I never brushed aside the leaves That stemmed a mountain spring But came the shadow of a dread Age-old unreasoning, That I had turned my helpless back To claws that followed on my track.
I never crossed the bar at dawn Where waves rose thin and green And watched an old seal close aboard, Distorted by the screen, But grim Cerberus stood once more And growled before the nether door!
Two quiet moments from nature open this short poem. In the first, the speaker pushes aside leaves to reach a mountain spring; in the second, he stands at dawn by a green, thin-looking wave and watches an old seal through the water. Both scenes sound peaceful, even lovely. Yet each time, something dark slips in. A "dread" arrives, an "age-old unreasoning" fear that he has turned his back on claws following him.
The second stanza names the feeling more boldly by calling up Cerberus, the monstrous dog of Greek myth who guards the entrance to the underworld. The "nether door" suggests death or the unknown, waiting just beneath ordinary life.
What the speaker feels is a kind of shiver he can't explain, and the poem doesn't try to. Calling the fear "unreasoning" admits it makes no sense. The mood is uneasy and hushed: nature is beautiful, but it carries an ancient, instinctive sense that something is watching from the shadows.