Lines 8-12 Summary

Get out the microscope, because we’re going through this poem line-by-line.

And then a Quarry pare

To fit its Ribs
And crawl between

Now the train "crawls" through a narrow tunnel or passage in the mountainous terrain.
Some of the words here are a bit strange, so we'll help you out.
"Pare" is a word you've probably heard before. Ever used a "paring knife" to "pare" (cut) up a piece of fruit?
"Quarry" is a place where stone is cut from the ground.
"Ribs" seems to be a metaphor for the train tracks—can't you picture the resemblance?
"Paring" a "quarry" makes it sound as though the thing slices through rock as effortlessly as a knife through an apple.
Of course, it probably wasn't quite that easy to cut away the rocks for the train. But you get the idea.

Complaining all the while
In horrid — hooting stanza —

The mystery creature whines horribly as it moves through the rock, making a loud ruckus.
What did we tell you about the personification in this poem? By describing it as "complaining," the speaker gives the train even more personality.
Check out the use of the word "stanza." It makes us think of stanzas of poetry, which have a rhythmic quality. It seems like the horrible sounds coming from this thing are rhythmic, too.