GROTTO, a large deep cavern or den in a mountain or rock. Okey-hole, Elden hound, Peake's-hole, and Pool's-hole, are famous among the natural caverns or grottoes of our country. The entrance to Okey.hole, on the south side of Mendip hills, is in the fall of those hills, which is beset all about with rocks, and has near it a precipitate descent of near twelve fa thoms deep, at the bottom of which there continually issues from the rocks a con siderable current of water. The naked rocks above the entrance she w themselves about thirty fathoms high, and the whole ascent of the hill above is about a mile, and is very steep. As you pass into this vault, you go at first upon a level, but ad vancing farther, the way is found to be rocky and uneven, sometimes ascending and sometimes descending. The roof of this cavern, in the highest part, is about eight fathoms from the ground, but in ma ny particular places it is so low that aman must stoop to get along. The breadth is not less various than the height, for in some places it is five or six fathoms wide, and in others not more than one or two. It extends itself in length, about two hun dred yards. People talk much.of certain stones in it resembling men and women, and other things ; but there is little mat ter of curiosity in these, being only shape less lumps of a common spar. At the far thest part of the cavern there is a good stream of water, large enough to drive a mill, which passes all alongone side of the cavern, and at length slides down about six or eight fathoms among the rocks, and then passing through the clefts of them, discharges itself into the valley. The river within the cavern is well stored with eels, and has some trout in it ; and these cannot have come from without, there be ing so great a fall near the entrance. In dry summers, a great number of frogs are seen along this cavern, even to the farthest part of it; and on the roof of it, at certain places, hang vast numbers of bats, as they do in almost all caverns, the entrance of which is either level, or but slightly as cending or descending ; and even in the more perpendicular ones they are some times found, provided they are not too narrow, and are sufficiently high. The cattle that feed inthe pastures through which this river runs have been known to die suddenly sometimes after a food; this is probably owing to the waters having been impregnated, either naturally or ac cidentally, with lead ore.
Elden-hole is a huge profound perpen dicular chasm, three miles from Buxton, ranked among the natural wonders of the Peak. Its depth is unknown, as it is pre tended to be unfathomable.
Peake's-hole, and Pool's-hole, are two remarkable horizontal cavities under mountains ; the one near Castleton, the other just by Buxton. They seem to have owed their origin to the springs which have their current through them ; when the water had forced its way throughthe horizontal fissures of the strata, and had carried the loose earth away with it, the loose stones must fall down of course: and where the strata had few or no fissures, they remained entire; and so formedthese very irregular arches, which are now so much wondered at. The water which
passes through Pool's-hole is impregnat ed with particles of lime-stone, and has incrusted the whole cavern in such a man ner that it appears as one solid rock.
Grotto del Cani, is a little cavern near Pozzuoli, four leagues from Naples; the air contained in it is of a mephitical or noxious quality ; it is in truth carbonic acid gas, whence also it is called Bocca Venenosa, the poisonous mouth. Two miles from Naples, (says Dr. Mead,) just by the Lago de Agnano, is a celebrated mofeta, commonly called la Grotta del Cani, and equally destructive to all within the reach of its vapours. It is a small grotto about eight feet high, twelve long, and six broad ; from the ground arises a thin, subtile, warm fume, visible enough to a discerning eye, which does not spring up in little parcels here and there, but in one continued stream, covering the whole surface of the bottom of the cave ; having this remarkable difference from common vapours,that it does not, like smoke, dis perse itself into the air, but quickly after its rise falls back again, and returns to the earth ; the colour of the sides of the grot to being the measure of its ascent: for so far it is of a darkish-green,but higher,only common earth. And as I myself found no inconvenience by standing in it, so no ani mal, if its head is above this mark, is the least injured. But when, as the manner is, a dog, or any other creature, is forcibly kept below it, or, by reason of its small, ness, cannot hold its head above it, it pre sently lose* all motion, falls down as dead, or in a swoon, the limbs convulsed and trembling, till at last no more signs of life appear, than a very weak and almost insensible beating of the heart and arte ries ; which, if the animal is left a little longer, quickly ceases too, and then the case is irrevocable ; but if it is snatched out and laid in the open air, it soon comes to life again, and sooner if thrown into the adjacent lake." GnoTTo is also used for a small artificial edifice made in a garden, in imitation of a natural grotto.
The outsides of' these grottoes are usu ally adorned with rustic architecture, and theirinside with shell-work, coral, &c.and also furnished with various fountains, and other ornaments.
The following is recommended as good cement for grotto work. Take two parts of white resin, melt it clear, add to it four parts of be es'-wax; when melted together, add some flower of the stone you design to cement, two or three parts, or so much as will give the cement the colour of the stone; to this add one part of the flower of sulphur : first incorporate all together over a gentle fire, and afterwards knead it with your hands in warm water. With this fasten the stones, shells, &c. after they are well dried, and warmed before the fire.