Visit of SWGA 28th April 2017

South Wales Geological Association visited Martley for a second visit on 28th April.  We met at the Memorial hall, the coincidental charity coffee morning supplying excellent refreshments as the group perused our pop up geology display.  Here is my report of the day that I very much enjoyed escorting around features near Horsham and in the Teme Valley:

An enjoyable and slightly daringly adventurous field trip with South Wales Geological Association, on occasion breaking a few of the rules of the risk assessment, but as experienced adults we considered ourselves capable of making the necessary on the spot decisions in that regard. A little bit of a scramble now and then is good for the soul. Steve Howe, SWGA, genial, knowledgeable leader, only lost one man (found wandering, by others, in Martley at lunchtime), some explaining to do over the border back in West Wales.  No matter. First the Permian, south of the Berrow.  Reached by a stiff climb, the arete of Haffield Breccia, the whole height of the Berrow here, gives a wonderful vantage point over the Teme valley around Knightwick and Whitbourne. A small pit perplexed our experts and in turn their questions flummoxed me:—How do we know it IS Permian? How deep is the bed here? From which mountains do the clasts come? How come there are large rounded clasts abutting and within beds of smaller angled pieces and gravels? What formations are represented here?  Questions notes, answers needed, more exploratory work to be done. The fact of coal measures higher up on the hill also furrowed brows and set the tone for a moderately challenging day both intellectually and at times physically.

Travelling on to Brockhill Court by kind permission of Sir Anthony Winnington to inspect the igneous dyke of putative Carboniferous age, and its heated intrusion, around 300Ma, into the rather moist country rock of Raglan Mudstone.  Averting our eyes, for later enjoyment, from the feature walls flanking the gateway to the parking area, we wandered down the drive to the hidden, unsuspected yet spectacular road stone quarry that is Brockhill Dyke.  Baked country rock with its voids, filled later with zeolites and calcites, crystalline magmatic dyke material and aphanitic (very fine crystals) chilled margin samples, lay in wait for our inspection and speculation.  Intrepid Steve, followed by others, two steps forward, at least one back, up the loose soil slope to the higher faces in order to more closely inspect contact points and spherical weathering.  This latter is sure evidence of the crystalline dyke material.  At the surface the rock takes in moisture that oxidises iron, expanding it, causing shells to break away from the blocks.  Half way up the slope we estimated the width of the magmatic material at around 6-7m.

Back to the cars and the walls—plenty to look at there—collected lunch and up to the lone pine above the dyke where we enjoyed wide ranging views of the valley whilst dining on the delights we had each packed. We wondered how far the dyke extended and whether the BGS geology map is correct (it seems to be not too far out), what all the minor hills and bumps in the valley consist of, whether the dyke shielded land from further erosion and so on.  We fought our way through thick saplings to the top of the quarry and most descended the badger path down the lip of the quarry to the road, wondering if the Lord of the Rings beech contorted tree roots that we used as hand rails en-route, were really an entrance to other worlds.

Into the cars, over New Mill Bridge and further up river so we could find our way to unmatched Southstone Rock, among the largest tufa deposits to be found in England.  One of my ‘Prepare to be Amazed’ moments when out of the trees a giant tufa cliff emerges, complete with rushing water fall, passageways and ferns all set amid primeval woodland   Another of these places is when you round the corner of the shed into Ian’s quarry garden.

At the ‘rock’, the spring gushing from the hillside in its grotto, perhaps a remnant of a once sacred site where on stood a church and later a cottage (see a picture in Cliff Barnard’s Book ‘A Tale of Two Villages’), the top of the waterfall with its giant coppiced yew, (is this another sign of a sacred site) and the precipitous view down valley from tufa cliffs.  Most of the huge deposit seems to have formed around a particular moss that likes the limey, alkaline waters and for its appetite becomes petrified.  In turn though, there are good examples of drip tufa where carbonate saturated water has run down over the mossy substrate and formed laminates of a more solid, less vesicular material. Finally to view an outcropping of an important, but not the only, source of the lime, a continuous covering of Bishops Frome that drapes the Silurian Raglan mudstone and underlies Lower Devonian deposits of St Maughans formation.  This is a calcareous sandstone often in a marly matrix, much used where it occurs, for building. The Bishops Frome is a calcrete, a type of chemical soil formed in this case, in a dry climate where occasional, slightly acidic rain seeps quickly down, takes some of the carbonate out and is later drawn to the surface by capillary action. There are other ways in which calcrete forms.  In the Teme valley where it underlies many square miles of the Bromyard Plateau, it is layer up to a few metres thick, sitting on top of the impervious Raglan Mudstone, giving rise to a line of springs.

Lastly we drove to Shelsley Walsh church, one example of a building made from local tufa, though possibly not from Southstone, rather from now hidden quarries above the church alongside the famous Shelsley Walsh hill climb.  A site worth visiting whatever your interest is, a magical and ancient place of worship in a quiet spot (except on race days of course).

Thanks for your second visit SWGA, your interest in our area and the questions you raised.

Ref HERE from Murchison

HERE for some very interesting references in a book from the late 19th century, copied by Google.  Conjectures about flow rates, the original course of the stream as well as passages and caves in the rock, now collapsed.  Also the thousands of tons of tufa taken away from the site.

HERE from disappointingly, a climbing blog, reference to the church that used to be on top. Personally having done some climbing, I am appalled that ‘rock climbers’; should even think about this as a climbing venue given the fragility rock and the damage that could be caused.