Welsh Borderland - Shrewsbury to the Long Mynd
Occupying the northern part of the region, this area extends from Shrewsbury to The Long Mynd and Church Stretton, and includes Telford and Montgomery at its margins. The geology here shows great variation in rock type and age. The landscape around the Long Mynd is characterised by steep sided hills with wide deep valleys at elevations higher than that of the adjacent area. This hill and valley landscape becomes increasingly less pronounced northwards towards Shrewsbury.
The youngest rocks, about 250 million years old, occur around Shrewsbury at the very limit of the region. The Sherwood Sandstone, comprises red-brown sandstones with layers rich in pebbles. It is present in small areas near Shrewsbury and is about 100 m thick. It was deposited after a period of tens of millions of years when the underlying rocks formed a landmass and were being eroded.
Beneath the Sherwood Sandstone and occurring at outcrop more extensively to the east and west of Shrewsbury are older red sandstones that extend to depths of about 200 m below the surface. These sandstones were deposited in an ancient desert approximately 280 million years ago. Beneath this lies about 500 m of reddened rocks known as the Warwickshire Group. In this area these rocks only contain thin coal seams and comprise red-brown to purple-grey mudstone, sandstone and thin layers of limestone. These rocks are present at the surface in central Shrewsbury and to the west and south of the town, where they underlie the younger higher layers in this area and descend to depths of about 1000 m below the surface. Coal Measures, restricted to the area around Telford, formed when vast quantities of sand and mud gradually built up to form large river deltas. When the tops of these deltas were exposed, massive swampy forests grew up and the vegetation from these forests was later buried and compressed to produce layers of coal. These sedimentary bedrock layers rest upon much older basement rocks.
To the east of the Long Mynd lies Wenlock Edge, and the border of the region, and exposes the famous Much Wenlock Limestone. This limestone is about 425 million years old, only extending to depths of about 30 m below the surface at Wenlock Edge and occurring at the surface from Wenlock Edge to near the town of Ludlow. The Long Mynd, and other north-east to south-west trending ridges such as the Stiperstones, and the Wrekin are underlain by very old rocks that were formed over 450 million years ago. These rocks include mudstones, sandstones, limestones and volcanic tuffs — a rock formed from the compaction of erupted volcanic ash. In general, these rocks are particularly hard and this is the reason that the Long Mynd forms such a prominent upland area. The rocks on The Long Mynd are steeply inclined, very thick and are thought to extend to depths greater than 1500 m below the surface. These rocks also host a number of small intrusions of molten magma which occur as sheets cutting through the basement rocks.