Derwent Tors #3 - The Cakes of Bread
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A series of 3 Earthcaches on a walk taking you high above the Derwent Valley with breathtaking views where you will see some unusual rock features, these caches will explain what these odd boulders are and how they came to be....
High up above Derwent and Ladybower, something strange is going on......... an unusual collection of strangley shaped objects scattered around the landscape, standing tall seemingly impervious to the rigours of the Dark Peak weather, but are they impervious? and what exactly are they ?
Derwent Edge is a Millstone grit escarpment that lies above the Upper Derwent Valley in the Peak District National Park, The millstone grit forms the edge of the high peat moorland plateau on the eastern side of the valley above Ladybower Reservoir, the edges being the last remains of the gritstone which originally covered all of the Peak District, what you see now, these small exposed sections, would at one time have been everywhere, but not in the peculiar shapes they are in today, most of the millstone grit was scraped off by glaciers in the last ice age, it is actually called Gritstone but known as 'millstone grit' (as it was THE choice for making coarse millstones) it is a sedimentary rock composed of coarse sand grains with inclusions of small stones. It is a coarser version of sandstone. It was laid down in the late (upper) Paleozoic era, in the Carboniferous period, in delta conditions, The area here is well known for it's unusual gritstone 'Tors' which is what these 3 caches will show you, A 'tor' is a rock outcrop formed by weathering over a very long period of time, usually found on or near the summit of a hill, as these are.
The Cakes of Bread
The Cakes of Bread are named unsurprisingly as that is exactly what they appears to be, bread cackes in Derbyshire terms! as you approach it from afar, it is a small outcrop than The Wheel stones, but I think it is far more striking, again formed by erosion, the locals have named these rocks and the names have stuck that well that they are actually shown on the OS maps ! From here if you have come from the previous 2 caches why not carry on up to Back Tor, yet another Tor millstone outcrop with a Trig point and simply amazing views !
Gritsone, formation, its' uses and geology
Alternating layers of sand, mud and grit became compressed to form a huge 'sandwich' across the area now known as the Peak District, this can be seen notably in the outcrop at Mam Tor. These sediments became the shales, siltstones and sandstones (MILLSTONE GRIT) of the Dark Peak. The presence of turbidites in these layers indicates the growing instability of the delta sediments followed by repeated subterranean landslides out into deeper water. This instability continues into the present as the thin layers are very loose and friable. When water seeps between them, catastrophic landslips result such as Mam Tor(another Earthcache)
As gritstone is a sedimentary rock it frequently shows signs of cross-bedding or current bedding. It is quarried for building material. as previously mentioned British gritstone in the past was used to make coarse millstones, which at the time were used to mill flour, grind wood into pulp for paper and it was also manufactured into grindstones to sharpen metal blades.
The rock is much loved by English climbers, among whom it has almost cult status and is often referred to as "God's own rock". The rough surface provides outstanding friction, enabling climbers to stand on or grip the subtlest of features in the rock and as a result Derwent Edge is very popular with rock climbers - Why not have a climb up them while you're here ? you will see why they like it when you touch this rock for the first time
The Ice Age and the part it played in forming this area
As the glaciers moved over the Peak District the majority of the rock surface was scraped away and what is left today is smaller and some larger groups of millstone grit sections that have been formed by the actions of wind, rain and frost over many centuries, many of which now looking like animals, objects and even people ! you may be able to see something different everytime you see the stones from a different angle.
As the great rivers brought succeeding coarse and fine material down to the delta over the ages, it formed layers of what became harder and softer rock. The layers can clearly be seen here, almost like stacks of pancakes ! A consequence of this is that the Grit weathers unevenly along its planes and joints as you can see in the rock formations here on Derwent Edge, take a look at how rounded the rocks are in places and how the age they are from has created them.
Please bear in mind when doing these caches that the area is a serious walk and proper boots will be needed, it can get very boggy up here, proper sturdy footwear and outdoor gear is essential
IN ORDER TO CLAIM THIS EARTHCACHE PLEASE COMPLETE THE FOLLOWING TASKS:
1. Please post a photo of yourself or your GPS with the Cakes of Bread in the background
2. Please tell me how many 'Bread Cakes' there are here and your estimate of how high they are at the highest point (email me - not in your logs please)
3. Please post photos of the layering of the 'cakes' where erosion is clearly evident, ie noticeably thinner sections
4. Roughly what angle do the 'cakes' sit at to the ground ? (again email me - not in your logs please)
PLEASE NOTE: I receive a very high number of Earthcache emails, I can’t reply to them all otherwise I’d be doing nothing else all day, as has always been the case there is no need to await a reply from me regarding your answers…. However due to numerous people thinking they can just log these caches without emailing any answers, and/or completing the required tasks these will be picked up, and the logs will be deleted without further communication. To facilitate this Please email your information either before, or AT THE SAME TIME OF LOGGING THE CACHE, Thanks.
I hope you have great fun discovering the area!
(No hints available.)