The Mercia Mudstone Group is an early Triassic lithostratigraphic group (a sequence of rock strata) which is widespread in Britain, especially in the English Midlands – the name is derived from the ancient kingdom of Mercia which corresponds to that area. It is frequently encountered in older literature as the Keuper Marl or Keuper Marl Series. * Blue Anchor Formation * Branscombe Mudstone Formation * Arden Sandstone Formation * Sidmouth Mudstone Formation * Tarporley Siltstone Formation