Silurian Geology in Shropshire

During the Silurian period, around 440 to 400 million years ago, Shropshire was beneath a warm tropical sea.

A world of tropical seas

The seas that covered the Shropshire area around 425 million years ago were warm and shallow, and in the area close to present day Much Wenlock they provided the right conditions for the growth of corals and other animals. Over a period of time these corals built reefs. However these were not huge structures like the modern Great Barrier Reef off the coast of Australia today, but were smaller, perhaps only ten to one hundred metres across and a few metres high.

The remains of these reefs can still be seen today along the top of Wenlock Edge in the limestone rocks that were created by this environment.

Typically these reefs are made up mostly of the remains of corals and creatures called stromatoporoids which were related to modern sponges. They built the majority of the reef, whilst other animals such as trilobites, gastropods, crinoids and brachiopods lived around them and in the gaps between.

Warm shallow seas

As the Silurian period continued the depth of the seas changed many times but in general they were becoming shallower in the Welsh Borders. In the rocks found around Ludlow we have evidence that the seas still supported animals such as trilobites and cephalopods. However, these waters were no longer suitable for the growth of coral reefs.

Further to the south-west of Ludlow, the sea became deeper and underwater channels formed on the edge of the shelf. When sediment cascaded down these sloping channels into the deeper waters it rapidly buried the animals living there.

Now they are preserved in the rocks as perfect fossils, such as the starfish pictured here. Other creatures were preserved as fragments and include impressive animals like Eurypterids, also known as sea scorpions, which probably preyed on smaller animals like trilobites and perhaps starfish.

The end of the Silurian seas

Because the rocks of England and Wales had been moving northwards for millions of years, toward those that make up present day Scotland, the Iapetus Ocean had been shrinking, and by the time the Silurian Period had ended around 408 million years ago it had disappeared altogether.

It was this joining together of the rocks of England and Wales with those of Scotland in the north that caused the Shropshire area to begin to finally emerge from the water onto the southern edge of a new continent. Rivers running off this continent laid down sediment in the remaining shallow water, which in time would also become rock.

It is among some of these last Silurian rocks, around present day Ludlow that we now find the fossilised remains of the first animals to colonise the land and the plants they fed on, as well as some of the earliest fish.