Albert Barnes Commentary Jeremiah 13:4

"Take the girdle that thou hast bought, which is upon thy loins, and arise, go to the Euphrates, and hide it there in a cleft of the rock." — Jeremiah 13:4 (ASV)

In a hole of the rock - “In a cleft of the rock.” As there are no fissured rocks in Babylonia, the place where Jeremiah hid the girdle must have been somewhere in the upper part of the river.