Complex sentence: What would have been the crossing and transcepts became a continuation of the reading room and two-story stacks, but, in place of an apse, Keller added the Great Hall, a large meetingroom perpendicular to the building's axis.
Split into simpler sentences: What would have been the crossing and transcepts became a continuation of the reading room and two-story stacks. In place of an apse, Keller added the Great Hall, a large meetingroom perpendicular to the building's axis.