The subsoil is made up of fresh water molasses comprising of an alternation between soft layers and rocky banks (sedimentary rocks transported by glaciers in Mont-Pèlerin, called “poudingue” locally, and sandstone in Cornalle), on which the Rhone Glacier left rubble as it receded.
The deposit of sedimentary layers of molasses that nowadays form the rocky outcrops which characterise the Lavaux landscape
The formation of The Alps which would shift and deform the layers of molasses
The big freezes which would carve the valley known as the Lemanic basin
The rocky base of Lavaux consists of molasses (sedimentary rocks formed at the head of the Alpine mountain range as it formed). The molasses settled during the Tertiary Era between 34 and 7 million years BC. In Lavaux, only the fresh water molasses surface. The salt water molasses settled at deeper levels.
The fresh water molasses are particularly rich in fossils which are mainly preserved in the layers of soft rocks such as shale and coal. Plant fossils, vertebrates (crocodiles and turtles) and invertebrates (snails and lake mussels) were discovered. In the middle of the 19th Century thousands of plant specimens (145 species of which 75 were new to Switzerland and 44 new to science as a whole) were found on a site in Moulin-Monod.
Except for the Tertiary Era molasses, other geological formations appeared in Lavaux in the Quaternary Era (from 1.75 million years BC until current time). Only the deposits from the last Ice Age (The « Würm », 100,000 – 15,000 BC) are still present as the last glacier swept away almost every deposit from the ancient freezes.
Source : BOREL, Gilles, MARCHANT, Robin, « Géologie », in Lavaux, Vignoble en terrasses face au lac et aux Alpes, Lavaux World Heritage Site Application File for UNESCO, Cully, January 2006, p. 44.