Complex sentence: The land that is now Westchester Township was once completely covered by the Wisconsin Ice Sheet, and then submerged beneath Lake Chicago during one other notable period of the ice sheet's recession from around Indianapolis to the arctic region where it currently resides.
Split into simpler sentences: The land that is now Westchester Township was once completely covered by the Wisconsin Ice Sheet. Later on, it was submerged beneath Lake Chicago during one other notable period of the ice sheet's recession from around Indianapolis to the arctic region where it currently resides.