Charles Ellicott Commentary Job 28:9

"He putteth forth his hand upon the flinty rock; He overturneth the mountains by the roots." — Job 28:9 (ASV)

He putteth forth his hand upon the rock. —The process described is that of tunnelling and excavating, and that of making canals and lining them with stone; and in the course of such works many precious things would be discovered. The canals and cisterns were made so accurately that they retained the water, and did not even weep or trickle.