They consist of Mesozoic limestones, shales and marls that were originally deposited on the southern continental margin of the European continent.
In Switzerland, Germany and Austria they are also thrust over the Molasse basin of the Alpine foreland.
Due to this the Helvetic nappes only crop out as a thin band in those countries, which forms the Northern Limestone Alps.
The Helvetic nappes consist of Mesozoic sedimentary rocks deposited on the former southern continental margin of the European plate.
Therefore, the rocks of the Helvetic nappes have a shallower marine facies than the contemporary Bündner slates of the Penninic nappes; and a deeper facies than the rocks of the Infrahelvetic complex of Eastern Switzerland or contemporary sediments in the Jura Mountains north of the Alps.