Hills covered in schist used for building houses and making roof slates. Present in the towns of Pluherlin, Malansac and Rochefort-en-Terre, slate quarries were used from the 13th to early 20th century. There is a great deal of slate located in the village of Rochefort-en-Terre. Today, Les Grées is considered a protected area. You will find Saint Michel Chapel at the end of Place Saint Michel.