And God said,
Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
All Commentaries on Genesis 1:6 Go To Genesis 1
Basil the Great
And surely we need not believe, because [the firmament] seems to have had its origin, according to the general understanding, from water, that it is like either frozen water or some such material that takes its origin from the percolation of moisture, such as is a crystalline rock.