This period is so named because many of the limestones entering into the
composition of the formations it comprises, consist almost entirely of
an aggregation of rounded concretionary grains resembling, in outward
appearance, the roe or eggs of fishes, and each of which contains a
nucleus of sand, around which concentric layers of calcareous matter
have accumulated; whence the name, from ωον, _egg_, and λιθος, _stone_.
The Oolite series is usually subdivided into three sections, the
_Lower_, _Middle_, and _Upper Oolite_. These rocks form in England a
band some thirty miles broad, ranging across the country from Yorkshire,
in the north-east, to Dorset, in the south-west, but with a great
diversity of mineral character, which has led to a further subdivision
of the series, founded on the existence of particular strata in the
central and south-western counties:--