Looking up at Thorpe Cloud you see a typical
example of hard erosion-resistant limestone formed from an ancient
knoll reef. These sea-floor hills were made of lime mud, probably
generated by micro-organisms. Some grew over 50 metres high, and
they still affect the landscape today after 350 million
years.
Reefs were mostly formed from corals and they became pure white
limestone. Reefs were mostly found in a fringe or barrier around a
lagoon. Another good example of a barrier reef is the hill behind
Castleton on which Peveril Castle was built. Here in Dovedale,
Thorpe Cloud and Parkhouse Hill stand as isolated reefs. Crinoids
grew on the edges of the reefs, so reef limestone is usually
surrounded by limestone containing many crinoid fossils. The
fossilised stems look like nuts and bolts in the rock and are known
locally as Derbyshire screwstone.
Thorpe Cloud as
viewed from the River Dove
Undertake the following via email
:
- Estimate the height of the knoll reef, from the river
valley up to the top of Thorpe Cloud.
- Estimate the diameter of the knoll
reef.
Post the following photograps to your log :
- A photograph of you, and or your GPS, at the SUMMIT of
Thorpe Cloud, where you can see the reef formation at its
best.
- A photograph of the SCREES, which were formed by the
micro-organisms.
Not compulsory, but have a go
:
- Photograph a fossil.
- Photograph some Derbyshire
screwstone.
You may log this earthcache without asking for confirmation, but
you must post photographs on your log, and email the answers to me,
otherwise your log may be deleted.