Genesis 1:9

(9) Let the waters be gathered together.—The verb, as Gesenius shows, refers rather to the condensation of water, which, as we have seen, was impossible till the surface of the earth was made cool by the radiation of heat into the open expanse around it.

Unto one place.—The ocean bed. We must add the vast depth of the ocean to the height of the mountains before we can rightly estimate the intensity of the forces at work on the third day. Vast, too, as the surface of the ocean may appear compared with the dry land, it is evidently only just sufficient to supply the rain necessary for vegetation. Were it less, either the laws of evaporation must be altered, with painful and injurious effects, or much of the earth’s surface would be barren.

Let the dry land appear.—Simple as this might appear, it yet required special provision on the part of the Creator; for otherwise the various materials of the earth would have arranged themselves in concentric strata, according to their density, and upon them the water would have reposed evenly, and above it the air. But geologists tell us that these strata have been broken up and distorted from below by volcanic agencies, while the surface has been furrowed and worn by the denuding power of water. This was the third day’s work. By the cooling of the crust of the earth the vast mass of waters, which now covers two-thirds of its surface, and which hitherto had existed only as vapour, began to condense, and pour down upon the earth as rain. Meanwhile the earth parted with its internal heat but slowly, and thus, while its crust grew stiff, there was within a mass of molten fluid. As this would be acted upon by the gravity of the sun and moon, in just the same way as the ocean is now, this inner tidal wave would rupture the thin crust above, generally in lines trending from northeast to south-west. Hence mountain ranges and deep sea beds, modified by many changes since, but all having the same final object of providing dry land for man’s abode.