And God said, “Let the waters under the heavens be gathered together into one place, and let the dry land appear.” And it was so.
9. Let the waters... be gathered together This also is an illustrious miracle, that the waters by their departure have given a dwelling-place to men. For even philosophers allow that the natural position of the waters was to cover the whole earth, as Moses declares they did in the beginning; first, because being an element, it must be circular, and because this element is heavier...
The third day's work is related in these verses - the forming of the sea and the dry land, and the making of the earth fruitful. Hitherto the power of the Creator had been exerted and employed about the upper part of the visible word; the light of heaven was kindled, and the firmament of heaven fixed: but now he descends to this lower world...
Commenting on Genesis 1:9-13
And God said, let the waters under the heaven be gathered together unto one place,.... Which are before called the waters under the firmament; and which were either on the surface of the earth, or in the bowels of it, or mixed with it, which by the compressure of the expanse or air were separated from it and these, by apertures and channels made, were...