'Rocks' in the Bible

Then the kings of the earth and the great men and the military commanders and the wealthy and the strong and everyone, [whether] slave or free, hid themselves in the caves and among the rocks of the mountains;

and they called to the mountains and the rocks, “Fall on us and hide us from the face of Him who sits on the throne, and from the [righteous] wrath and indignation of the Lamb;