According to the older theories (originating from the 1930s to 1970s) of Dutch geologists, including Van Bemmelen, compression and extension can and should occur simultaneously at different depths in a mountain belt. In these theories, these different levels are called "Stockwerke". More recent work in geotectonics and geodynamics of the same school of geoscientists (Utrecht and Amsterdam University) by Vlaar, Wortel, and Cloetingh, and their disciples, extended these concepts even further into a temporal realm. They demonstrated that internal and external forces acting upon the mountain belt (e.g., slab pull and intra-plate stress field modulations due to large scale reorganisations of the tectonic plates) result in both longer episodes and shorter phases of general extension and compression acting both upon and inside mountain belts and tectonic arches (See e.g. for extensive reviews, bibliography and discussions on the literature: