Mm to cm thin bentonite layers in the Schlieren Flysch represent volcanic ash layers.

The geochemical composition of the layers suggests basic to acidic volcanism and a with-in plate derivation.

The ash layers predate known Alpine magmatic and volcanic activities.

The ash layers show well coherence with ash layers found in the Austrian Alps and in the Danish Basin.

The ashes originate most probably from the British Tertiary Volcanic Province related to the opening of the North Atlantic.