It’s by far my favorite Stephenson book.

When the climate had been warmer, civilizations had sloshed back and forth across this glacier-planed landscape for a couple of thousand years like silt in a miner’s pan, forming drifts of built-up stuff that stayed long after the people had departed. At any given moment during those millennia, a billion might have lived on this territory that now supported a few tens of thousands. How many bodies were buried up here, how many people’s ashes scattered? Ten, twenty, fifty billion all told? Given that they all used electricity, how many miles of copper wire had been sewn through their buildings and under their pavements? How many man-years had been devoted to the one activity of pulling and stapling those wires into place? If one out of a thousand was an electrician, something like a billion man-years had been devoted to running wire from one point to another. After the weather had grown cold again and the civilizations had, over the course of a few centuries, shifted south—moving like glaciers—scavengers had begun coming up here to undo those billion man-years one tedious hour at a time, and retrieve those countless miles of wire yard by yard. Professional scavengers working on an industrial scale had gotten ninety percent of it quickly. I’d seen pictures of factories on tank treads that rolled across the north and engulfed whole city blocks at a time, treating the fabric of the ruins just as a mining robot would an ore-rich hill, grinding the buildings to rubble and sorting the shards according to density. The first ruins we had seen were the feces that those machines left along their paths.

Stripping ruins by hand was more expensive. When times were prosperous elsewhere, metals became precious enough that miners could make a life out of venturing to the deep ruins—far-flung cities of old, never reached by the factories-on-tank-treads—and extracting whatever was most valuable: copper wires, steel beams, plumbing, or what have you.

I very much hope the Western environmentalists don’t start pushing for this as mandatory.