Stairhole: marine action has breached the outer protective layers of Portland and Purbeck Limestone and eroded the softer Wealden Beds behind.  Differential erosion has produced caves in the outer wall slumps and flows move the Wealden Beds closer to the waterline. Students fieldsketching at Lulworth Cove.  Here, marine action has eroded back as far as the chalk that now forms the back wall of the cove.  It is likely that meltwater streams played a part in the initial breakthrough of the outer limestone layers while subsequent sea level rise then flooded it. Walking west away from Lulworth Cove towards Durdle Door.  The village of Lulworth and Bindon Hill, the chalk ridge that forms the back wall of Lulworth Cove, are clearly visible, with Mupe Bay beyond. Man O War Rocks - the eroded remnants of the Portland / Purbeck limestone barrier.  Note how the protected chalk cliff immediately behind the rocks is relatively shallow and vegetated, showing that the steep white appearance of many chalk cliffs is only preserved by regular erosion at the base. The fine bedding of the Purbeck limestone is very visible on the beach at Durdle Door.  These rocks were once part of the much larger Purbeck anticline and their vertical arrangement has been central in determining the shape of this coastline. The chalk cliffs between Durdle Door and Bat's Head are actively eroding and prone to large rock falls.  The small arch and stack in the distance indicate the differential erosion affecting the chalk