This figure is taken from Otto Ampferer's "Über die Gleitformung der
Glarner Alpen" published in 1934 in Sitzungsberichte der Akademie der
Wissenschaften in Wien, Mathem.-naturw. Klasse, Abteilung I, 143. Band, 3.
und 4. Heft.
According to Ampferer the Helvetic nappes were emplaced by gravity gliding
on the already eroded Infrahelvetic foreland. According to him the Glarus
thrust followed an erosional surface ("Reliefüberschiebung"). This
surface was intensely flattened by the overthrusting of the nappes.