A migmatite is a heterogeneous ultrametamorphic rock, which has both igneous and metamorphic rock properties. It is formed as a result of partial melting (called anataxis), which occurs when an existing rock is subjected to high pressure and temperature conditions. Its occurrence in this area of the Natural Monument of the Alcantilado de Montedor marks the contact between the Plutonite of Bouça de Frade and the embedded metasedimentary rock that testifies the metamorphic conditions attributed to the second phase of Varisque deformation.