The waters are hid as with a stone; rather, the waters are hardened, like unto stone. When the frost comes, the waters are congealed and rendered as hard as stone. (So Dillmann and Canon Cook.) And the face of the deep is frozen.
By "the deep" ( תּהוֹם) is certainly not meant here either the open ocean, which, in the latitudes known to the dwellers in South Western Asia, never freezes, or the Mediterranean. Some of the lakes which abound in the regions inhabited by Job and his friends are probably meant.
These may occasionally have been thinly coated with ice in the times when the Book of Job was written (see the comment on Job 6:16).