Query: as continents rise after the overlying ice has melted

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Overdeepening <=SEP=> Overdeepening is a characteristic of basins and valleys eroded by glaciers . An overdeepened valley profile is often eroded to depths which are hundreds of metres below the deepest continuous line ( the thalweg ) along a valley or watercourse . This phenomenon is observed under modern day glaciers , in salt-water fjords and fresh-water lakes remaining after glaciers melt , as well as in tunnel valleys which are partially or totally filled with sediment . When the channel produced by a glacier is filled with debris , the subsurface geomorphic structure is found to be erosionally cut into bedrock and subsequently filled by sediments . These overdeepened cuts into bedrock structures can reach a depth of several hundred metres below the valley floor .   Overdeepened fjords and lakes have significant economic value as harbours and fisheries . Overdeepened basins and valleys filled with sediment ( termed tunnel valleys ) are of particular interest to engineers , petroleum geologists , and hydrologists ; engineers apply the information for developing foundations and tunnel construction , petroleum geologists use tunnel valley locations to identify potential oil fields , while hydrologists apply this knowledge for groundwater resource management .

Plate tectonics <=SEP=> Plate tectonics ( from the Late Latin tectonicus , from the τεκτονικός `` pertaining to building '' ) is a scientific theory describing the large-scale motion of 7 large plates and the movements of a larger number of smaller plates of the Earth 's lithosphere , over the last hundreds of millions of years . The theoretical model builds on the concept of continental drift , an idea developed during the first few decades of the 20th century . The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s .   The lithosphere , which is the rigid outermost shell of a planet ( the crust and upper mantle ) , is broken up into tectonic plates . The Earth 's lithosphere is composed of seven or eight major plates ( depending on how they are defined ) and many minor plates . Where the plates meet , their relative motion determines the type of boundary : convergent , divergent , or transform . Earthquakes , volcanic activity , mountain-building , and oceanic trench formation occur along these plate boundaries . The relative movement of the plates typically ranges from zero to 100 mm annually .   Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere , each topped by its own kind of crust . Along convergent boundaries , subduction carries plates into the mantle ; the material lost is roughly balanced by the formation of new ( oceanic ) crust along divergent margins by seafloor spreading . In this way , the total surface of the lithosphere remains the same . This prediction of plate tectonics is also referred to as the conveyor belt principle . Earlier theories , since disproven , proposed gradual shrinking ( contraction ) or gradual expansion of the globe .   Tectonic plates are able to move because the Earth 's lithosphere has greater mechanical strength than the underlying asthenosphere . Lateral density variations in the mantle result in convection . Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge ( due to variations in topography and density of the crust , which result in differences in gravitational forces ) and drag , with downward suction , at the subduction zones . Another explanation lies in the different forces generated by tidal forces of the Sun and Moon . The relative importance of each of these factors and their relationship to each other is unclear , and still the subject of much debate .

Geology of Scotland <=SEP=> The geology of Scotland is unusually varied for a country of its size , with a large number of differing geological features . There are three main geographical sub-divisions : the Highlands and Islands is a diverse area which lies to the north and west of the Highland Boundary Fault ; the Central Lowlands is a rift valley mainly comprising Paleozoic formations ; and the Southern Uplands , which lie south of the Southern Uplands Fault , are largely composed of Silurian deposits .   The existing bedrock includes very ancient Archean gneiss , metamorphic beds interspersed with granite intrusions created during the Caledonian mountain building period ( the Caledonian orogeny ) , commercially important coal , oil and iron bearing carboniferous deposits and the remains of substantial Paleogene volcanoes . During their formation , tectonic movements created climatic conditions ranging from polar to desert to tropical and a resultant diversity of fossil remains .   Scotland has also had a role to play in many significant discoveries such as plate tectonics and the development of theories about the formation of rocks and was the home of important figures in the development of the science including James Hutton ( the `` father of modern geology '' ) , Hugh Miller and Archibald Geikie . Various locations such as ` Hutton 's Unconformity ' at Siccar Point in Berwickshire and the Moine Thrust in the north west were also important in the development of geological science .

Karoo Supergroup <=SEP=> The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Sahara Desert . The supergroup consists of a sequence of units , mostly of nonmarine origin , deposited between the Late Carboniferous and Early Jurassic , a period of about 120 million years .   In southern Africa , rocks of the Karoo Supergroup cover almost two thirds of the present land surface , including all of Lesotho , almost the whole of Free State , and large parts of the Eastern Cape , Northern Cape , Mpumalanga and KwaZulu-Natal Provinces of South Africa . Karoo supergroup outcrops are also found in Namibia , Swaziland , Zambia , Zimbabwe and Malawi , as well as on other continents that were part of Gondwana . The basins in which it was deposited formed during the formation and breakup of Pangea . The type area of the Karoo Supergroup is the Great Karoo in South Africa , where the most extensive outcrops of the sequence are exposed . Its strata which consist mostly of shales and sandstones , record an almost continuous sequence of marine glacial to terrestrial deposition from the Late Carboniferous to the Early Jurassic . These accumulated in a retroarc foreland basin called the `` main Karoo '' Basin . This basin was formed by the subduction and orogenesis along the southern border of what eventually became Southern Africa , in southern Gondwana . Its sediments attain a maximum cumulative thickness of 12 km , with the overlying basaltic lavas ( the Drakensberg Group ) at least 1.4 km thick .   Fossils include plants ( both macro-fossils and pollen ) , rare insects and fish , common and diverse tetrapods ( mostly therapsid reptiles , temnospondyl amphibians , and in the upper strata dinosaurs ) , and ichnofossils . Their biostratigraphy has been used as the international standard for global correlation of Permian to Jurassic nonmarine strata .