Black Rocks is a gritstone outcrop on the hillside above Cromford on the way to Wirksworth, near Bolehill. It is popular with climbers & affords spectacular views of the Matlock Gorge & Derwent Valley Mills World Heritage Site. It is a designated Country Park, with parking, toilets, a picnic area & cafe (weekends & high season only). It can also be reached via the High Peak Trail, which runs alongside the bottom of the site. Alternative parking (£1 for a half day - honesty box), is available at the National Stone Centre, which the High Peak Trail also passes, allowing you to park there & take the short walk or ride along to Black Rocks & beyond.
Black Rocks has been created over thousands of years through weathering. Weathering is the breakdown of rocks at the Earth's surface & is different from erosion. The basic difference is that erosion involves particles being worn away & moved elsewhere, whereas weathering always happens in situ.
There are three types of weathering; physical, chemical & biological. Rarely do these types act in isolation; rather they combine to act together in some way.
Examples of physical weathering include the cycle of freezing & thawing of rainwater in cracks, causing them to expand & eventually break the rock apart. Physical weathering is particularly likely where there is little soil & no plants grow.
Chemical weathering occurs when rainwater reacts with mineral grains in rocks to create new minerals & soluble salts. This happens particularly when the water is slightly acidic & occurs more quickly at warmer temperatures.
Living organisms contribute in many ways to weathering. The roots of plants, particularly trees, often grow through cracks in the rock & as the roots expand, they prize the rock apart. Algae & lichens break down the rock surface to obtain nutrients using chemical secretions & even some animals bore into rocks.
To claim this Earthcache, you will need to visit the site to find out some information as well as carrying out some simple research online. There is no container to be found here. You must message or email us your answers to the questions below. Logs which are not accompanied by answers in a timely manner will be deleted.
Please note that you will need to climb onto the rocks & approach a sheer drop to answer one of the questions. You can either clamber directly over the rocks (no specialist climbing equipment is necessary to do this) or if you circle around & approach from above you can walk straight onto the top of the rocks. Please take care when visiting as surfaces are uneven, can be slippery & there are sheer drops. Only attempt this if you feel confident enough to do so. Children should be supervised at all times.
1) The gritstone at Black Rocks is named after a Derbyshire village. What is the name given to this variety of gritstone?
2) Having read about weathering above, describe which type(s) you believe shaped Black Rocks over the millennia. Explain why you have reached this conclusion, giving examples where appropriate.
3) At the given coordinates, you will find a large D-shaped indentation or pothole in the surface of the rock, that is normally filled with rainwater except in periods of extended dry weather. Please measure it & tell us what the maximum width of this weathered pothole is.
Photographs of Black Rocks (not the pothole) or the views, with or without you in them, are most welcome, but are not a logging requirement.
We hope you enjoy your visit to Black Rocks & have fun exploring.
We are grateful to the Forestry Commission for their kind permission to allow us to publish this cache. Please note that rocks or fossils should not be removed from the site.
Sadly, there was a recent spate of highly offensive graffiti at Black Rocks, which delayed publication of this Earthcache. Whilst the worst of this has now been removed, please be aware that this is an ongoing problem at the site & remain vigilant, especially if visiting with children.
Congratulations to Alfreton Divers for FTF!