The seasons, like greater tides, ebb and flow across the continents. Spring advances up the United States at the average rate of about fifteen miles a day. It ascends mountainsides at the rate of about a hundred feet a day. It sweeps ahead like a flood of water, racing down the long valleys, creeping up hillsides in a rising tide. Most of us, like the man who lives on the bank of a river and watches the stream flow by, see only one phase of the movement of spring. Each year the season advances toward us out of the south, sweeps around us, goes flooding away to the north.