Forestry Commission statements: This is a working wood/forest, and you may come across work sites, workers and vehicles during your visits. Please avoid all working areas and obey any safety signs and instructions. You must not enter any areas where access has been restricted.
In the interests of safety the Forestry Commission strongly recommends that persons visiting the EarthCache carry a mobile phone and first aid kit and leave details of the mobile number, route and expected return time with a friend, relative or responsible person.
As with all walks in the Forest of Dean, you may encounter wild boar so please familiarise yourself with the guidelines before setting off. Click to see Guidelines.
The cache is placed with kind permission of the Forestry Commission.
The Suck Stone is reputed to be the largest detached block of rock in the British Isles and this huge boulder of conglomerate Old Red Sandstone and Quartz weighs in excess of 30,000 tons.
Conglomerate is a clastic sedimentary rock that contains large (greater than two millimeters in diameter) rounded clasts (pebbles). The space between the clasts is generally filled with smaller particles and/or a chemical cement that binds the rock together.
Conglomerate can have a variety of compositions. As a clastic sedimentary rock, it can contain clasts of any rock material or weathering product that is washed downstream or down current. The rounded clasts of conglomerate can be mineral particles such as quartz, or they can be sedimentary, metamorphic, or igneous rock fragments. The matrix that binds the large clasts together can be a mixture of sand, mud, and chemical cement which sets to form the rock.
Conglomerate forms where sediments of rounded clasts at least two millimeters in diameter accumulate. It takes a strong water current to transport and shape particles this large so the environment of deposition might be along a swiftly flowing stream or a beach with strong waves. There must also be a source of large-size sediment particles somewhere up current. The rounded shape of the clasts reveals that they were tumbled by running water or moving waves before being engulfed by the sediment.
Conglomerates often begin by being deposited as a sediment consisting mainly of pebble and cobble-size clasts. The finer-size sand and clay, which fill the spaces between the larger clasts, is often deposited later on top of the large clasts and then sifts down between them to fill the interstitial spaces. The deposition of a chemical cement then binds the sediment into a rock.
If during the deposition of sediment a change in current speed or sediment grain size occurs or perhaps the sediment supply is cut off, a bedding plane forms. Bedding planes are surfaces that separate one stratum from another. Bedding planes can also form when the upper part of a sediment layer is eroded away before the next episode of deposition. Strata separated by a bedding plane may have different grain sizes, grain compositions, or colours.
To claim this EarthCache, complete the following tasks which can be completed by referring to the text above and email your answers to me via the email link or the Message Centre on my profile page:
At waypoint 1 (N 51° 49.380 W 002° 39.946) observe the general appearance of the rock.
1) Describe the colours that you can see in the rock.
2) Estimate the size of the smallest and largest clasts visible from where you are standing
3) Does anything about the appearance of the embedded rock fragments lead you to conclude that they were, or were not, tumbled in water?
Now move round to the back of the stone (waypoint 2 - N 51 49.381 W 002 39.939))
4) How does the appearance of this face differ to the previous one?
5) This huge block fell from Near Harkening Rock which you can see up the slope through the trees. Why do you think there is such a contrast between the two faces of the Suck Stone? (Hint: One of the faces would have formed the top surface of the cliff)
Photos of you or your GPS near the stone would be great.
You don't need to wait for my reply before writing your log but please note that logs will be deleted if I don't receive the answers via the email link or the Message Centre on my profile page in a reasonable time. All submissions will be acknowledged.