When the dust groweth into hardness - Margin, "is poured, or, is turned into mire." The words used here relate often to metals, and to the act of pouring them out when fused, for the purpose of casting. The proper idea here is, "when the dust flows into a molten mass;" that is, when wet with rain it flows together and becomes hard. The sense is, that the rain operates on the clay as heat does on metals, and that when it is dissolved it flows together and thus becomes a solid mass. The object is to compare the effect of rain with the usual effect in casting metals.
And the clods cleave fast together - That is, they are run together by the rain. They form one mass of the same consistency, and then are baked hard by the sun.

When the dust groweth into hardness - That is, Who knows how the dust - the elementary particles of matter, were concreted; and how the clods - the several parts of the earth, continue to cohere? What is the principle of cohesion among the different particles of matter, in all metals and minerals? Even water, in a solid form, constitutes a part of several gems, called thence water of crystallization. Who can solve this question? How is it that 90 parts of alumine, 7 of silex, and 1.2 of oxide of iron, constitute the oriental ruby? and that 90 parts of silex and 19 of water, form the precious opal? And how can 46 parts of silex, 14 of alumine, 28 of carbonate of lime, 6.5 of sulphate of lime, 3 of oxide of iron, and 2 of water, enter into the constitution, and form the substance, of the lapis lazuli? How do these solids and fluids of such differing natures grow into hardness, and form this curious mineral? Take another example from that beautiful precious stone, the emerald. Its analysis shows it to be composed of glucine 13, silex 64.5, alumine 16, lime 1.6, and oxide of chrome 3.25. Now how can these dusts, utterly worthless in themselves, grow into hardness, combine, and form one of the most beautiful, and, next to the diamond, the most precious, of all the gems? The almighty and infinitely wise God has done this in a way only known to and comprehensible by himself.

When the dust groweth into hardness, (z) and the clods cleave fast together?
(z) For when God does not open these bottles, the earth comes to this inconvenience.

When the dust groweth into hardness, and the clods cleave fast together? When the dust is attenuated, and ground, as it were, into powder; and the clods cleave together, as if glued, as in a drought for want of rain: or the bottles of heaven being unstopped and poured out; or
"sprinkling the dust with this sprinkling,''
as Mr. Broughton. Or rather, pouring on the dust with pouring; that is, pouring down rain, by unstopping the bottles of heaven. The dust, as meal, by water poured into it, cements, unites, and is compacted, and becomes earth, that may be cultivated; is clodded and cleaves together, and may be ploughed and sown.

groweth, &c.--rather, pour itself into a mass by the rain, like molten metal; then translate Job 38:38, "Who is it that empties," &c., "when," &c.? The English Version, however, is tenable: "Is caked into a mass" by heat, like molten metal, before the rain falls; "Who is it that can empty the rain vessels, and bring down rain at such a time?" (Job 38:38).

Mire - By reason of much rain.