Dave B

Dave B

Posted on 11/05/2015


Photo taken on November  2, 2015



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Keywords

Rock
Geography
Geology
Staffordshire
The Roaches
Peak District National Park
The Pennines
Wind erosion


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Wind erosion on Roaches rock face

Wind erosion on Roaches rock face
One for geographers (well, geologists, at least.) These rock faces tell two different stories. One is of their formation well over three hundred million years ago. The British Geological Survey tells that this is "Roaches Grit - Sandstone. Sedimentary Bedrock formed approximately 314 to 315 million years ago in the Carboniferous Period. These rocks were formed from rivers depositing mainly sand and gravel detrital material in channels to form river terrace deposits, with fine silt and clay from overbank floods forming floodplain alluvium, and some bogs depositing peat; includes estuarine and coastal plain deposits mapped as alluvium." It is so easy to see the numerous layers. Even on this rock face above the heather there are at least 5 or 6 major layers with 4 intermediate ones between. But I wonder why the main layers seem to have been tipped up when the intermediate ones are mainly horizontal? The rocks at Hartland Quay all seem to have been bent and twisted after they were originally formed but what has happened here? One presumes sedimentary rocks to have been formed horizontally or at least in line with river flow but why are they inter-spaced with layers obviously different? Level, then tipped, then tipped back level for a bit, then tipped again, etc. does not seem likely. Someone will be able to add their pennyworth I hope. I would truly love to hear an explanation.

The other story is what has happened in the 300 million years since their formation. Were they formed at about this level (about 1600 feet above sea level) or have they been lifted since then? And isn't it fascinating the way the wind erosion, using its own loose grit particles, has picked at the weaker layers and so exposed the formation for us all to see.

Ewald has particularly liked this photo


Comments
Ewald
Ewald
Schön erklärt und toll Präsentiert!*
3 years ago.
Dave B has replied to Ewald
Danke.
3 years ago.