But here a question arises: If the flood transcended the highest mountains of the earth by fifteen cubits, then it was raised up to the middle region of the air. For we see not rarely that, around the peaks of lofty mountains, clouds are gathered and rains are generated — as though in that place is the middle region of the air, which is the natural place of the generation of rains. But if the flood filled the middle region of the air, it could not have had those waters from rains, since it surpassed the place of the generation of rains. Whence, then, did it have the waters by which it grew so [much]…¹

…by which it grew so much? It can be answered in two ways. First, by denying that the flood reached the middle region of the air, which is farther distant from the earth than the flood ascended. And the generation of rain around the peaks of mountains happens accidentally — namely, when the clouds, [gathered] densely with many and thick vapors, much cold being found there, are condensed and resolved into rain; or, driven and compressed thither by the winds, are similarly turned into water. Next, it can be answered that the flood did indeed reach the middle region of the air, but only as far as pertains to the lowest part of that region, nearest to the lands. But the other, higher part of that region was above the flood, since it extends so widely that its end is very far distant from the lands: for the Mathematicians make the third region of the air to be distant fifty miles from the lands. Therefore, from the waters generated in the higher part of the middle region, an increase could come to the flood, up to the lowest part of the middle region of the air.²

But on the occasion of this passage which we are treating, that passage which is in St. Peter about the heavens which perished by the flood must be explained in passing; for it has no small kinship with this passage of Moses. St. Peter, in the last chapter of his second Epistle, signifies that the heavens perished by the flood, and again that they, restored after the flood, are reserved for fire unto the day of judgment. But it is asked, of which heavens he speaks? St. Peter certainly did not speak of the starry heavens: both because the flood was raised on high only to fifteen cubits above the mountains of the earth, whence to the stars there is an almost immense distance; and also because, although the flood had reached up to heaven, yet, since heaven is incorruptible, it could have taken no detriment from it. It remains, therefore, that St. Peter spoke of the airy heavens — and not of the whole air, since above that place to which the flood ascended there is a very wide region of air, wholly untouched by the waters of the flood.³

Therefore the statement of St. Peter must be interpreted of the lowest part of the air, nearest to the lands. For since the flood was raised over the whole earth so far that it surpassed the highest mountains by fifteen cubits, it was necessary that the air which entirely occupied all that space around the earth, filled by the flood, either was corrupted and changed into water, contributing to the increase of the flood; or, yielding to the waters, withdrew itself upward, the heavens yielding place to it. But this latter is absurd and incredible. For the situation, disposition, and motion of the celestial spheres is by nature entirely unchangeable, and there was no reason why it should be changed at the time of the flood. Wherefore it is truer to say that all that air was converted into water. And this too is most likely: that as great a space of air as the flood occupied, so great also the conflagration will occupy at the consummation of the world.⁴

But I am pleased to confirm and adorn this opinion of ours by the authority and words of St. Augustine. Thus he writes in the third book On Genesis according to the Letter, chapter two: “That the airy heavens perished, in a manner, by the flood, we read in a certain one of those [Epistles] which are called canonical. For that moist nature, which had so grown that it transcended the peaks of the highest mountains by fifteen cubits, could not have reached the stars: but because it had filled the whole, or nearly the whole, spaces of this moister air in which the birds fly, the heavens which had been are written, in that Epistle, to have perished: which I do not know how it can be understood, except [with] the quality of this thicker air convert[ed] into the nature of waters…”⁵

“…except [with] the quality of this thicker air converted into the nature of waters. Otherwise these heavens would not then have perished, but would have been raised higher, when the water occupied their place. And so we more easily believe, according to the authority of that Epistle, that they perished, and that others (as is there written) were put in their place — the exhalations, namely, being rarefied — than that they were so raised up that the nature of the higher heaven yielded its place to them. For water is so similar to this air, that it is proved to grow thick by its exhalations, so that it both makes the breath of a storm — that is, draws together wind and clouds — and can sustain the flight of birds.”⁶

“Wherefore, even if a certain one of the secular poets spoke truly: ‘Olympus rises above the clouds,’ and, ‘The heights hold peace’ — because it is reported that on the peak of Olympus the air is so thin that it is neither overshadowed by clouds, nor disturbed by winds, nor can sustain the flight of birds, nor nourish with the breath of [its] thicker air those men who perchance have ascended, as they are accustomed to be nourished in this [lower] air — and yet it too is air, whence by a quality akin to waters it is diffused, and on that account it too is believed to have been converted into a moist nature at the time of the flood. For it is not to be thought that the water usurped anything of the spaces of the starry heaven, since it transcended even all the highest mountains.” So Augustine. But whether the flood inundated, laid waste, and destroyed the earthly Paradise, has been disputed by us in the former volume of our Commentaries on Genesis in two places — both in book 3, question five, and especially in book 7, the last question: where we also treated clearly and diligently this passage of Genesis about which we now dispute.⁷