Role of gravity in orogenesis

In elastico-viscous materials, the concept of "viscosity" makes model experiments possible, since time appears in its definition as an independent dimension when gravity is the only force acting on the material in both nature and the laboratory. Stitching wax ("shoemaker's pitch") is discussed as a useful material for tectonic experiments. The limit of stress below which solid flow does not take place is very low in this material, permitting slopes of only a few degrees to be maintained. Material raised to greater relative elevations flattens under its own weight, as does ice in an ice cap. Laboratory experiments using stitching wax are described which show that such flattening produces superficial folding in stratified layers of the same material if zones of lower viscosity, such as petrolatum, are present among the layers. Good examples of disharmonious folding are figured.