Wordsworth has described a more personal experience which
chimes in with all that has been said.

"Through a rift
Not distant from the shore on which we stood,
A fixed, abysmal, gloomy, breathing place--
Mounted the roar of waters, torrents, streams
Innumerable, roaring with one voice!
Heard over earth and sea, and, in that hour,
For so it seemed, felt by the starry heavens."

If the modern poet could be thus affected, how much more the
primitive man who looked down on water falling into chasms,
or rushing through their depths. It was natural that such
experiences should find expression in his systems of
mythology. The general form they assume is that of springs and
rivers in the underworld, the best known of which appear in the
Graeco-Roman conceptions of Hades. Homer makes Circe
direct Odysseus thus. He is to beach his ship by deep-eddying
Oceanus, in the gloomy Cimmerian land. "But go thyself
to the dank house of Hades. Thereby into Acheron flow
Pyriphlegethon and Cocytus, a branch of the water of the Styx,
and there is a rock and the meeting of the two roaring waters."

Such were the materials which, with many additions and
modifications, developed into the Hades of Virgil's sixth
AEneid, with its lakes, and swamps and dismal streams. The
subterranean waters figured also in the Greek mysteries, and are
elaborated with much detail in Plato's great Phaedo Myth--in all