This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This is also a horticultural and agricultural operation. Its object is to crush the clods still further, to make the surface more level, and to compress the particles sufficiently to hold moisture and make a firm root run. It would be fatal to growth to have large fissures in the soil, or to have it so loose and spongy that tiny seeds would sink down so deeply that the seedlings would never be able to reach the light. Rolling ground, or treading on it with the feet, therefore, has the effect of packing the soil particles together, without making them adhere so closely as to prevent the entrance of air and water.