To setup 2 layers (e.g. 1.5 meters of overburden over hardpan) you must enter 2 ground types and 1 depth. The depth is ignored unless the ground type for the layer below is defined.
To setup 3 layers you must enter 3 ground types and 2 depths.
NOTE: The bottom layer is always assumed to be infinitely deep.
Edit
The Edit Button accesses the Ground Types Editor allowing you to add or modify Ground Types.