Geology trip to The Chevin, Otley 27 Mar 24

Five members of the Geology group met at East Quarry Car Park on the edge of Otley and headed East along the path following the Geology Trail.  We made good use of the Chevin Forest Park Geology Trail leaflet to guide us and to try and make sense of the geology around us.  The quarry excavated Addingham Edge Grit which formed in the Carboniferous period. Our first stop was to look at the tidal laminations in the sandstone.  Each laminate was formed in a single tide and is an extremely rare sight.

Further along the path, we headed up a steep and slippery slope to see cross-bedding in the Addingham Edge Grit.  This stone is very course and were formed from sands deposited in a river delta.  As well as the horizontal bedding planes, we could also make out other lines which sloped down at a gentle angle representing sandbanks in the river channel – this is known as cross-bedding.  We also made out rusty red colour on the rocks which comes from iron.

Further along the path, we turned south to climb steeply up the hill side before turning along a path which took us past the Vacca Wall, a man-made wall of standing blocks of local sandstone used to keep cattle from straying.

After a lot of mud, we made it to the top of the Great Dibb Landslip.  We were standing on the top of Long Ridge Sandstone and looking down a steep slope into Otley formed by landslips.  At the end of the ice age, the slope became unstable in summer when the ice melted and the sandstone slipped on the mudstones below. Today, the trees help to stabilise the slopes.

Our route continued through lots of mud and then climbed up to another set of crags made of Doubler Stones Sandstone which lies on top of the mudstones.  We could make out evidence of slump bedding with lots of contorted lines.  On one of the rocks, we found fossils of tree branches caused by trees and branches being washed downstream by floods.

Further along, the Doubler Stones Sandstone showed really clear evidence of cross-bedding.  Sand grains rolling along the river bed would have fallen down the slope of sandbanks and settled at an angle.

We climbed up above the crags to a wall where we had a welcome rest looking south to Guisley and Menston.  From there, we headed in the disused Yorkgate quarry with its pond and up to an outcrop of Doubler Stones Sandstone sloping 24 degrees to the South.  This sandstone was made up of much smaller sandgrains than the other stones we had been seeing and was dimpled with the fossils of tree routes.  Just above the outcrop, we could see a thin layer of coal from the Morton Banks coal seam encased in grey fireclay.

From there we splashed through yet more mud and standing water across to the Variscan Orogeny. This was caused by a plate collision at the end of the Carboniferous period and which led the uplifting of northern England into the Pennine anticline.

Finally, we walked along the ridge to Surprise View where we were able to make out the towns and cities of the Aire Valley to the south and east as well as Brimham Rocks to the north and over to Upper Ribblesdale and Upper Wharfedale.  It was starting to rain a little at this point, and was quite windy and exposed on the ridge, so we headed back down the face of the escarpment back to the car park.

Leader: Jane Welsh

Words and Photos: Jane Welsh

Content created by Keith Parker