Here's two sets of lines from the poem
"Thy Wind, thy wide grey skies!
Thy mist that roll and rise!"
Alliteration means that a set of words or closely connected words end in the same sound or letter. Which words?
"Skies"
"Rise"
An even better example is
"Thy woods, this autumn day, that ache and sag
And all but cry with colour! That gaunt crag "
"Sag"
"Crag"
You didn't list any examples but Hope that helps!