The South Pembrokeshire coast continues its spectacular scenic way as you travel eastwards from Manorbier to the middle cove known as Church Doors at Skrinkle Haven. The intervening mile or two sees a transition from the older red Devonian rock to younger grey Carboniferous limestone higher in the geological succession. Looking down on the bay you can see that it is divided into three parts by two seaward projecting ridges of rock known as Church Doors and Horseback.
The rocks around the bay are now stacked in remarkable vertical layers after earth movements have altered their position from the original horizontal strata. To the right of the steep metal staircase as you descend to the beach, Avon Group Limestones, formerly known as the Lower Limestone Shales, are made from thousands of very fine layers alternating with narrow hard bands that underlie the pebbles and boulders of the shore, and are exposed in the cliffs and a narrow promontory. These strata are collectively referred to as the Church Doors Limestone.
A small natural tunnel, accessible only at very low tides, passes through the promontory from the middle cove to the west cove of Skrinkle Haven. At the moment that tunnel seems to be the only way of getting to Skrinkle Haven proper but it use is not recommended. It is only open and available for a very short time and it is easy to get stuck on the other side with no way up the cliff as the tide rises. Also, the seabed level on the far side is a lot lower that the Church Door side and water rises comparatively much faster than in the middle cove making it additionally dangerous.
The staircase down to the beach marks the point at which the Avon Group limestones are replaced by Pembroke Group limestones. Behind and to the left of the steps as you reach the beach, there is a transitional zone marked by an increase in the proportion of limestone and chert beds. The limestone is faulted and has many white calcite veins. The promontory known as the Horseback is composed of Black Rock Limestone and has an incredible natural arch where blocks of stone have fallen. It is interesting to note the texture of the barnacle encrusted rock at the waterline with its marked pitting caused by bioerosion.
Allaby, M. 2008, Oxford Dictionary of Earth Sciences, Oxford University Press, 3rd Edition, 978-0-19-921194-4.
George, G. T. 2008, The Geology of South Wales: A Field Guide, firstname.lastname@example.org, 978-0-9559371-0-1, pp 22 and 137-141.
Howells, M. F. 2007, Wales, British Regional Geology, British Geological Survey, Nottingham, Natural Environment Research Council, 978-085272584-9, pp 112-120.