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| Warmsworth Park in 2007 |
Magnesian limestone
comprises approximately 25% of the solid rocks that underlie Doncaster and,
when I first saw them, I didn't think that they were very interesting - as I
sped past along the M18.
Although there is a distinctive escarpment, as seen when driving north from Hellaby, I could only
see layer upon layer of pale coloured, gently tilted rocks - for a few miles.
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| Variation in colour and texture |
When I examined the Magnesian limestone closely -
in Rotherham and Doncaster - whilst identifying the RIGS, my opinion of these rocks changed.
The dolomitic limestone has been extensively quarried for lime, stone and aggregates and for use in the steel making and glass industries. Many road and railway cuttings, as well as natural exposures, provide opportunities to study the geology of Doncaster in much greater detail.
The dolomitic limestone has been extensively quarried for lime, stone and aggregates and for use in the steel making and glass industries. Many road and railway cuttings, as well as natural exposures, provide opportunities to study the geology of Doncaster in much greater detail.
At Warmsworth Park, a former building stone quarry, there
are extensive exposures of the Sprotbrough Member of the Cadeby Formation,
which is typically a massive, wedge bedded, fine grained and compact limestone,
with virtually no fossils. As an established public park,
it is still regularly maintained and is an ideal field trip site for all levels
of students.
Several safe and accessible quarry faces demonstrate the vertical
and lateral changes in thickness of beds, and there are many examples of
joints and fracturing, often at oblique angles. Stylolites are common and, on
a fresh surface, the stone exhibits a black speckled appearance which, viewed
through a hand lens, is seen to be the manganese bearing mineral pyrolusite,
with its distinctive dendritic pattern of crystal growth.
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| Glacial Till |
Although vegetation inevitably obscures much of the rock,
a closer investigation also reveals sandy glacial till of Quaternary
age, full of angular fragments and sub-rounded pebbles, which provides evidence
of the great changes that have taken place on Earth during the last
300 million years.
In places, the uppermost beds of the limestone are flaggy and highlighted by weathering and the formation of
soil horizons – during very recent geological times.
Also, a particularly
interesting feature is a joint in a quarry face that shows widening
and solution of the limestone by percolating groundwater and is associated with the formation of Karst topography on a once exposed and
weathered surface.
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| A solution feature |
