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Lopolith, igneous intrusion associated with a structural basin, with contacts that are parallel to the bedding of the enclosing rocks. In an ideal example, the enclosing sediments above and below the lopolith dip inward from all sides toward the centre, so that the lopolith is concave upward. Lopoliths, which can be several miles to several hundred miles in diameter, with thicknesses up to several thousand feet, are some of the largest igneous intrusions known. Many large ones are composed dominantly of basic rocks; a classic example is the Bushveld Igneous Complex of South Africa, which is composed of both granite and basic rocks. Many other lopoliths are either composite or differentiated. The feeder of a lopolith is assumed to be relatively small and probably is centrally located; it may connect the lopolith with a larger magma chamber at greater depth. A laccolith also is concordant with country rock, but it is distinguished from a sill by having a flat floor with a domed (mushroom-shaped) roof (see Figure 6). Laccoliths were first described in the Henry Mountains of Utah, where they may measure up to 200 metres thick with basal diameters exceeding three kilometres. Rocks of intermediate silica content generally make up these domed intrusions. In contrast, lopoliths are saucer-shaped bodies with a concave upward roof and floor and are commonly composed of mafic rocks. Lopoliths are huge in size; the Bushveld intrusive complex in South Africa, for example, has an area of about 66,000 square kilometres and an exposed thickness of 8 kilometres. The Muskox intrusion, mentioned above, is another large lopolith, which is estimated to be about 80 kilometres long and 11 kilometres wide (roof rocks covering part of the intrusion prevent an exact measurement). These lopoliths are commonly layered with igneous minerals and rocks; in the Bushveld intrusion, one layer about 1 metre thick consisting of almost pure chromite (an ore of chromium) extends for tens of kilometres.