Subsidence in the European Area

Extract

The structure of the earth was supposed by Suess to be tripartite, there was an outer layer of rocks mainly granitic, the sal, or sial as it is usually now called. This rested, or “floated”, on a dense layer called the sima, of basaltic character, within which was the earth’s core, or nife, metallic in nature. Such a simple conception has been modified in the light of later knowledge: geologically there is much evidence pointing to the existence of several shells of increasing density within the crust. This is to some extent supported by the evidence of seismology, the layers below the upper sedimentary layer being the Granitic, the Intermediate (of tachylyte or diorite) and Lower Layers (dunite, peridotite, or eclogite) (1). According to the latest information there are four layers intermediate between the granitic and lower layers: the thickness of the sedimentary layer varies from about 2 to 6 kilometres in mountainous regions: the thickness of the granitic layer varies, being about 10 to 12 kilometres in Central Europe. In low-lying regions the total thickness of these two layers is probably about 6 kilometres less than in mountainous regions: “the thicknesses of the other layers are very difficult to determine; the upper two probably have together a thickness of about 15 kilometres, but the others can hardly be determined from the observations” (2).