Historical geology explores the history of the earth from its origin to the present in general, and the developmental history (evolution) of the living beings in particular. With this historical approach, geology (together with the physics-astronomical cosmology) is an exception within the natural sciences. The latter are primarily concerned with the actual state of their study object and less with its becoming. The formation of the rocks (lithofacies) and the fossils (biofacies) included in them serve as sources of information in geology. The geological history of geological history is based on stratigraphic and geochronological methods.
The basic principle of stratigraphy is a simple principle: the storage rule. A layer in the hanger (‘top’) was later deposited than the layer in the lying (‘down’). However, it should be noted that originally horizontally deposited layers can be displaced or even overturned by later tectonic movements. In this case one is dependent on the existence of clear top-down criteria to determine the original storage. Furthermore, layers which superimpose such displaced rocks with a discordance, ie obliquely angled to the stratification, are also younger than the latter. However, this also applies to magmatic corridors and intrusions from the depths, which penetrate the layers from below.
In the development of a stratigraphic profile, knowledge of paleontology is applied. If the remnants of a particular living being occur only in quite definite layers, but at the same time have a wide, supraregional distribution, and if possible independent of local variations in the deposition conditions, then one speaks of a conducting fossil. All the layers in which these guide fossils are found thus have the same age. Only if there are no fossils, one has to take refuge in lithostratigraphy. Then, the uniformity of certain layers can only be demonstrated with lateral interlocking.
In order to reconstruct tectonic processes, the geologist examines the displacement and the deformation of the rocks by clearing, shaving, disturbance and folding. Here, too, those structures are the most recent ones that strike through the others, but are not themselves displaced. The art here is “intricate easy to see resting moved.” (Hans Cloos)