LAGs sub group

CAER CARADOC WALK

7th September 2018

On a fine morning twelve members of the LAGs group set off on a six mile walk from Church Stretton to climb Caer Caradoc for the wonderful views in all directions from the summit at 559m (grid ref SO 4779540)

The route followed the Shropshire Geological Society guide, “An illustrated guide to the wonderful landscapes and geology of the Church Stretton area” by Keith Hotchkiss.

Local geology

Shropshire boasts strata from 10 of the 12 geological periods and just about all can be seen from this walk.

In the late Precambrian, 570-560 million years ago, as the Iapetus ocean closed ( Avalonian orogeny) the area was an extensional marginal basin behind a subduction zone. Volcanoes formed through the thinning crust and the resultant lavas and ashes eventually became the line of Uriconian volcanic hills, Caer Caradoc, Ragleth hill, the Lawleys, and Wrekin. The land between the volcanoes subsided and became marine basins and filled with Precambrian sediments (3500m thick) which eventually became highly folded and appear as the Longmynd syncline seen to the west of Caer Caradoc. The basin margins were formed by the initiation of the Welsh Borderland Fault System which has influenced all the local geology.

The area is therefore highly faulted and folded generally on a SW-NE axis with Church Stretton faults F1 F2 and F3 are included in the walk. The F1 fault is very significant streching as it does from at least South Wales to the Cheshire plain. The fault movement has been both lateral and vertical. Various movements of 50km laterally and 1000m downthrow have been estimated during it’s long active periods ending only 53MA.

During the Cambrian and Ordivician the area was submerged periodically under shallow seas and a sequence of sandstones and limestones is to be found on the eastern slopes of Caer Caradoc and on the walk fossils were found in the small quarry east of the Cwm track. The Ordivician produced the quartzite of the Stiperstones and quartzite is also to be found on the eastern slopes of Caer Caradoc.

Silurian sediments lie on the western slopes of Caer Caradoc where they have been down-faulted along the F1 fault. Most are covered by the glacial deposits on the bottam the Church Stretton Valley.

The walk

From the town centre we crossed the A49 and walked along a field boundary next to a sunken track known as the Cwm track. (At this point in the walk this sunken road seems too deep and narrow to be an ancient worn road so I would think it has been cut by water too)

This approach to Caer Caradoc (SO 467942) is on glacial deposits overlying the Silurian sediments which are not exposed. Ponds to the left are probably the result of glacial activity. The lower slopes of the hill are Precambian Stretton shales then the change of vegetation and slope show the line of the F1 fault with the higher slopes being the Uriconian volcanics of Ragleth Tuff .

Crossing the stream soon after leaving cultivated land there is an intruded Dolerite exposure on the hillside (SO 471943)

Following a diagonal path we crossed pink Rhyolitic tuff exposures (SO 471942) and along the western side of Cwm track is a quarry into the Rhyolite. Looking towards the summit the Ragleth tuff is to the left, Caradoc rhyolite crags of the summit and Wrekin quartzite on the flanks to the right.

The steep climb to the top is rewarded with spectacular views and geology.

The geology is mainly rhyolite with tall flow brecciated crags and exposures arguably showing flow banding. There is andesite on the level surfaces although we didn’t look for it.

The view covers a lot of geological history: to the north, the Lawley (377m) The Wrekin (407m) (Precambrian volcanics), Ordovician ridge and vale (Cardington village) Silurian sediments of the Wenlock limestone ridge and beyond towards Wolverhampton and Dudley. Further round to the south east the Clee hills (Carboniferous) and Precambrian volcanics, Willstone and Hope Bowdler, south to the Ludlow Silurian anticline and west to the Long Mynd Precambrian syncline and finally the far northern view of the Permo-Triassic sandstones of the Shropshire/ Cheshire plains.

A walk of 10 miles to the Clee hills would cross Precambrian, Cambrian, Ordovician, Silurian, Devonian and Carboniferous bedrock - 300 million years,

Descending from the summit the path crosses another fault, the F2 fault at a change of slope and is a step of 100 million years on to the Ordovician strata.

Crossing the Cwn track there is a small quarry with the stone being taken out for farm tracks.This is in the Ordivician sandstones and limestones and fossils were found together with hard conglomerate bands (?)

After this is a relaxing stroll down the track and back to Church Stretton

Alan Hughes 8th Sept 2018

Other references:

Geology of Shropshire - Peter Toghill