It became clear that there had been significant changes in the Earth's topography over time and that these changes could neither be accounted for by natural processes operating during the brief nor by the postulated Noachian flood.
Notable observations included: ran from about 1780-1850.
By the end of the 18'th century it was clear that the Earth had a long and varied history. The major debate was between the catastrophists, e.g., Cuvier, who held that the history of Earth was dominated by major catastrophic revolutions and the uniformitarians, e.g.
An unconformity is a gap in the sedimentary rock record.
This animation shows the formation of an angular unconformityone where the layers above and below the unconformity are not parallel to each other, but form an angle.