Field trip to Stepaside Ironworks and Pendine 30/06/18

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    We gathered at Stepaside Ironworks [SN141074] at 10.30 am on the last day of flaming June  with shorts and sunhats at the ready. Our first task was to identify the building stones used in this magnificent Victorian edifice. The orange brown colour of the stonework reflected the iron rich Coal Measure sandstone and some blocks glinted in the sunlight where quartz crystals had developed within joints in the sandstone; muscovite mica flakes could also be recognised on some surfaces. When we reached the wall of the casting house there was ample evidence of iron smelting in remnants of slag where we discovered fragments of ironstone, anthracite and limestone.
    This site of industrial archaeology reflects the importance of economic geology in the 19th century in South Pembrokeshire. All the materials for iron making were available locally; anthracite, iron ore and limestone, and the Saundersfoot Railway had already been extended to Stepaside when the ironworks opened in 1849. However, supplies of bedded iron ore from the coalfield were limited and as economic conditions declined, the ironworks was forced to close in 1874. Today the ruined buildings have been restored and developed as a tourist attraction.
    The stone casting house with its three arched doorways and circular openings stands as a monument to solid Victorian engineering. The two blast furnaces originally stood in front of the furnace wall, one to each pair of arches. The furnaces were loaded by overhead bridges leading from the upper platform where the raw materials were assembled. Before the furnaces were charged, the anthracite was converted into coke in the coke ovens and the iron ore was roasted in the calcining kilns. Compressed air to aid combustion was provided by the blowing house, which is the tall building to the right of the furnace wall.

    After exploring the ironworks, we climbed up the pathway to the remains of Grove colliery. This mine was opened in 1853 to supply anthracite from the Kilgetty Vein. A branch line from the Saundersfoot railway linked the colliery to the ironworks. Today you can still see the ruins of the winding engine house that lifted the cages up and down the shaft, and the Cornish pumping house that contained a 274 hp beam engine that raised water from the mine

    From Stepaside we drove across to Pendine for lunch; this seaside resort  was crowded with holiday makers and those attending the motor rally on Pendine Sands. However, we managed to leave the crowds behind as we traversed westwards from Dolwen Point [SN234079] to examine the Carboniferous limestone succession that forms the northern boundary of the Pembrokeshire and South Wales coalfields. The base of the limestone is seen at Dolwen Point and the strata dips south west for about 1 km to Gilman Point where the top of the succession is exposed. At Dolwen Point the Avon Group (Lower Limestone shales) is composed of well bedded and jointed grey limestones in the centre of which is a thick bed of calcareous mudstone. The mud has undergone soft sediment deformation induced by gravity on a gently inclined depositional slope. There are slump folds, convolute beds, pillow beds and fractured blocks that have sunk into the mud; the mudstones are sandwiched between more competent limestone beds.
    The Abercriban Oolite overlies the Avon Group near the cliff steps just west of Dolwen Point. This is a massively bedded bioclastic limestone where we examined fallen blocks containing shell beds and lenses with productid brachiopods (Dictyoclostus), single corals (Zaphrentis) and colonial corals (Lithostrotion junceum).  We then made our way across the sands to Gilman Point where the massively bedded Dowlais Limestone is exposed. On the western side of the headland the limestone is overlain by cemented periglacial head deposits up to 10 metres thick containing large clasts of quartzite and limestone. This material appears to have slipped down the side of a preglacial valley having been lubricated by surface meltwater as the frozen ground began to thaw at the end of the Devensian glaciation in a process known as solifluxion. On returning along the beach we discovered some remains of a submerged forest. The submergence relates to the Flandrian marine transgression at the end of Pleistocene times.
    John Downes

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