The characteristics of a region’s soils are largely controlled
by two factors: climate and geology. Soils are mostly composed
of broken-down minerals from the bedrock (along with,
critically, organic matter), and the weathering process is
driven by climatic conditions. Soils can also form within the
sediments deposited in an area, however, as is the case in the
flood plains of river valleys. And there are other things that
can transport sediment to a new home—like wind. This is what
makes the soil of the island of Bermuda so interesting. It seems
like they don’t belong. The island’s shallow bedrock is composed
of gray limestone, mainly in the form of broken-up bits of
skeletons from marine organisms—the same stuff that makes up the
beach sand. The soil, however, is rusty-red and clay-rich. The
reason for this sharp contrast has long been debated, with two
hypotheses gaining the most support. One possibility is that the
limestone contains a fair amount of clay, which is left behind
as the limestone dissolves.