Silurian

During the Silurian period, what was to become Wales was still located south of the Equator. The Silurian lasted from 440 to 400 million years ago.

More land emerged from the sea in this period. Land plants developed and, towards the end of the Silurian, animals were found on land. In the rivers freshwater fish became abundant.

In Pembrokeshire, Silurian igneous rocks are only found in a small area around Marloes and also form the Island of Skomer. The rocks on Skomer are typically basalt, rhyolite and dolerite. A band of Silurian sedimentary rocks stretches from Haverfordwest to Narberth. These were formed in the shallor seas and rock types include mudstones, sandstones and conglomerates. The mudstones contain classic examples of fossil brachiopaods, trilobites and corals. An important section of Silurian sedimentary rocks are exposed at Haverfordwest and protected as a Site of Special Scientific Interest (SSSI). At Marloes the whole sequence of Silurian rocks is spectacularly exposed in the cliff section.

In May, Bluebells carpet the Island of Skomer, and Thrift and other specialist plants are also found in abundance. The island is a National Nature Reserve and home to many seabirds and supports a number of Puffine colonies. Unique to the island is the Skomer vole, a subspecies of its mainland cousin. Larger, different in colour and less timid than voles elsewhere, it is thought to have developed on the island from mainland stock that arrived with settlers during the Iron Age.