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Of these beds over beds it is still more remarkable, that each of them, as far as it extends, maintains exactly the same thickness. It is found, also, that, as we proceed to considerable depths, every layer grows thicker. They are sometimes very extensive, being found often to cover a space of many leagues in circumference. But it must not be supposed, that they are uniformly continued over the whole globe, without interruption: on the contrary, they are ever, at small intervals, cracked through, as it were, by perpendicular fissures; the earth resembling, in this respect, the muddy bottom of a pond, whence the water has been dried off by the sun, and thus gaping in several chinks, which descend in a direction perpendicular to its surface. These fissures are many times found empty, but are often closed up by adventitious substances, which the rain or some other accidental causes, have conveyed to their cavities. Their openings are not less different than their contents, some being not above half an inch wide, some a foot, and some several yards asunder; which last form those dreadful chasms that are to be found in the Alps, at the edge of which the traveller stands, dreading to look down to the immeasurable gulf below. These amazing clefts are well known to such as have passed those mountains, where a chasm frequently appears several hundred feet deep, and as many over, at the edge of which way lies. It often happens also, that the roads lead along the bottom, and then the spectator observes, on each side, frightful precipices several hundred feet above him; the sides of which correspond so exactly with each other, that they seem evidently torn asunder.

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But the chasms in the Alps are nothing to what are to be seen in the Andes in America. These amazing mountains, in comparison of which the former are but little hills, have their fissures in pro

portion to their magnitude. In some places, they are a mile wide, and deep in proportion; and there are some others, that running under ground, resemble, in extent, a province'.

Of this kind also is the cavern called Elden Hole -in Derbyshire; which, Dr. Plott tells us, was sounded by a line of 2800 feet, without finding the bottom, or meeting with water; and yet the mouth of it is not above forty yards over. This immeasurable chasm runs vertically downward; and the sides of it seem to tally so correctly, as to show that they were once united. Those who visit the chasm generally procure stones to be thrown into its mouth; and these are heard for some time, falling and striking against its sides, producing a sound like distant thunder, dying away as the stone falls deeper.

There are many more of these dreadful perpendicular fissures in different parts of the Earth, with accounts of which Kircher, Gaffarellus, and others, who have given histories of the wonders of the subterranean world, abundantly supply us. The generality of readers, however, will consider them with less astonishment, when they are informed of their being common all over the Earth; that in every field, in every quarry, these fissures are to be found; either still gaping, or filled with matter that has accidentally closed their interstices. The inattentive spectator neglects the inquiry; but their being common is partly the cause that excites the philosopher's attention to them. The irregularities of Nature he is often content to pass over unexamined; but when a constant and common appear ance is presented, every return of the object is a fresh call to his curiosity, and the chink in the next. quarry becomes as great a matter of wonder as the

Goldsmith's History of the Earth, vol. i. ch. 6..
Philosophical Transactions, vol. ii. page 370.

chasm in Elden Hole. Philosophers, therefore, have long endeavoured to find out the cause of these vertical fissures, which our own countrymen, Woodward and Ray, were the first who observed to be so common and universal. Buffon supposes them to be cracks made by the sun, in drying up the earth, immediately after its emerging from the deep. The heat of the sun is very probably a principal cause; but it is not right to ascribe to one cause only, what we find may be the result of many causes. Earthquakes, severe frosts, bursting waters, and storms tearing up the roots of trees, have produced them in our own times; and to this variety of causes we must, at present, be content to ascribe those which have happened at remote periods, before we could have the opportunity of making any observations upon them.

But in surveying the subterranean wonders of the globe, beside those fissures that descend vertically, we frequently find others that descend but a little way, and then spread themselves often to a great extent below the surface. Many of these caverns, it must be confessed, may be the production of human art and industry; retreats made to protect the oppressed or shelter the robber. Such, for instance, are the famous labyrinths of Candia; the stone quarry of Maestricht; the salt mines in Poland; some of the catacombs in Egypt and Italy; and a great number of artificial caverns in Spain, that were made to serve as retreats for the Christians against the fury of the Moors. But the greatest number of caverns have been fashioned by the hand of Nature only. Indeed, there is scarcely a country in the world without its natural caverns; and, every day, many new ones are discovered. Of those in England, Oakey-hole in Somersetshire, the Devil'shole in Derbyshire, and Penmark-hole in Gloucestershire, have been often described. The former.

lies on the south side of Mendip-hills, about a mile from the city of Wells. To conceive a just idea of this, we must imagine a precipice of more than one hundred yards high, on the side of a mountain, which shelves away a mile above it. In this is an opening not very large, into which we enter, going along upon a rocky uneven pavement, sometimes ascending, and sometimes descending. The roof of it, as we advance, grows higher, and, in some places, is fifty feet from the floor. In some places, however, it is so low, that a man must stoop to pass. It extends, in length, about two hundred yards; and from every part of the roof, and the floor, there are formed sparry concretions of various figures, which by strong imaginations have been likened to men, lions, and organs. At the farthest part of this cavern rises a stream of water, well stored with fish, large enough to turn a mill, and discharging itself at the entrance.-But of all the subterranean caverns now known, the most remarkable is the Grotto of Antiparos, discovered in the island of that name, by Magni, an Italian traveller. The descriptions of this, by Kircher, Tournefort, and the count de Choiseul Gouffier, are too long to be inserted, but are highly deserving the attention of the inquisitive traveller, who visits these subterraneous scenes for amusement only, and the more minute observation of the philosopher, ardent to pursue Nature to her

most secret recesses.

It is here natural to inquire how these amazing hollows of the earth came to be formed. It seems evident to a philosopher who would attend to the account of Oakey-hole, and to the descriptions that have been given of the other caverns I have mentioned, that their excavation has been occasioned by streams of water; which finding subterranean passages, and by degrees hollowing the beds in which they flowed, the ground above them has slipped

down closer to their surface, leaving the upper layers of the earth or stone still suspended: the ground that sunk upon the face of the waters forming the floor of the cavern; the ground, or rock, that kept suspended, forming the roof. Indeed, there are but few of these caverns found without water, either within them, or near enough to point out their formation.

No. LXXIV.

ON EXTRANEOUS FOSSILS,

There are more things in heaven and earth
Than are dreamt of in our philosophy.

SHAKSPEARE.

THE origin of greater part of the subterranean curiosities is involved in such impenetrable obscurity, that the philosopher, in his most profound reasonings, as well as the poet, in his ideal excursions, may justly imagine, that creation at large abounds with innumerable objects, of which the most laborious inquirers into nature have hitherto formed no conception. Among these subterranean wonders, that division of fossils which is denominated extraneous, has employed the curiosity of several of our latest naturalists.

The word Fossil is used, in a general sense, for any thing dug out of the Earth, as metals, stones, salts, earths, and other minerals, which are called native fossils; or for any thing deposited in the bowels of the Earth, by any extraordinary means,

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