As all rock climbers will know, the outcropping gritstone of The Roaches is fantastic "grippy" stuff to climb on. It is fractured and eroded into cracked faces, grooves and huge boulders the size of small bungalows. I've often wondered how the weird and evocative rock shapes along the edge here were formed - so here goes with a geology lesson, courtesy of good old Wiki;
Roaches Grit is a coarse sandstone which outcrops widely throughout the western part of the Peak District of northern England and gives rise to several significant landscape features in the area. Its counterpart in the eastern part of the National Park is the Ashover Grit.
The combined Roaches Grit and Ashover Grit are amongst the most widespread sandstone units within the Millstone Grit Group of the Peak District. Along with other similar sandstones, such as the immediately overlying Chatsworth Grit, it is assigned to the Marsdenian sub-stage of the Namurian stage within the Carboniferous period around 317 million years ago.
The two units which, prior to the doming and erosion of the central Peak District were once one, are interpreted as delta-top sandstones. The deposited material was brought down from a northerly source by braided rivers.
So, put simply, around 317 million years ago, a range of mountains were pushed up to the north and an immense Amazon or Mississippi sized river spread it's delta over much of what is now England (and Holland and Belgium). As the delta built itself closer, sand and grit covered the shale and limestone layers. This was a dynamic environment with tides and strong currents which often moved and re-sorted the sand banks and bars of the delta; these layers ("units of deposition") can often be seen in exposures such as the Roaches or Stanage Edge.
Most notably, up along the Roaches Ridge is an outcrop displaying a splendid example of "Crossbedding", where there exist bedding planes which seem to contradict each other - the main sedimentary layer in one plane, but interspersed with apparently randomly angled beds too.
I've looked at several explanations of this phenomena and I'm still not convinced I understand it - but it's good to know that we have such a prime example here on our doorstep!!