Waters which were

1:7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.

Who could have seen this coming after the "Let there be a firmament" in the previous verse?

This was predictable, but it adds to our knowledge in one specific way: the division was between low and high, "under" and "above".  Actually, a little startling.  When I picture water being divided, I see a left/right division.  This is interesting and different, but still not terribly informative, since we still have no clue as to what the firmament was.

One interesting point is that this is different from the creation of light.  Instead of the firmament just suddenly being, we now have God explicitly making it.  Which definitely points to God as a committee; why else say you want a firmament and then make it, unless you're one subcommittee communicating with another?

A less interesting point is that the last phrase "and it was so" is completely pointless.  What are the other options, " ... just kidding, no firmament"?