To that still roaring dell, of which I told; The roaring dell, o'erwooded, narrow, deep, And only speckled by the mid-day sun; (9-11)
His friends enter the valley around mid-day, with the sunlight passing down directly through the branches. The forest is so dense that only some of the light makes it through to the ground.
With some fair bark, perhaps, whose sails light up The slip of smooth clear blue betwixt two Isles Of purple shadow! (25-27)
This poem has many images of objects being "lit up" by afternoon or evening light. Think of all the leaves and trees that are illuminated. The light on the sails contrasts with the "purple shadow" of the islands. The sails just catch the last bit of daylight.
Ah! slowly sink Behind the western ridge, thou glorious Sun! (33-34)
The sunset forms the climax of the second stanza. All human activity in the poem ceases at this point as Charles is "struck" by the profound and transient beauty.
Pale beneath the blaze Hung the transparent foliage; and I watch'd Some broad and sunny leaf, and loved to see The shadow of the leaf and stem above Dappling its sunshine! And that walnut-tree Was richly ting'd, and a deep radiance lay Full on the ancient ivy, which usurps Those fronting elms, and now with blackest mass Makes their dark branches gleam a lighter hue Through the late twilight: and though now the bat Wheels silent by, and not a swallow twitters, Yet still the solitary humble-bee Sings in the bean-flower! (49-60)
This passage of the poem plays out the change of time that has been playing out throughout the poem as a whole. Using the imagery of light on leaves, the passage moves from full sunlight to "late twilight." You can also notice another pattern here: the emphasis on the "last" things of the day. Here we see the "last" bee in the flowers.
when the last rook Beat its straight path along the dusky air Homewards, I blessed it! deeming its black wing (Now a dim speck, now vanishing in light) (70-73)
And now here's the "last" bird or rook. As we have seen above, the birds have mostly been replaced by bats. The rook turns into a black speck as it flies into the last bit of light left from the sunset. For a similar image of birds flying at sunset, check out "Sunday Morning" by the American poet Wallace Stevens, also on Shmoop.