Pembrokeshire’s coastal landscape
The rocks along the coast rise in an almost unbroken series from the 1.5m year old pre-cambrian base up to the coal measures dating from 300m years ago. Erosion has worn away more recent deposits.These were then massively distorted by two huge mountain-building distrubances and fragmented some sections exposing rocks such as igneious, volcanic, sandstones, shales, limestones, conglomerates, slates and quarzites – making this county a geologists’ delight. Here can be found every degree of hardness and acidity.
400 million years ago the Caledonian movement tilted and imposed a SW-NE grain of landscapes across the northern areas of Pembrokeshire.Later hercynian shifts impacted onthis area again and created a WNW-ESE trend whereby the southern areas of old Red Sandstone was folded, and pressed the carboniferous rocks against the northern bloc.
In terms of soils in Pembrokeshire the coverage is mostly acid glacial clays, sands and gravels while the whole county is dominated by a level platform cut by the action of the sea 17 m years ago at which time the sea level was 200 feet higher. In the south most were planed off making a flat top but in the north remnants of the ancient volcanic and igneous survived. this left what is called Monadnocks which stand above the land e.g. St Davids head all along the coast up to Strumble Head – once these were islands in an ancient sea.When sea levels fell new streams found the easiest ways through the Caledonian faults and folds, initially cutting deepley gauging glacial valleys such as at Solva, Gwaun and Nevern. Some lower courses were drowned like at Haverfordwest, Porthclais, Ritec and Bosherton. The pre-glacial course of the Cleddau became Milford Haven‘s deep water channel. The whole coast is deeply indented.
Wind and salt
The climate is the key to the profusion of wild flowers along the coast path – even in February the temperature is usually at least 6c and the coast if frost-free thanks to the warmth of the Gulf Stream. Over 50 plants are in flower even on New Years Day and the rain fall is about 32″ per year. For each mile inland there is an extra inch of rainfuall.There is also the highest amount of sunshine for the whole of Wales.Sounds great, but that is not considering the wind factor. Each year there will be about 32 days of force 8 winds or above pa mostly between october and february. Sea spray affects all plants on the exposed coast – with winds of up to 100 mph – called halophytes from the greek for sea-salt. The plants are internally adapted to cope with variations in the salt, comparatively fleshy, perennial with often woody rootstocks.
Cliff-edge dessication – few plants can survive along dry cliff edges in gravel – have hairs to hold onto moisture – small or varnished leaves with roots that can probe deep into cracks.