[1] The massif consists of early Paleozoic (late Cambrian and Ordovician in age) metamorphic rocks, mostly quartzites and phyllites.
In other parts of the Ardennes they form a basement which is covered by only slightly metamorphosed late Paleozoic limestones and sandstones, that only saw a low degree of metamorphism.
On the other hand, the early Paleozoic rocks were deformed and metamorphosed to a higher degree during the Caledonian orogeny (about 450 million years ago).
Both the Caledonian basement and the low grade cover rocks were deformed again during the Hercynian orogeny (about 350-280 million years ago).
In the core of this anticline a number of massifs of early Paleozoic rocks crop out.