Geo trail qr code archway 2

Geo Trail

Known for its grand collection of historic buildings, this is only part of the story of Royal William Yard. To find out more, we need to travel back some 380 million years!

This area has an incredible history - and you can see for yourself when you take a walk around. Take a stroll along the Geo Trail to uncover the ancient past and geology of the area.

Take a stroll along the Geo Trail, winding around Royal William Yard and along the South West Coast Path at Devil’s Point to uncover more about the past, and the amazing 380 million years of geological history that can be discovered here!

To get involved, collect one of the Geo Trail leaflets from the visitor office at the entrance to Royal William Yard and scan the QR codes you discover. Alternatively, you can view all of the videos here.

University of Plymouth image close up corals in Plymouth limestone on the Brewhouse building 2

What to look for around Royal William Yard

Our Geo Trail will guide you around some of the fascinating fossils and sensational stone in RoyalWilliam Yard, but there are many more that you can spot for yourself. Keep an eye out for white shapes, blobs and outlines in the stone–once you spot a few and know what to look for, you will notice them all over the Yard!

  • The warm shallow seas of the Devonian period left their mark on the local limestone and if you look closely, you can see bivalves (shells with two hinged halves like a cockle), several species of hard coral, ridged shells, and stromatoporoid sponges.
  • Tiny microfossils known as conodonts (tooth like elements from a small extinct, but enigmatic, eel like creature) and ostracods (small shelled crustaceans) can determine the age of the limestones. They have been found at Devil’s Point, and they date this limestone to 382 million years old.
  • It’s not just microfossils that we can find; the limestone here was once a coral reef bound by corals and stromatoporoids, with crinoids (sea lillies) and brachiopods also living in this environment. The species of coral found here are indicative of a tropical environment, telling us a little about the warm, barmy waters that Plymouth once had, a very different environment to today!
Rwy archway tunnel firestone

Our very own volcanos

Drake's Island is a Plymouth landmark, but not many people realise it is actually made in part, of Basalt, which is formed from lava! This is an igneous rock, made through lava cooling and solidifying, and its presence indicates that significant volcanic activity was taking place in Plymouth during the Devonian period.

The volcanic rocks we find on Drake’s Island are not just basalt though, they are made up of rocks known as ‘tuff’ which is a volcanic deposit of the ash and tephra that is ejected from a volcano. Containing course and fine grained of pumice and lava with gas bubbles filled with calcite, and pieces of hyaloclastite (fragmented lava containing volcanic glass) we can determine that these volcanoes erupted underwater, and on to our shallow coral reefs.

We can date this volcanic activity as occurring between 390 and 385 million years ago, at the same time as the coral and stromatoporoid reefs were flourishing! In fact it may be due to earlier volcanism over a significant period of time that the Plymouth limestone reefs could form! Scientific studies suggest that the Plymouth limestone lies on volcanic rocks up to 300m thick. The eruption of these extensive lavas formed elevated areas, providing the perfect shallow water environment on which the Plymouth limestone reefs could form.

7 super close up of coral in Plymouth limestone Clarence building

Discovering Devil’s Point

At parts of Devil’s Point, especially as you get closer to the sea, you can spy the dark, jagged natural rock. This is the original bedrock, Plymouth limestone, the same limestone that we can see used in the buildings at Royal William Yard.

The limestone here at Devil’s Point and that you can see outcropping over at Cremyll and all the way along the Hoe and across to Mount Batten has been researched extensively. The plants and flowers also tell us about the geology that lies beneath them. The limestone creates alkali soils perfect conditions for some of the plants we see here – it has more than 80 varieties of wild flowers.

Samphire grows there, although you have to be quick, as the young leaves in early Spring are the edible ones! Another tasty plant is Alexanders, which the Romans used as an alternative to celery. You can also spot Buck’s Horn Plantain, Field Eryngo, Tree Mallow and Rock Spurrey – look for the sign along the South West Coast path with pictures to help you spy them.

Geo Trail videos

If you are unable to use the QR codes around the yard, you can explore our geo trail videos here.