From the fabulous blog, Brainpickings.

MARGINALIA by BILLY COLLINS

Sometimes the notes are ferocious,
skirmishes against the author
raging along the borders of every page
in tiny black script.
If I could just get my hands on you,
Kierkegaard, or Conor Cruise O’Brien,
they seem to say,
I would bolt the door and beat some logic into your head.

Other comments are more offhand, dismissive –
“Nonsense.” “Please!” “HA!!” –
that kind of thing.
I remember once looking up from my reading,
my thumb as a bookmark,
trying to imagine what the person must look like
who wrote “Don’t be a ninny”
alongside a paragraph in The Life of Emily Dickinson.

Students are more modest
needing to leave only their splayed footprints
along the shore of the page.
One scrawls “Metaphor” next to a stanza of Eliot’s.
Another notes the presence of “Irony”
fifty times outside the paragraphs of A Modest Proposal.

Or they are fans who cheer from the empty bleachers,
Hands cupped around their mouths.
“Absolutely,” they shout
to Duns Scotus and James Baldwin.
“Yes.” “Bull’s-eye.” “My man!”
Check marks, asterisks, and exclamation points
rain down along the sidelines.

And if you have managed to graduate from college
without ever having written “Man vs. Nature”
in a margin, perhaps now
is the time to take one step forward.

We have all seized the white perimeter as our own
and reached for a pen if only to show
we did not just laze in an armchair turning pages;
we pressed a thought into the wayside,
planted an impression along the verge.

Even Irish monks in their cold scriptoria
jotted along the borders of the Gospels
brief asides about the pains of copying,
a bird singing near their window,
or the sunlight that illuminated their page –
anonymous men catching a ride into the future
on a vessel more lasting than themselves.

And you have not read Joshua Reynolds,
they say, until you have read him
enwreathed with Blake’s furious scribbling.

Yet the one I think of most often,
the one that dangles from me like a locket,
was written in the copy of Catcher in the Rye
I borrowed from the local library
one slow, hot summer.
I was just beginning high school then,
reading books on a davenport in my parents’ living room,
and I cannot tell you
how vastly my loneliness was deepened,
how poignant and amplified the world before me seemed,
when I found on one page

A few greasy looking smears
and next to them, written in soft pencil –
by a beautiful girl, I could tell,
whom I would never meet –
“Pardon the egg salad stains, but I’m in love.”