To conceive of the history of these millennia, you have to reset the chronometers of your imagination, and to think in ice-time and in tree-time. You have to imagine the air temperature rising over years. The fall of heavy warm rain on the gray backs of the glaciers. The blue glacial prows that marked the outworks of the ice, some of them hundreds of feet high, beginning their northwards retreat. The noise of those centuries, near the frontline of the glaciers, would have been prodigious: the screams of rending ice, the roars of calving ice (93).