near Buxton, not a single one of Pliocene age has been found in our islands. Here a large quarry in the Carboniferous limestone has been worked for years, and it was the chance discovery by a boy when rambling over the quarry with other boys that first called attention to this unique cave.
He happened to pick up in the quarry a tooth, which turned out to have belonged to a mastodon, a kind of elephant which had two tusks in its upper and two in its lower jaw.
Further investigation brought to light a very remarkable series of animal remains. The rare sabre-toothed tiger, which had two long down-curving large teeth coming out from the upper jaw, was discovered, also bones of the cave- lion, the hyaena, the mastodon, the elephant, the rhinoceros, the horse, and deer.
Investigation showed that the bones were commonly gnawed, even those of the fierce sabre-toothed tiger, and it was considered that they were washed out of some hyaena den down into lower chambers of the original cave.
The discovery of this cave opens up a very interesting enquiry. If there were caves in the Pliocene period, what has happened to them?
In Upper Pliocene times the British Isles were in every probability united together and to the north of France. The Pennine Chain ran up the middle of Yorkshire containing, no doubt, plenty of caverns in which animals lived and died, and into which the bones of their prey were brought.
Then came the Pleistocene period with its cold, its snow, and its ice. Denudation went on and removed from the top of the Pennines many hundreds of feet of rocks, and so the caves and their contents vanished. According to Professor Boyd Dawkins, at Doveholes at least 330 feet of rock must have been removed.
Denudation then is the cause of the non-existence now of Pliocene caves. In only one fortunate spot has the last termination of such a cave been found, but of course some more may yet be discovered.
It has been mentioned that some caves have been found to contain the remains of men. The type of man that lived in them was very primitive, and his weapons and tools were chiefly of flint.
In France, however, a somewhat superior race existed, for in some French caves there have been found, not only the implements of this early man, but also some examples of his artistic efforts. On some of the bones found in these caves he has scratched pictures of the mammoth and the elk, so that we have perfect evidence that these animals were living when early man inhabited Europe.