ABSTRACT
This chapter will first provide some historical aspects and geometric data to illustrate the concept of unconformity, which is essentially the foundation of modern geological science. When it has regional value, an unconformity separates an older basement, which has often been repeatedly deformed and eroded, from a sedimentary cover that has undergone little tectonic deformation. It may also indicate the end of a continental crust thinning process. Since geology is rooted in landscapes, these concepts will be illustrated by regional examples. Subsequently, two models of unconformities to be 3D printed will be presented to illustrate the concept for educational purposes.
