Fig. 3.

Formation of the three layers of rock alteration in which the engraving is located. Phase 1 refers to the process of alteration by weathering of the exposed lime-dolostone surface (layer 1). The archaeological engraved marks were made on this weathered (soft) surface, which was covered by the Middle Paleolithic sediments of level IV (phase 2). The downward migration of phosphorus and manganese and the upward migration of magnesium and calcium generated two new alteration layers (2 and 3) from the original weathering layer 1 (phase 3). The duricrust layer 3, composed of Mn-rich apatite, protected the original engraving with a black endured coat. Finally, the archaeological excavations at Gorham's Cave exposed this ancient engraved rock surface (phase 4).