Scientific exploration of what is now Kansas began at the start of the 19th Century. Explorers who touched or crossed present-day Kansas included Lewis and Clark (1804), Pike (1806), Nuttall (1809-1810), Long (1819-1820), Nicollet (1838-1839), and Frémont (1842, 1844, 1845). Their contributions are now of historical interest only.
Dr. F. A. Wislizenus crossed the area in 1846 and identified the Carboniferous near present-day Ottawa and the Cretaceous near the great bend of the Arkansas River. F. B. Meek and F. V. Hayden in 1856 identified rocks of Tertiary age, probably in north-central Kansas. Maj. Frederick Hawn collected fossils that were identified by Meek as being of Permian age. In 1858 Hawn and G. C. Swallow published just 13 days before Meek and Hayden presented their paper. In the same year Swallow and Hawn presented the first stratigraphic column for Kansas. This column also introduced the term Quaternary, and included Cretaceous, Permian, and Carboniferous; it incorrectly included Triassic but omitted Tertiary.
By 1904 C. S. Prosser and J. W. Beede reclassified the Carboniferous rocks near Cottonwood Falls, and identified these as Pennsylvanian. C. E. Siebenthal introduced the term Mississippian in 1907 for rocks in the southeastern corner of the state. He also assumed that rocks of Cambrian and Ordovician ages were present in the subsurface. In southwestern Kansas, outcrops along the Cimarron River have been variously mapped as Cretaceous, Triassic, Jurassic; they now are considered Triassic.