The geology of Northamptonshire consists largely of sedimentary
strata laid down during the Jurassic period (195 to 145 million
years ago). During this period, the current Nene valley formed a
narrow channel between the high grounds of the southern Pennines
and the north-western shore of the Anglo-Belgian land mass. Rivers
from the uplands carried sand and shells which were deposited near
the coast in the slower moving waters. Over time the sediments were
compacted and cemented together with calcite, silica or limonite to
form the limestones, sandstones and ironstones that today form the
"Northampton Sand Formation".
These rocks have been quarried for hundreds of years, and a few
buildings (such as the Church of the Holy Sepulchre in Sheep
Street) still remain from the 12th century. Many of the original
pits are long gone, but there are still some working quarries - for
example at Pitsford, Harlestone and Pury End.
The coordinates for this cache take you to the site of the
former New Duston Quarry, which dates from as far back as the
sixteenth century, and maybe much longer. Much of this quarry has
now been infilled, and it has been incorporated into a housing
estate; but the exposed face is still visible in a number of
places. A thick layer of dark brown ironstone can be clearly seen
at the base, above which lies a 1.2m layer of sandy limestone (also
known as "Pendle"). The upper layer of more yellow sandstone is
unfortunately less clear due to downwash from the soil above.
Unusually, this quarry also produced Duston "slates". This is
not true slate, but calcerous sandy rock that happens to split
suitably along bedding planes - thus producing good quality roofing
material.
To log this cache, please email your answers to the following
questions via my profile:
- Approach the rock face closest to the given coordinates. Which
is the harder of the two layers of rock - the upper limestone
layer, or the sandstone beneath? Describe at least one feature
which supports your answer.
- What evidence can you see to show that this stone might be
useful for slate roofing?
- Photos are optional - but it would be good to see a photo of
you at the quarry, or maybe a picture of a stone building from your
local village?
Many thanks to Northants Borough Council for their permission
and support for this Earthcache (the first in
Northamptonshire!)