vertical split in main working area?

Hello all, I recently had a splitter bar that places track in the top and bottom of the project area each with its own scroll bar. I can see how this could be useful for track management, but it is driving me batty and I can’t figure out what I did to make it appear. Attaching a pic. Thanks!
cubase split.JPG

“Divide track list” PDF Manual p.40. The horizontal-line symbol on top of the track list in your screenshot.

Thinking Cap, You are a genius! Thanks so much. I somehow have never noticed that little button. :smiley: