Similar to the radiolarites, the aptych layers are not completely rounded, because they are very hard. Their place of origin was far from the mainland in the deep sea, therefore they have a high silica content.
In the upper Jurassic period (146 to 112 million years ago) also aptychs were deposited beside radiolarians and hair stars. Aptychs are two-part, calcareous mandibular apparatuses of ammonites (= extinct subgroup of exclusively marine cephalopods) with which they could close their shells. The rock is called aptych layers because of these valves.
Like the peaks of main dolomite, weathered stein limestone and radiolarite, the peaks of aptych layers are very rugged and majestic.