200 million years ago, the Jura Sea stretched from the North Sea basin to the far south and covered the old Keuperland. At that time the Hesselberg region was on the edge of this sea. Numerous tributaries brought huge rubble masses from the east of the mainland and formed a multi-layered landscape rich in animals and plants on the sea floor. Over the course of more than 40 million years, the various layers of the Jura rock were deposited one after the other: below that of the Black Jura (Lias), above that of the Brown Jura (Dogger) and as a top level that of the White Jura (Upper Jura or Malm). Each of these strata is characterized by the typical rock and the fossil specimens it contains, as well as its own period. Since some fossils only occur in certain rock layers, one speaks of guide fossils. The guiding fossils in the Jura rock are almost exclusively ammonites. The Jurassic Sea silted up completely in the course of the earth's history. In further millions of years, entire layers of rock were eroded. The protective depression of the Black Jurassic, in which the Hesselberg is located, is the reason why the Hesselberg could not be attacked by wind and water as strongly as the plain between the mountain and the Hahnenkamm. The hard rock was able to withstand and left the Hesselberg as a striking witness mountain, which today protrudes from the landscape like an island. This type of mountain formation is referred to in geology as a reversal of the relief.