The land's sharp features seemed to beThe Century's corpse outleant, (9-10)
What's scarier than death? Seriously, folks. And the over-the-topness of this description only makes it more chilling.
The ancient pulse of germ and birthWas shrunken hard and dry, (13-14)
Nature's gone crazy. In the speaker's mind, even birth and regeneration is no longer possible. Then again, have you ever known a winter that wasn't followed by spring at some point? Exactly. Maybe it's not as hopeless and scary as it appears.
And every spirit upon the earthSeemed fervourless as I. (15-16)
"Fervourless" spirits can't have enough energy to be scared. But the depiction of zombie-like people is supposed to strike fear into the hearts of any and all readers.