the karoo supergroup was formed in vast inland basin starting 320 million years ago, at a time when the part of gondwana which would eventually become africa lay over the south pole. icebergs that had calved off the glaciers and ice sheets to the north deposited a 1-km-thick layer of mud containing dropstones of varying origins and sizes into this basin. this became the dwyka group consisting primarily of tillite, the lowermost layer of the karoo supergroup. as gondwana drifted northwards, the basin turned into an inland sea with extensive swampy deltas along its northern shores. the peat in these swamps eventually turned into large deposits of coal which are mined in kwazulu-natal and on the highveld. this 3-km-thick layer is known as the ecca group, which is overlain by the 5.6-km-thick beaufort group, laid down on a vast plain with mississippi-like rivers depositing mud from an immense range of mountains to the south. ancient reptiles and amphibians prospered in the wet forests, and their remains have made the karoo famous amongst palaeontologists. the first of these karoo fossils was discovered in 1838 by scots-born andrew geddes bain at a road cutting near fort beaufort. he sent his specimens to the british museum, where fellow scotsman robert broom recognised the karoo fossils' mammal-like characteristics in 1897.