Abereiddy is the best and easiest place in the UK to find graptolites. It is also an outstanding place where you can see and photograph in situ graptolites, crammed into the sloping bedrocks. Although this site is a SSSI (so hammering the bedrock is strictly prohibited), there is no reason why you would want to disturb the bedrock. The foreshore is full of rocks that can be picked up without tools and contain better specimens than those in the bedrock.
♦ Drive to Abereiddy bay, where there are plenty of parking spaces at the bottom of the hill. From here, you can either search the beach, cliffs and foreshore or follow the narrow cliff top path to the disused quarry. However, the quarry is fenced off and, by far the best place to search is the foreshore, to the left of the bay.♦ Ref: 51.93590°N, 5.20546°W
FIND FREQUENCY: ♦♦♦♦♦ – Graptolites from Abereiddy Bay are very common and easy to find. In fact, if you look carefully, they can even be found in the shale that forms the car park. Entire bedding plains of these fossils are seen to the left hand side of the bay, with sea-rounded shale pebbles also rich in graptolites
CHILDREN: ♦♦♦♦♦ – This is an excellent location for children, where they can safety search the foreshore pebbles for fossils. It is a lovely part-sandy bay, with toilets and often mobile food vans. And, very little walking is required to get to the site.
ACCESS: ♦♦♦♦♦ – Abereiddy Bay is very easy to find. Fossils can be collected immediately from the car park and from around the bay (especially to the left).
TYPE: – The best place at Abereiddy Bay to collect fossils is from the loose foreshore rocks. Fossils can be seen in (but not collected from) the cliffs and could potentially be collected from the cliff top quarry, although this is now fenced off for health and safety reasons.
The land is owned by the National Trust and is part of the Pembrokeshire Coast National Park. It is a SSSI, so hammering the bedrock (including the cliffs) is strictly prohibited. However, since the cliffs are mostly unfossiliferous volcanic rocks, fossil collectors will want to find the Ordovician shales wedged in between the cliffs. Fortunately, chunks of shale regularly get worked out of the cliffs and onto the beach. Therefore, all you need to do is to walk down onto the beach and look at the soft, flaky shales found there, using a hammer only when larger pieces need to be split.
Apart from graptolites, other fossils have been reported from Abereiddy, but, other than trace fossils, these are not common. Among the rarer fossils recorded are planktonic trilobites called agnostids and, at certain horizons, brachiopods of the type usually referred to as Lingula, although they are almost certainly not closely related to the Lingula alive today.
The graptolite that is normally found at Abereiddy Bay is a species known as the ‘tuning-fork’ graptolite, Didymograptus murchisoni. It existed for only a relatively short period of time, during the later part of the Middle Ordovician, about 470 to 464mya. Therefore, it is used as an index fossil for this period of time, which geologists refer to as the Llanvirn stage (after a farmer’s cottage on the lane leading to Abereiddy).
Abereiddy is a tiny place, but the bay has become a popular tourist attraction because of a flooded quarry known as the Blue Lagoon. Quarrying for slate ended in 1901 and the sea eventually broke through into the quarry, creating what is, in effect, a small natural harbour. In fact, for a while, fishermen used the quarry for precisely that purpose, but nowadays, it is maintained purely for recreation, with a nice little beach at one end and diving points at the other. Compared to the strong currents that hit Abereiddy Bay, the water within the Blue Lagoon is very calm, which adds to its popularity with families.
The rocks in the cliffs on either side of the bay are mostly volcanic and metamorphic, which is of course what attracted the quarrymen looking for slate. However, Ordovician shales are wedged in between the cliffs and chunks of this shale regularly get worked out of the cliffs and onto the beach.
The high ground on the south side of the bay is formed by steeply dipping murchisoni shales from the Upper Llanvirn, where Didymograptus murchisoni is quite common, along with Glyptograpthus sp. To the north, the succession passes up into beds of Llandeilo age, which makes the main foreshore (continuing north) the Castell Limestone, formed by alternating beds of Caradocian limestone and shale. A narrow cliff top path crosses north over the northern headland, leading to a small cove eroded in up-faulted Didymograptus bifidus beds, from the lower Llanvirn. This is a fault and the disused Porth Gain Slate Quarry provides excellent exposures of these.
Common sense when collecting at all locations should always be used and prior knowledge of tide times is essential. Tides on this part of the coast can be very dangerous, so make sure you return before the tide turns. The sloping shale cliffs easily crumble, so keep well away from the base of the cliff at all times. The shale can also be quite sharp, especially freshly fallen loose material.
You do not need any tools to collect from Abereiddy Bay – just take something to wrap your fossils in and some bags. The graptolites are well preserved in the sea-rounded shale pebbles and loose shale, which has fallen at the bottom of the sloping cliffs towards the left hand side of the bay. Rocks do not need to be split to find fossils, but, if you do need to split larger rocks, a hammer is useful.
This site is an SSSI. This Special Site of Scientific Interest, means you can visit the site, but hammering the bedrock is not permitted.