The natural, intricately detailed patterns on this limestone were formed in the Jurassic period, about 160 million years ago. Mineral rich water with high concentration of iron and manganese migrated into microscopic cavities between the layers of limestone, creating these stunning patterns, that have been mistaken for fossil sea fans.  Although they look like they were painted on the rock (and have been called picture rocks), this is a completely natural formation. The contrast with the limestone matrix is very strong, and accentuates the sharp details of the dendrites.