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. [Illustration: 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.