Thanks for the comments.
The rocks are Palaeozoic (Carboniferous) dark schist. They outcrop along many km in the southwest coast of Portugal. They build a unique landscape, because of their colour, and because of their strong deformation (they are in places overturned-vertical). The succession of folds is amazing (sorry, I am a geologist after all).
There is also a thin soil cover, made up of cemented sandblown dune deposits. The cement is quite often rich in iron, which gives the cemented dunes a characteristic red-ruddy colour (not seen in these photos).