Please
remember the geology of Torbay is special, and all sites are
protected by law.
Causing damage to the Iceland
Spar or using hammers or other tools at this location is against
the law.
This Earthcache is located within The
English Riviera Geopark, which is a UNESCO recognised area of
extreme geological importance.
This Earthcache
has been set up with permission of Torbay Coast and Countryside
Trust http://www.countryside-trust.org.uk/
Further
information on the English Riviera Geopark can be found
at http://www.englishrivierageopark.org.uk/
The Earthcache is accessible all all times, except for at very high
tides.
Parking is
available at Broadsands Beach car park, where there are also
toilets and cafe facilities.
Please be
careful when climbing over the boulders to reach the cache
site
Iceland Spar is a
transparent variety of calcite, or crystallised calcium
carbonate.
Iceland Spar
occurs in readily cleavable crystals, which means that they have a
tendency to split along definate structural planes. Iceland Spar
crystals are remarkable for their double refraction (birefringence). This causes
objects viewed through a clear piece of calcite to appear as a
double image. This property was first described in 1669.
Crystal Cove
includes an exposure of a fault zone, associated with an unusually
wide zone of Iceland Spar, indicating the presence of a major fluid
pathway. The fault zone separates the Brixham Limestone Formation
from sandstones of the Torbay Breccia Formation. This 25m wide zone
of Iceland Spar may be unique in the region.
Torbay has a
varied geological history. Many of the types of rocks in the area
were formed by the laying down or deposition of small pieces of
material or sediment. This sediment was carried in water or by the
wind. When it was deposited it hardened and formed layers of rock,
one on top of another.
The first, and
oldest, group in the area is made up of rocks originally laid down
underneath the sea. They are collectively known as the 'Devonian'
group, and includes slates and limestones. Each of these rock types
were made from a different kind of sediment; slate is mud which has
been turned to stone, whilst limestone is the compressed material
from old coral reefs. These different rock types was laid down
during a separate period and the layers form a sequence in
time.
The second,
younger 'Permian' group also include rocks formed from sediments,
but these were built up on a land surface. At the time of their
formation Torbay was part of a large desert area. Erosion of the
bedrock due to weathering produced a wide range of sediment. The
sandstones that were formed are commonly red in appearance and give
the soil and beaches of the Bay their rich colour today. Unlike the
first group, the different rock types were not formed at different
times. There are two main types; 'Breccia', which was formed by
large, angular fragments held in a mixture of sand, silt and clay,
and 'Conglomerates', which were formed from a similar mixture
carrying rounded fragments.
One very
important difference between the two groups is that the Devonian
rocks, which were formed much earlier than the Permian rocks, were
affected by violent earth movements, which lasted for several
hundred thousand, or even million, years, 300 million years ago.
The original rigid layers of rock were subjected to great forces
from beneath and from the side.
Sometimes this
caused them to bend, or "fold" over, and even to be completely
overturned. On other occasions the pressure merely produced cracks
and fractures, or "faults", within the layers. The rock-mass on one
side of a fault has often been moved, or displaced, relative to the
rock-mass on the other side of the fault. This displacement may
have been caused by one mass being pushed over another, or by the
two masses being pulled apart.
To log your
visit please e-mail us the following information:
1) How high (in
metres) do the visible crystal faults rise above the beach level at
this site?
2) On either
side of the Iceland Spar are two distinct rock types, the Breccia
and the Limestone. Describe the appearance of:
a) Iceland Spar
b) Breccia
c) Limestone
It would also
be great to have a photograph of you with your GPS set in front of
one of the crystal faults (although this is not needed in order to
log your visit)!
This Earthcache is dedicated to my
father, Patrick Puryer (1938-2010) who lived in Torbay. He was a
very keen geologist and chemist, and especially loved the geology
of the Devon coastline.