sentences:  On top of the Nether Alderley Sandstone lie the Mercia Mudstones which attain a thickness of 300 m, but these are only seen on the lower plains, it is in these beds that the halite lies.Mottling in the red blocky mudstone is of two main types,
  
  
  The ferruginous colour pigmenting is finely disseminated over the surface of individual grains and accounts for a very small percentage of the rock.It is thought that where the rock is grey or grey green either from primary or secondary causes, the oxide has been chemically removed during deposition and thus unmasking the true colour of the minerals in the sediment.