The earth shook, the heavens also dropped, at the presence of God (see Exodus 19:16-18; Deuteronomy 5:22, Deuteronomy 5:23). The "dropping" of the heavens was the descent of a thick thundercloud upon the mount, which rested upon it, and spread around a dense and weird darkness.
Even Sinai itself was moved at the presence of God; literally, yonder Sinai, as if it were in sight, and could be pointed at. The God of Israel. Our God, who did all these great things for us.