The massive phyllites of Oisquercq in the Senne Basin are followed up by quartz phyllites which have yielded acritarchs of several different ages for the different localities, viz. Arenig or Llanvirn at Asquempont (Brussels-Charleroi canal section), lower Tremadoc at Virginal (railway cutting north of Virginal Station), Arenig or Lanvirn at Quenast (railway cutting east of Quenast). These new micropalaeontological data show the existence of two quartz phyllitic intervals in the Senne Basin, and suggest the correlation of the first with the " quartzophyllades" of Chévlipont, and the second with the "quartzophyllades" of the Abbey of Villers-la-Ville of the Dyle Basin. They thus provide support for Fourmarier's opinion that the grey, variegated and green rocks of Oisquercq would be the stratigraphie equivalent, in different facies, of the black rocks-of Mousty.