Analysis of Sonnet 09

I know not why, but all this weary day,
Suggested by no definite grief or pain,
Sad fancies have been flitting through my brain;
Now it has been a vessel losing way,
Rounding a stormy headland; now a gray
Dull waste of clouds above a wintry main;
And then, a banner, drooping in the rain,
And meadows beaten into bloody clay.
Strolling at random with this shadowy woe
At heart, I chanced to wander hither! Lo!
A league of desolate marsh-land, with its lush,
Hot grasses in a noisome, tide-left bed,
And faint, warm airs, that nestle in the hush,
Like whispers round the body of the dead!