To Winter

(since clearly my hope for spring was in vain)

O winter! bar thine adamantine doors:
The north is thine; there hast thou built thy dark
Deep-founded habitation. Shake not thy roofs
Nor bend thy pillars with thine iron car.

He hears me not, but o’er the yawning deep
Rides heavy; his storms are unchain’d, sheathed
In ribbed steel; I dare not lift mine eyes;
For he hath rear’d his sceptre o’er the world.

Lo! now the direful monster, whose skin clings
To his strong bones, strides o’er the groaning rocks:
He withers all in silence, and in his hand
Unclothes the earth, and freezes up frail life.

He takes his seat upon the cliffs, the mariner
Cries in vain. Poor little wretch! that deal’st
With storms, till heaven smiles, and the monster
Is driven yelling to his caves beneath Mount Hecla.

That's William Blake. And I love it, but if someone could explain the meter in the last stanza to me, I would be obliged.