In the Azure Cave of Capri, the Mediterranean possesses a marine grotto rivalling Fingal’s Cave in celebrity, and no less wonderful in its peculiar style of beauty. As the roof of its narrow entrance rises only a few feet above the level of the sea, it is probable that no human eye had ever been delighted with its charms before 1826, when it was accidentally discovered by two Prussian artists who were swimming in the neighbourhood. After passing the low portal the cave widens to grand proportions, 125 feet long and 145 feet broad, and except a small landing-place on a projecting rock at the further end, its precipitous walls are on all sides bathed by the influx of the waters, which, in that sea, are so clear that the smallest objects may be distinctly seen on the bottom of the deep basin, the most beautiful bathing-place a mermaid might wish for. All the light that enters the grotto must first penetrate the whole depth of the waters before it can be reflected into the cave, and it thus acquires so blue a tinge, from the large body of clear water through which it has passed, that the walls of the cavern are illumined by a radiance of the purest azure. Had Byron known of the existence of this magic cave, Childe Harold would surely have devoted some of his most brilliant stanzas to its praise.
In many other parts of the Mediterranean the limestone rocks that fringe its shores have been worn into magnificent caverns, less singular, indeed, than the fairy grot of Capri, but still of rare and wonderful beauty. Such, among others, is the Antro di Nettuno, in the island of Sardinia, about twelve miles from the small seaport of Alghero.[[14]]
Exceedingly picturesque caverns have also been worn by the chafing waters in the chalk cliffs under Bonifacio, in the island of Corsica. Their entrances festooned with hanging boughs, they penetrate far into the interior of the rocks, and the water percolating through their vaulted roofs has formed stalactites of fantastic shapes. The boat glides through the arched entrance, and the glaring sunshine without is replaced by cool and grateful shade. Fishes are flitting in the clear water; limpid streams oozing through the rocks form crystal basins with pebbly bottoms; and the channels from the blue sea, flowing over the chalk, become cerulean. Poetic fancy has never pictured anything more enchanting than these lovely caves.
CAVE UNDER BONIFACIO.
The rocky coast of Sicily is likewise hollowed out with numerous marine grottoes, which, though rarely noticed by travellers, may well be ranked amongst the greatest natural beauties of the island. One of the most remarkable is the Grotta di Nettuno, near Syracuse, which, in calm weather, admits a boat to a considerable distance. Its rugged vaults rise to a height of about twenty or thirty feet, and are covered with stalactites wherever the water does not reach. There is no landing-place, and throughout the whole cave the water is as deep as in the open sea beyond. Nothing can be more charming than to look back from the dark recesses of the grotto upon the bright sunshine without, and to listen to the soothing murmurs of the clear waves as they ripple against the rocky walls. The atmosphere is so pure in this delicious climate that not a trace of fog or mist obscures even the remotest parts of the cave, and the serene daylight falling through the entrance renders even its deepest shadows translucent. Here a lover of nature might linger for hours enjoying the most delicious coolness, and watching the charming effects of light and shade in their ever-varying play.
On many rocky shores the ocean has worn out subterranean channels in the cliffs, against which it has been beating for ages, and then frequently emerges in water-spouts, or fountains, from the opposite end. Thus in the Skerries, one of the Shetland Islands, a deep chasm or inlet, which is open overhead, is continued underground, and then again opens to the sky in the middle of the island. When the tide is high, the waves rise up through this inland aperture, with a noise like the blowing of a whale.
Similar phenomena occur on the south side of the Mauritius,[[15]] on the north coast of Newfoundland, near Huatulco on the Mexican coast of the Pacific, and near Peniscola, in Spain, where a cave, through whose roof at storm tides the sea bursts with a terrific noise, has received the name of the ‘Bufador, or the water-spout of Pope Luna,’ the family name of Benedict XIII., who, having been deposed by the Councils of Pisa and Constance, retired to the small Spanish town where he was born. As the chief occupation of the holy father in exile was to vent a continuous torrent of curses and excommunications upon his numerous enemies, it is probable that this circumstance caused his name to be given to the noisy but harmless Bufador.
Though water, aided by time, is probably the chief excavating power, there can be no doubt that the action of subterranean fire has likewise produced, and still produces, many hollows in the hard crust of the earth. Wherever a volcano has been piled up to the skies, the matter ejected from its vents must necessarily have left a void behind, and given rise to corresponding cavities in the space beneath. The shock of an earthquake must frequently rend asunder deep-seated rocks, and the slow upheaval of considerable tracts of land can hardly be supposed to take place without the formation of hollows and crevices.
When the lavas poured forth during an eruption are in a liquid state, they do not form on cooling a compact homogeneous mass, but generally exhibit a porous, spongy texture, due to the bubbles of the vapour generated through, or entangled in, their mass. These bubbles frequently unite in larger volumes, which, influenced by their elasticity and inferior specific gravity, rise towards the surface of the lava as it flows on, and, when sufficiently powerful, raise its crust in dome-like or conical protuberances, which not seldom burst open at the summit, or crack at the sides. The hollows thus formed are often so large as to entitle them to the name of caves.