imagination takes wings to itself; images rise up before him,
and, without conscious effort, find verbal equivalents. The
enduring substance of the vision is embodied in the fragment,
"Kubla Khan," the glamour of which depends chiefly on the
mystical appeal of subterranean waters. We are transported to
where

"Alph, the sacred river, ran
Through caverns measureless to man,
Down to a sunless sea."

These three lines make a deeper impression than any others in
the poem, and form its main theme.

Nor is the feeling of the supernatural unrecognised. Spirits are
near with prophetic promptings. From a deep chasm the sacred
river throws up a mighty fountain, and for a short space
wanders through wood and dale, only to plunge again into its
measureless caverns, and sink in tumult to a lifeless ocean:

"And mid this tumult Kubla heard from far
Ancestral voices prophesying war."

Thus when Coleridge's imagination was set free, the mode of
feeling declared itself which had persisted down the ages to the
present. The primitive experience is there in its essentials,
enriched by the aesthetic and intellectual gains of the
intervening centuries. Doubtless there is a living idea, or rather
a group of living ideas, behind the phenomena of subterranean
waters.