The key to the new hypothesis is a thin layer of black soil found at more than 50 North American sites. (discovermagazine.com)
In addition there were areas with rich black soil good for growing celery, lettuce, cabbage, and carrots. (bombmagazine.org)
Poor soils are the rule on the Coastal Plain, though rare exceptions have formed some of America's most famous agricultural regions — for example, the citrus country of central Florida's limestone uplands and the Cotton Belt of the Old South, once centred on the alluvial plain of the Mississippi and belts of chalky black soils of eastern Texas, Alabama, and Mississippi. (britannica.com)