Geosyncline

A geosyncline (originally called a geosynclinal) is an obsolete geological concept to explain orogens, which was developed in the late 19th and early 20th centuries, before the theory of plate tectonics was envisaged. A geosyncline was described as a giant downward fold in the Earth's crust, with associated upward folds called geanticlines (or geanticlinals), that preceded the climax phase of orogenic deformation.