The Cheviot massif lying at the centre of the range is an outcrop of Early Devonian (360 million years ago) rock lying to the north of the Iapetus suture. This suture marks the closure of an ancient ocean as the continent of Avalonia was subducted under Laurentia. Cheviot Central granites are the remnant of an ancient volcano surrounded by an arc of andesitic lava flows, tuffs and agglomerates of the Cheviot Volcanic Formation. The Cheviot summit marks the highest point at 815m shown as the stretched feature on the horizon in the photo below. Yeavering Bell from where the photo was taken lies over Andesite bedrock.
The bedrock is scarcely visible since it has been eroded and smoothed in layers of glacial till into rounded green hills. The tills are a mix of sandy diamictons till, morainic and solifluction deposits, sand, gravel, silt and clay originating from the Cheviot Hills. The deposits contain clasts derived predominantly from volcanic and intrusive rocks (basalt, andesite and granite) of the Cheviot Hills.
The twin peaked Yeavering bell pictured below is classed as a mountain although an easy climb. Wooded at the more sheltered base, as the ground rises Bracken predominates then moorland summits steep enough to form bare scree. Scree forms as a result of freeze- thaw processes on the rock.
Andesite is the name used for a family of fine-grained, extrusive igneous rocks that are usually greyish in colour. They often weather to various shades of purplish brown. It is rich in plagioclase feldspar minerals and may contain biotite, pyroxenes, or amphiboles.
The scattered rocks below have a pinkish glow where the surface is fresher.
This larger boulder is pinkish orange due to the presence of orthoclase feldspar.
A close up of a specimen shown the fine grained material with larger white phenocrysts probably of plagioclase feldspar. A phenocryst is a conspicuous, large crystal embedded in a finer-grained matrix of smaller crystals in an igneous rock.
This boulder like many in the uplands is covered in Lichen. The green is ‘Map Lichen’ (Rhizocarpon geographicum) forming a complicated pattern with the grey Rhizocarpon reductum.
Lecanora sulphurea, the dull green crustose is often parasitic on Aspicilia
Calcarea pictured below.
The bright yellow crust looks like Candelariella coralliza.
This sample of Cladonia rangiformis was lying loose at the summit but I could not identify where it came from but it could easily occur up here.
Lichens : Frank S. Dobson