Geoscience Reference
In-Depth Information
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The Northampton Sand (labelled N on Figs 151 and 168)
In the northeast of Area 9, the Northampton Sand at the base of the Middle Jurassic
is important not only as a hard material that resisted erosion during the creation of the
present landscape, but also because it has been quarried widely as an economically im-
portant source of iron.
(4)
The Middle Jurassic oolitic limestones (labelled O on Figs 151 and 168
)
The Middle Jurassic of this Area was one of the earliest successions anywhere in the
world to be analysed in detail and traced from place to place. This pioneering work was
carried out by William Smith, as described in the treatment of Area 8. He divided this
limestone-dominated, fossil-rich part of the Jurassic succession into two major subdi-
visions, the Inferior Oolite (lower and older) and the Great Oolite (higher and young-
er), and was able to trace and map them over many tens of kilometres, although the two
divisions together are normally no more than 100 m thick. Although these Middle Jur-
assic sediments also include mudstones, sandstones and ironstones, a wide variety of
limestones is present which dominate the local landscapes, forming the Cotswold Hills,
one of the main scenic features of Southern England. Most of these layers of sediment
were deposited in the shallow tropical seas that covered Southern England during the
Middle Jurassic. The variation in the sediment layers reflects changes in the environ-
ments of sedimentation, including periodic invasions of muddy material brought in by
rivers. Much of the limestone is honey-coloured, and its wide use as a building stone
is one of the most attractive features of the villages and towns of the Cotswolds (Fig.
172).
