[CHAPTER III.]
THE EXTERNAL FEATURES OF THE CAVES.
That portion of the limestone dyke in which the caves are found runs six miles north and south; and the Grand Arch and the Devil's Coach House—the two principal "day caves"—are formed right through the mountain, near the centre, in an easterly and westerly direction. On the one side McEwan's Creek flows towards the Devil's Coach House, and on the other side is a natural watercourse leading to the Grand Arch, which is only a few yards distant from it. Bearing in mind how the watercourses converge towards these two central caves, and with what force, in times of heavy rain, the floods scour them, a good understanding may be obtained of the mechanical causes of the enormous excavations which excite amazement as well as admiration. If a visit be paid in winter, when the frost is sharp and the ground is "hoar with rime;" when every bough and every blade of grass is covered with congealed dew and adorned with forms of crystallisation which rival the rarest beauties of the caves; when rocks are split and crumbled by sudden alternations of heat and cold; there will be abundant illustration of the effect of water and light, and the variation of temperature in causing geological transformation. Limestone is not soluble in water without the addition of carbonic acid. An exploration of the caves, however, shows that the mountains are not composed entirely of limestone, but that other substances constitute part of their bulk. The principal causes of the formation of the "day caves," the Grand Arch and the Devil's Coach House, are the mechanical action of water and the variation of temperature. As regards the interior caves, where night reigns supreme, chemical combination has played a more important part. But the effect of water power is everywhere observable in graceful contours, caused by continuous motion, or in stony efflorescence, produced by intermittent humidity or dryness of the atmosphere. The action of the former is the more marked and striking, the latter more elaborate, and microscopically beautiful. The hygrometric condition of the caves is recorded in lovely forms, which lend enchantment to ornate bowers, sparkling grottoes, and fairy cities.
THE GRAND ARCH ENTRANCE.
THE GRAND ARCH—LOOKING EAST.
THE GRAND ARCH.
The Grand Arch runs east and west, and is about 150 yards in length, 60 feet high, and 70 feet wide at its western end. The eastern end is 80 feet high, and about 200 feet wide. Its proportions and outline are gloomily impressive, and rather awe-inspiring. It is like the portico to some great castle of Giant Despair. The eastern end is a marvel of natural architecture, and the wonder is how so spacious a roof can remain intact under a weight so enormous. The rugged walls are varied by many peculiar rocky formations. On the northern side is "the Lion," shaped in stone so as to form a fair representation of the monarch of the forest. "The Pulpit" and "the Organ Loft" are suggestive of portions of some grand old cathedral. Adjacent is "the Bacon Cave," where the formations represent "sides," like so many flitches in the shop of a dry salter. The roof is hung with enormous honeycombed masses of limestone, whose sombre shades deepen to blackness in numerous fissures and crannies and cavernous spaces. As seen from the floor the roof appears to be covered with rich bold tracery, engraved by Herculean hands. Near the basement are huge rocky projections, with deep recesses, which for ages have been the retreat of rock wallabies. Near the eastern entrance, lying on the ground, is a gigantic block of limestone, weighing from 1,500 to 2,000 tons, and which at some remote period fell, and tilted half over. This is evident from the stalactite formation which remains on it. Ascending the precipitous masses on the south-eastern side of the eastern entrance over rocks which are, on the upper surface, as smooth as glazed earthenware, a position is attained from which the magnitude of the ornaments of the roof can be estimated. It is then perceived that what, viewed from the floor of the archway, seemed like natural carving in moderately bold relief, are pendant bodies of matter extending downwards 10 to 15 feet, and of enormous bulk. Along the walls of the arch are caves running obliquely into the mountain 10, 15, and 20 feet, and the bottom of which is thick with wallaby "dust." Out of these caves are passages which enable the marsupials to pass from one rocky hall to another until they find a secure refuge in some obscure and sunless sanctuary. The wallaby dust resembles mosquito powder. Perhaps it would be equally efficacious. It is not improbable that the floors of these caves represent a moderate fortune. The explorer sinks over his boot tops in the fine pulverised matter, which, however, is not odoriferous, and is void of offence if a handkerchief be used as a respirator. The presence of this substance, and the oxidisation of its ammonia, probably account for the saltpetre in the crevices of adjacent rocks, although not absolutely necessary to the result, because, in the absence of such accessories, it is an admitted chemical fact that nitrifiable matter is not commonly absent from limestone. In the Mammoth Cave of Kentucky saltpetre manufacture was carried on to a great extent by lixiviation from 1812 to 1814, and during the Civil War a principal factor in the manufacture of gunpowder was obtained from the same source. Up amongst the rocks, midway between the floor and the roof of the eastern entrance to the Grand Arch, in the midst of the wallaby drives, and near to a haunt of the lyre bird, the present curator of the caves had his sleeping-place for 20 years. There he strewed his bed of rushes or of grasses and ferns and mosses; and certainly neither Philip Quarll nor Robinson Crusoe had ever a more magnificent dormitory.