It’s not just a matter of compression, in the information-theory sense, but of scaling the print narrative down (or up, in the case of books like Polar Express that are shorter than the film) so that it preserves the structuring relationships of the story despite playing out much more quickly.

I have no doubt the Land of the Dead sequence will appear in the film version of Amber Spyglass — it’s too central to the scaffolding — but it can’t possibly work the same way it does in the book, because the power of the sequence stems largely from its duration. And duration is the one thing that always gets sacrificed in a scaling-down between one medium (print) with time to burn and another (cinema) in which time equals resources equals money. When film does invoke the durative dimension as a device, it’s as a stunt (the long, dialogueless sequence of Tom Hanks stranded on his island in Castaway), an auteurist display (most of Stanley Kubrick’s movies and key moments in many of Hitchcock’s, DePalma’s, and Scorsese’s), or an intentional rupture that marks the film as avant-garde, experimental, political (Andy Warhol, Chantal Akerman).

Sequences like Land of the Dead or Minas Tirith that are great partly because they force us to spend time with them always suffer in the conversion to film. We can never shake the sense, watching the action race by, that something has been excised. But more significantly, the short-sequence-pretending-to-be-long reminds us fatally of the presence of a competing authorial “system” (composed not just of director and screenwriter, of course, but of cinematographer, editor, up and up the ladder to the studio and market forces that combine to select what pieces of a beloved narrative will make it intact to the screen). We’re suddenly cast in a new role — not just spectator but arbiter, judge, defense attorney, a whole mental courtroom in which we debate the merits of the print author’s vision versus the film author’s.

This for me is part of the issue: when do filmmakers blow something that’s cinematic that’s standing right in front of them? I was kind of gobsmacked by Jackson’s version of the sequence at the gates of Minas Tirith in comparison to Tolkien’s in ROTK. Because Tolkien’s is already wonderfully cinematic: it’s practically a screenplay. The forces of Mordor fight at the walls. They break into the final major gate. Grond is used to break the gates. We have the drama of Faramir’s potential burning happening elsewhere, intercut. The gate breaks. Gandalf is alone at the gates, in rides the Witch-King. They are about to have a confrontation, but you get a sense that it is going to go very badly for Gandalf if so.

Then the horns of Rohan ring out. The Witch-King flies off. Pippen runs up to tell Gandalf about Faramir. Great dramatic choice: pursue the Witch-King, lead the fight out onto the fields, or save Faramir?

Jackson muddled that sequence up in both the theatrical and the extended version. In most cases, the changes he put in made great cinematic sense and great narrative sense. In dramatic terms, his Aragorn is way more interesting than Mr. Noble Destiny in Tolkien. But in this case, you scratch your head and say, WTF?

I think that’s the interesting question in adaptation generally, and it’s an old one. Maybe it takes on some special elements when fantasy is involved, I suppose.