The First Book of Urizen

7. And a roof vast, petrific around
On all sides he fram'd, like a womb,
Where thousands of rivers in veins
Of blood pour down the mountains to cool
The eternal fires, beating without
From Eternals; & like a black globe,
View'd by sons of Eternity standing
On the shore of the infinite ocean,
Like a human heart, strugling & beating,
The vast world of Urizen appear'd.