During the Jurassic period some 180 million years ago, fine mud particles were deposited on the bed of a shallow sea. Over the next millions of years, these formed a layer of claystone up to 150 metres thick – the Opalinus Clay.
The Mont Terri anticline (a large fold) formed some 10 million years ago during the folding of the Jura mountains and was thrust towards the north-west over the Tabular Jura of the Ajoie. In the area where the Rock Laboratory is located, the rock strata dip with an angle of around 45 degrees towards the south-east.