Welsh Journals

LIMESTONE PAVEMENTS IN WALES S. D. WARD and D. F. EVANS Limestone outcrops in Wales are extremely localized and the- limestone pavements which occur on them are a little known phenomenon. The Carboniferous limestone on which they are formed outcrops in both North and South Wales, where the pavements which occur on the north crop of the South Wales coalfield, between Black Mountain in the west and the area around Ystradfellte in the east, are amongst the southernmost in Britain. In North Wales the limestone outcrops in Anglesey and the Great Orme, and then sweeps southwards in an arc through Denbigh and Ruthin; another arc lying to the east runs from Prestatyn to south of Llangollen. Small exposures of pavement occur along both these outcrops. Limestone pavements are bare expanses of limestone deeply indented by fissures and grooves. Those of Wales are of very limited extent, whereas in the North of England, around Morecambe Bay and in the Yorkshire Dales National Park. they can be very extensive. Pavement formation dates back to the last Ice Age, when the erosive action of passing ice sheets moulded the surface of the rock. Limestone solution since that time has modelled the surface features. The two basic elements of a pavement surface are described by Yorkshire dialect words, which have been adopted in scientific literature. The network of fissures formed by solution along natural cracks in the rock are known as grikes, and the intervening limestone blocks as 1. Lily-of-the-valley (Convallaria majalis) growing in the crevices of a flaky limestone pavement in South Wales.