A Scandinavian indicator stone is a glacial erratic composed of a characteristic rock type derived from a small known source area in Scandinavia. This term not only applies to igneous and metamorphic rocks but also to some sedimentary rocks. The Jotnian Sandstone and most of the Palaeozoic limestones, and the Old Red Sandstone are not included in the definition, although the presence of these and other rocks provide some evidence about the source area(s) of erratics and should certainly not be neglected in a stone count. In all cases we recommend including the whole assemblage of erratics/stones in such account. This makes it possible to use several methods of Interpretation. However, it should be pointed out that the practise used in the past, whereby each researcher had her/his own method of interpreting stone counts, has proved to be unsatisfactory. We demonstrate on the bases of over 2000 counts of indicator stones that we have carried out on assemblages mostly from Lower Saxony and Schleswig-Holstein, but also from other N.German states and neighbouring countries, that the TGZ method (LÜTTIG 1958) yields the most reliable results. In addition to this method, the sources of individual indicator stones may be plotted on a so-called circle map and can be integrated with possible source data and the relative frequencies of other erratics in the assemblage. Some rock types are more suitable as indicator stones then others. It is unwise to use clearly unsuitable rock types; this would considerably reduce the reliability of the method and lead to erroneous results.

Weathering is a continous process by which rocks are broken down and decomposed by the action of humidity (rain), wind, temperature changes, chemical agents, bacteria and plants. Being an integral part of the rocks cycle, weathering is the initial stage towards denudation, which results in general lowering of the land surface. An essential feature is that it affects rocks in situ; no transportation is involved. This is the factor which dsitinguishes weathering from erosion. The two main types of weathering are mechanical and chemical. Climate plays a leading role in weathering, whereas chemical weathering is almost absent in arid regions. Effecrtive freeze-thaw cycles are confined to cold temperate and permafrost climates.

Erosion is part of the process of denudation which involves the wearing away of land surface by mechanical action of transported debris. Main cycles of erosion are glaciers, wind erosion, marine erosion.

The Petrified Forest is primarily a geological park, which owes its origin to the climate and geological events. He is part of the so-called Painted Desert and shows with its various layers a strange and impressive scenery. Characterized by erosion, it is a treasure trove of fossils. The rock formations show a chronicle of the past and give clues about the events of bygone days. In the park you can exposure rock strata until 234 million years ago. The colorful desert hills, the flat mesas and shaped hills attributable primarily to Chinle Formation and are fluvial sediments, caused by water movement. Countless fossilized wood and tree trunks bear witness to a scrumptious earlier fauna.

Emerged as a product of erosion from water, frost and wind which has shaped the spectacular pillars (hoodoos) the Bryce Canyon National Park is one of the most spectacular natural amphitheater. The eroded Claron limestone in which also fossils are found, leaves the impression of a subtle army from limestone warriors. Named after the Mormon Pioneer Ebenezer Bryce, the natural spectacle was 1928 declared as national park.

One of Madagascar's geological specialties are the so-called Tsingy: bizarre, at first sight hostile Karst landscapes, though form, due to the inaccessibility, a refugial area for some species. The word Tsingy means "walking one tip-toes" or "where one cannot walk bare-foot" in Malagasy language, an accurate description for the partially razor-sharp rock formations which can reach 20 m in height and with ends which can be as thin as pencils.

Best known and most impressive are the Tsingy of Bemaraha in the West of the island and the Tsingy of Ankarana in the North, both widespread Karst areas. In the North, as well, about 10 km south of the city of Antsiranana, one can find the Red Tsingy which have been washed out of the lateritic layer of earth.