(Exodus 15:5) "so that the depths should cover them": Now are there depths there (at the bottom of the sea)? Is it not dry ground? What, then, is the intent of "should cover them"? — The lower depths (under the earth) ascended to the upper depths and the torrents embattled them. Thus, "the depths should cover them."
That the Depths Should Cover Them Now
Mekhilta Tractate Shirah 5:1