The Austroalpine nappes are thrusted over the Penninic nappe stack. The massif is almost entirely composed of gneiss from the Siviez-Mischabel nappe. Gairsain is located along an anticlinal thrust plane of the Almora nappe. The zone consists of a nappe stack which is highly metamorphosed. The klippe is the isolated block of the nappe overlying material. The flow over a stepped spillway is classified as either nappe flow or skimming flow. The "root area" is an area where the nappe is completely separated from its substratum. Rocks in the paragneiss of the Monte Rosa Nappe record eclogite-facies metamorphism. Among the Permian rock the Ipoltica Group of the Hronic nappe is best known. Nappe flow regimes occur for small discharges and flat slopes. A nappe whose root area is unknown, is called a "rootless nappe". Sometimes the term "conical surface" is used to mean just one nappe. Several years later, nappe structure was investigated in northwestern Scotland by Charles Lapworth.