The Swabian Jura is made up of strata from the Lower, Middle and Upper Jurassic periods. Taken together, these rock strata are roughly 700 metres deep.
They were created between 190 and 130 million years ago at the bed of the Jurassic Sea and were elevated later. Holzmaden lies at the foot of the Swabian Jura in the middle of the Lower Jurassic.
Its oily shale is what remains of the putrid mud which was deposited on the bed of the Jurassic Sea. It is here that we find particularly large numbers of excellently preserved fossils, for the cadavers of dead animals decomposed only very slowly in the anoxic mud.