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