Definition: Flysch

It is a siliceous-clayey sedimentary soil, sometimes carbonated, of terrigenous, marine or lacustrine detrital origin, composed of a powerful succession of rhythmic alternations of turbidities - an elementary sequence of a few decimetres to a few metres in thickness, which was deposited by a turbulent current, resulting in grain sorting phenomena producing, individually, from the base to the top, a sandstone-conglomerate bank, topped by a silty bank, then a very clayey and schistose pelitic bank.