There was a chunk of time in my childhood — maybe as long as two years — where every kid at school was completely focused on marbles. Having first persuaded our parents to buy us each a large bag of them, the school yard was daily transformed into a huge marble tournament. I can't remember all the specifics of the games (dropsies rings a bell), but the overall sense of building a collection is still vivid. Every game in which you bested your opponent, you got to keep his or her marble. You save…