The exposed basal rocks of present-day Bermuda
are highly altered carbonate eolianite of the Walsingham
Formation, which, although not precisely dated,
have reversed magnetic polarity—probably the
Brunhes/Matuyama boundary dated at 780,000 yr
ago (Hearty and Vacher, 1994) and, thus, is correlated
with the early Pleistocene. A massive red soil (the Big
Red Soil, or BRS) developed on the Walsingham
during an extended period of lower sea level (900–450
thousand yr ago; MIS 23–12) during which no
carbonates were deposited on the platform, as even
during highstands sea level was well below the
present datum. Most of the Bermuda platform is
exposed when sea level drops to the 210 m bathymetric
contour. No vertebrate fossils are known from
this first half or more of Bermuda’s subaerial history