The Brymbo Fossil Forest

Sites yielding Pennsylvanian (late Carboniferous) coal floras are well known across Europe and North America, but they usually only yield drifted remains of the plants. To understand the ecology of these ancient tropical wetlands properly it is essential that we study in situ remains of the plants. During recent re-development work of a disused steelworks in the Denbigh Coalfield (north Wales) the remains of a stand of mainly arborescent club mosses and horsetails have been discovered, which is providing new insights into how these unusual plants grew. The village of Brymbo, formerly of importance for its industry, lies at the northern extremity of the Denbighshire Coalfield, near Wrexham in North Wales, UK. Coal seams were first worked at an outcrop on the flanks of the deep valley formed along a major fracture in the rocks known as the Bala Fault or the ‘Bala Lineament’. Coal had been mined from at least the year 1410 and mines are recorded as being active in 1540 in ‘Harwd’, the old name for the village. However, Brymbo is best remembered for iron and steel; production of iron, which started in 1796 following the purchase of the 500 acre Brymbo Hall estate by the great pioneering ironmaster, John Wilkinson. In the following years coal output increased dramatically with the sinking of many new shafts. Iron ore and fireclay were also raised; essential raw materials for the new ironworks. With far-sighted proprietors, the works prospered and developed. In 1885 steelmaking began with the introduction of the ‘Basic Open Hearth Process’, the first such plant in Britain. Further process innovations followed, Brymbo latterly specializing in the production of high quality engineering steels until its closure in 1990. Though the modern steelworks was dismantled, many historic structures relating to iron making and coal mining have been retained in a ‘heritage area’, including the original eighteenth century blast furnace and foundry. Recent redevelopment at Brymbo involved opencast mining of coal and burial of the steelworks slag-heap in the resulting void; this created ground suitable for building. The sequence worked in the opencast lay in the upper part of the Middle Coal Measures (Bettisfield) Formation of Duckmantian (‘Westphalian B’) age, within which the most productive seams in the coalfield were found. A small area of exposed Carboniferous rocks near the ‘heritage area’ was saved when an important assemblage of plant fossils was found (Figs 1, 2). Work is still in progress at Brymbo since further site development requires removal of part of the exposure, and so this is not the place to give detailed studies of the flora. Instead, we will give an outline of the type of plant remains that have been discovered so far, including both arborescent lycophyte and calamite stems found in growth position at several horizons, and well preserved compressions of many different kinds of plants. The stands of Calamites stems are the most important feature in the exposure and, as far as we know, the only such Calamites stands preserved anywhere. The exposure is therefore, without doubt, of both national and international importance, and of sufficient value to be included in the UK's network of Geological Conservation Review (GCR) sites and therefore be protected by law as a Site of Special Scientific Interest (SSSI).