'Rocks' in the Bible

and the kings of the earth, and the great men, and the rich, and the chiefs of thousands, and the mighty, and every servant, and every freeman, hid themselves in the dens, and in the rocks of the mountains,

and they say to the mountains and to the rocks, 'Fall upon us, and hide us from the face of Him who is sitting upon the throne, and from the anger of the Lamb,'