In years since he has rarely gone back to those old memories. As he does now, in the tavern near Harvard College, he's startled to find that the muddy whirl has been swept away. The mental pan has been churning for fifty years, sorting the dirt and sand to the periphery and throwing it off. Most of the memories are simply gone. All that remain are a few wee nuggets. It's not plain to Daniel why these impressions have stayed, while others, which seemed as or more important to him at the time they happened, have gone away. But if the gold-panning similitude is faithful, it means that these memories matter more than the ones that have flown. For gold stays in the pan's center because of its density; it has more matter (whatever that means) in a given extent than anything else.