Sentence:
incautiously held it upright, whereupon the tobacco fell out ON TO the floor (George Orwell, 1984. Page #8)
Additional information:
I know that when we describe some movement (e.g. into the room, onto the bus, onto the shelf, onto the bed) we always should use preposition of movement (into, onto etc)
Question:
Why is 'on' separated with 'to' in the sentence