Cosmas Indicopleustes, on Gen 1:6

“And God said: Let there be a firmament made amidst the waters: and let it divide the waters from the waters.”

“On the second day God said: Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. He made this heaven, not the one above, but the visible heaven which he crystallised from the waters like ice. But I shall endeavour to place the matter before your eyes, for many things are better explained by ocular than by oral demonstration. This water, let us suppose, overflowed the earth five cubits. Then God said: Let there be a firmament in the midst of the water, and thereupon a solid ice-like substance was produced in the midst of the waters, which made lighter the upper half of the water, and left the other half underneath, as it is written: Let there be a firmament in the midst of the water, and let it make a division between the waters. But wherefore does he call it the firmament? It is, because God made it firm and solid from waters which are of rarer and less compact substance. Wherefore David also says: Praise him in the firmament of his power; and, to take another example, we may adduce smoke, which when emitted from burning wood is rarified and attenuated, but when it mounts up high into the air becomes transformed into the density of a cloud. In this wise, when God had made the waters, which are by nature rarified, ascend on high, He there made them solid. And that this example is to the point, and true, Isaiah testifies where he says: The heaven was made firm and solid as smoke. The heaven having therefore become solid in the midst of the waters made the upper half of them light, but the other half He left underneath. Why then and for what purpose were the waters placed above? Was it that we might drink them or that we might sail on them? For that there are waters above, David testifies, saying: And the water which is above the heavens.”

Imported from an open dataset — not yet checked against the printed edition.