That came out of my verse-detection program: I've tried it so far on LotR and Jane Austen's novels. Austen shows substantially less of the iambic pentameter, reaching 3 lines in only two places. Here's Elizabeth Bennett turning down Mr. Darcy's first marriage proposal:
. . . my forming any serious design.Tolkien produced many more hits -- the longest were all songs and poems, naturally (Ents have the most iambicity, followed by hobbits and everyone else). These verse bits gained a kind of polyrhythm from the pentameter -- being written for a different number of beats per line ("O rowan fair, upon your hair how white the blossom lay") -- and I wonder if anyone's consciously gone for that effect.
These bitter accusations might have been
Suppressed, had I, with greater policy,
Concealed my struggles. . .
The verse I quoted was the longest prose passage to come up (though the first few lines of it were not joined up by my program, with its rather robotically-strict idea of meter). In Tolkien's case at least I think this is no coincidence, this blank-versish prose showing up at a climax of the story. I wonder if it'd be fun to try to quantify that question over a bigger sample of fiction.
A couple more bits from this never-yet-seen Miltonic epic:
. . . He made the end fast round his waist, and then
He grasped the line with both hands. Sam stepped back
And braced his feet against a stump a yard
Or two from the edge. Half hauled, half scrambling,
Frodo came up and threw himself on the ground.
. . . I've got them both still. But lend them to me
A little longer, Mr. Frodo. I
Must go and see what I can find. You stay
Here. Walk about a bit and ease your legs.
I shan't be long. I shan't have to go far."
"Take care, Sam!" said Frodo. "And be quick!
(I extended these as well into the surrounding context where it didn't do too much violence to the meter.)