According to the first documented entries from 1867, iron was mined at the Ralekesberg. At that time, two test tunnels were dug, one of which is still visible today. Clay and marlstone from the Lower Jurassic period (around 200 million years ago) are found in the cut at the entrance to the pit. On the embankment and in the overburden in front of the tunnel you may be lucky enough to spot the oyster-like shells of the Gryphaea arucata mussel, which indicates that the surrounding rock was formed from marine deposits.