Well, Alluvial deposits must have been the leftovers then. My yard has perhaps an inch of topsoil and then 20-40 feet of terrible, horrible clay. That's why pine trees seem to flourish down here. Their roots can penetrate that clay. The flooding of our rivers, year after year, decade after decade, century after century has deposited the great, Alluvial soil, and that's why our Delta region has such great farmland. Now that flooding is controlled to a great extent, and no more deposits will be had. Though we are 300 miles north of the coast, lots of seashells are found up here, so eons ago, we were covered by a great ocean.
