effectively as those which ascended and descended at will in the subterranean world inhabited by "the coming race." It was, perhaps, some such place as this which suggested to Bulwer Lytton the chasm down which his nameless hero descended to the bottom of an abyss illuminated with a diffused atmospheric light, soft and silvery as from a northern star; where he found lakes and rivulets which seemed to have been curbed into artificial banks, some of pure water, and some which shone like pools of naphtha; where the birds piped in chorus, and where he made the acquaintance of the An people and the Gy-ei, who moved through the air without effort, who had for servants automata always obedient, and totally ignorant of the eight-hours system, and whose religion had these two peculiarities: "Firstly, that they all believed in the creed they professed; and, secondly, that they all practised the precepts indicated by the creed." Underground rivers appear to be natural to limestone caves. The reason of their existence is to be found in the fact that the mountains in which they are formed are, in geological parlance, "dykes." They must not be confounded with old river beds, such as are encountered by miners--where the surface of the earth has been raised by deposits of alluvium, or where the geological condition of things has been changed by volcanic action. These cave rivers have all been formed by water finding the lowest attainable level in its passage to the sea, and by the solid limestone rocks which have barred its direct course, and have been undermined by its subtle but persistent action. The fluid, dammed back by the mountains, has simply obeyed the laws of gravitation and accumulated force, as evidenced in the trickling silvery thread which follows the course of ant-tracks; in the laughing rill which makes its bed among the pebbles; in the babbling brook which leaps to the swelling river; and in the mighty torrent whose strength and velocity proclaim the majesty of hydraulic power. In all parts of the world where limestone dykes and caves exist, it is reasonable to expect to find subterranean rivers. The eye of the seer can follow the water drips-- "Down through caverns and gulfs profound, To the dreary fountain-head Of lakes and rivers underground." He can see them again when the rain is done-- "On the bridge of colours seven, Climbing up once more to heaven, Past the setting sun." But the underground rivers found in caves perform vagaries outside the sweet imaginings of the poet and the prevision of the seer. Far from the beaten track they turbulently force their way through recesses and tunnels and pockets of the earth, before they are again warmed with sunshine, and glow in the harmonious colours which form the Bow of Promise.