Explanation:

Erosional Landforms by Groundwater :

• On the surface of the limestone are numerous swallow holes, which are small depressions carved out by solution where rain-water sinks into the limestone at a point of weakness. They are also known as sink holes.
• Once water has sunk into the limestone it etches out caverns and passages along joints or bedding planes.
• Where a number of swallow holes coalesce a larger hollow is formed and is called a Doline .
• Several Dolines may merge as a result of subsidence to form long, narrow to wide trenches called valley sinks or Uvala. Some of them are a mile across, containing much clayey soil from the limestones, weathered after their subsidence.  Gradually, most of the surface of the limestone is eaten away by these pits and trenches, leaving it extremely irregular with a maze of points, grooves and ridges or Lapies. Especially, these ridges or lapies form due to differential solution activity along parallel to sub-parallel joints. The lapie fi eld may eventually turn into somewhat smooth limestone pavements.