28 NORTH AMERICA/Continental Interior Figure Glacial debris (A) Glacial outwash deposit, which covers extensive areas of the Continental Interior; (B) glacial gumbo till deposited directly from the glacier; (C) large glacial erratic in Lawrence, Kansas; (D) thick loess deposit (glacial wind blown dust) in central Nebraska position Drainage south of the southern extent of the glaciers was profoundly affected with overloads of water and material, and this latest episode of history is evidenced by the underfit streams, stream piracy, and extensive stream and river terrace development The final adjustments are taking place today as the Continental Interior returns to ‘normal’ The Sediments The succession of stratigraphic units on the craton could be and have been described as monotonous, but they are anything but boring Special features of these unique sedimentary units are their; (i) lateral persistence; (ii) extreme thinness, the tremendous ratio of width to thickness; (iii) sharpness of boundaries; and (iv) cyclic nature The contained micro- and macro-fauna and flora (or lack thereof) in these sediments not only gives information on conditions under which the sediments formed, but provides information on relative age for correlation from one area to another, where the sediments are not continuous Understanding life as it occurred in ancient times is based mainly on understanding the occurrence and distribution of similar forms today In addition to the usual sedimentary types, such as sandstone, siltstone, shale, limestone, dolomite, anhydrite, and gypsum, that occur in the Phanerozic sequence, there are four rock types that are formed under special circumstances: chalk, salt, black shale, and coal Chalk is made up of tiny micro-organisms that accumulated in the open sea in warm water (Figure 9A and B) Major chalk deposits throughout the Earth are prominent in the Cretaceous (Zuni) and the Kansas chalk is famous for its marine vertebrate fauna Salt is formed when and where marine waters are restricted and evaporate (Figure 9C) Salt is used here as an all-inclusive term for minerals precipated from the evaporation of sea-water The Silurian (Tippecanoe) and Permian (Absaroka) are two of those times in Earth history when vast areas of salt were formed on the craton under these conditions The black shale accumulates under confined conditions at the bottom of the sea, where because of lack of water circulation and reducing conditions, all forms of carbonate and other soluble material are dissolved (Figure 9D) Radioactive material is concentrated in the black shales, making them distinctive subsurface marker beds on gamma-ray wireline logs and easy to correlate On the North American craton, black shales are prevalent in the Late Devonian to Early Mississippian (Kaskaskia) and numerous thin but persistent ones in the Middle and Upper Pennsylvanian and Lower Permian (Absaroka) Lignite and coal form near sea-level and are thus a good palaeoenvironment indicator (Figure 10A and B) In the Interior Province, several basins contain bituminous coal, mostly Pennsylvanian in age, whereas in the Northern Great Plains it is mostly sub-bituminous coal or lignite, and Cretaceous or Tertiary in age The plant material grew in the shallow water along the shore, dying in place, accumulated, and was buried, eventially forming peat As the peat was buried, the material compacted to coal and in doing so created a handy indicator to determine the depth of burial However, it never has been buried deep enough in the Continental Interior, or subjected to tectonic forces, to create the highest grade of coal, anthracite