With this feature...
Do this...
formation mnemonic
For generic tops, select Generic User Top below and either type a mnemonic or click Formation Lookup Table to select one that exists in the current project.
For AccuMap user tops, select AccuMap User Top below and then click Formation Lookup Table to select one from the AccuMap formation top table. The AccuMap user tops database is updated when you place the top.
Formation Lookup Table
Click to display the Formation Lookup dialog box for either generic or AccuMap user tops (depending on which is selected below) and type the desired mnemonic. The display area highlights the mnemonic that most closely matches the letters you type.
AccuMap User Top 
Generic User Top
(Available in AccuMap DB mode)
Select whether to display results from the AccuMap formation tops table or tops specific to the current project. Selecting Generic User Top also enables you to type a new mnemonic directly in the formation mnemonic box above.
formation top
Type a depth at which to position the top.
invisible
Select to hide the top in the cross section.
rock or saturation type
Type or select a rock type or saturation type.