Hi greg spahn,
Per the support article Read books in the Books app on iPad:
"Change the text and page appearance
- Tap the page, tap
at the bottom of the page, tap Themes & Settings, then do any of the following:
- Change the font size: Tap the large A to increase the font size or tap the small A to decrease it.
- Change the font: Tap Options, tap Font, select a font option such as Georgia or Palatino, then tap Done.
- Turn on vertical scrolling: Tap
to scroll continuously through a book.- For PDFs, tap
, at the top of the screen then turn on Vertical Scrolling. - Adjust the display brightness: Tap
, then choose an option. - Change the page background color: Tap a page theme such as Quiet or Bold.
- Make the font bold: Tap Options, then turn on Bold Text (green is on).
- Customize spacing and justification: Tap Options, turn on Customize (green is on), then drag the sliders left or right to adjust line spacing, character spacing, and word spacing. You can also turn Full Justification and Allow Multiple Columns off or on (green is on).
2. Tap Done to apply your changes."
The only selection mentioned on that page under the icon you describe is "Vertical Scrolling", try the listed steps to change display options.
Regards.