Geological journey to the tropics

Members of the East Lothian Antiquarian and Field Naturalists’ Society attended a field trip on the 9th July to look at the geological interest along the coast between Whitesands and Barns Ness near Dunbar.  This was led by geologist Fiona McGibbon following her successful talk to the Society in January.  

We were shown the extensive areas of limestone on the beach which were at different levels and ages.  These dated from the Carboniferous period over 320 million years ago and most was formed as coral in tropical seas when Scotland was near the equator due to Continental Drift – it has since moved a long way north.  Changes in sea level caused by several ice ages over a very long time scale account for the different nature of the limestone layers.  The nearby limekiln was a reminder of more recent commercial use when the limestone was burnt with coal to create lime for spreading on farmland.

One of the most remarkable and striking features on one area of limestone are numerous circular bowls in the rock about a metre across which look most unnatural but were in fact created by ancient Lycopod forests.  Lycopods were like huge mangroves and their roots ate into the rock to create these striking “root bowls”.  

It became apparent that much of the limestone was full of fossils of marine creatures from long ago.  Some were very noticeable as in the “Dunbar Marble” which is not a marble but was once used as a decorative building material.  Others required very close examination of the rock on hands on knees when you could just discern fossils of burrows and sponges.

We looked at a prominent fault line running down into the sea and walked along a raised beach left behind as a result of sea level changes since the last ice age – caused by a combination of the melting ice and the land rising once released from the enormous weight of ice.  

A lot of geology was packed into a very enjoyable and fascinating two hour walk in the sunshine.  We are very grateful to Fiona for sharing some of her knowledge and for explaining complex subjects so clearly.  I doubt we shall ever look in the same way again at rocks on the beach !  

John Hunt July 2022

By eastlothianantiquarians

The East Lothian Antiquarian and Field Naturalists’ Society, established in 1924, is a membership organisation and a charity. Member events include outings and a copy of the Transactions for just £15/annum. We also welcome short contributions from members for the website.