"Let's model me a mine"
M.E.G.M.S.
Mining & Exploration Geological Modelling Services
Insert command (Tools menu and Toolbar) 
Select this to select the Insert Tool. When using the Insert tool
the mouse cursor changes to a stylised "i" (
) and "Insert" is displayed in the MEGS_Log
status bar.
When using the Insert tool you can left click with a unit to create a new boundary and split the unit in two. If you click and drag, then two boundaries are created, with the lower boundary tracking the mouse.
The current Insert Mode changes the way in which the Insert tool behaves - when the Insert Mode is Insert, the Insert tool shift units below the newly inserted unit down, maintaining the thickness of the immediately underlying unit, otherwise the Insert tool changes the thickness of the immediately underlying unit, and maintains the same depth for all following units.
The shortcut key for this command is F6. You can cancel the Insert tool and return to Normal mode by pressing the Escape key.
See About Editing Tools for more information.