9 Do you suppose that a heavier body prevents the earth from falling into the abyss? Then you must consider that this support needs itself a support to prevent it from falling. Can we imagine one? Our reason again demands yet another support, and thus we shall fall into the infinite, always imagining a base for the base which we have already found. And the further we advance in this reasoning the greater force we are obliged to give to this base, so that it may be able to support all the mass weighing upon it.
Put then a limit to your thought, so that your curiosity in investigating the incomprehensible may not incur the reproaches of Job, and you be not asked by him, “Whereupon are the foundations thereof fastened?” If ever you hear in the Psalms, “I bear up the pillars of it;” see in these pillars the power which sustains it. Because what means this other passage, “He has founded it upon the sea,” if not that the water is spread all around the earth? How then can water, the fluid element which flows down every declivity, remain suspended without ever flowing?
You do not reflect that the idea of the earth suspended by itself throws your reason into a like but even greater difficulty, since from its nature it is heavier. But let us admit that the earth rests upon itself, or let us say that it rides the waters, we must still remain faithful to thought of true religion and recognise that all is sustained by the Creator's power. Let us then reply to ourselves, and let us reply to those who ask us upon what support this enormous mass rests, “In His hands are the ends of the earth.” It is a doctrine as infallible for our own information as profitable for our hearers.
Source: Nine Homilies of Hexaemeron (New Advent)