Other metaphors in Martin Luther King's "I Have a Dream" speech include:
"Seared in flames of withering injustice," which compares injustice to the flames of a fire.
"Joyous daybreak" ending the "long night of their captivity," which uses light to symbolize freedom and night to represent enslavement.
"Lonely island of poverty," uses an island to represent poverty, and therefore isolation. This is followed by "vast ocean of material prosperity," which compares material prosperity to an ocean.
"To cash a check" refers to African-Americans coming to claim the freedom they were promised; this is complemented by "signing a promissory note," which refers to the freedom promised by the founding fathers under the Declaration of Independence. The speech then states that every American was to "fall a heir" to this independence, highlighting how not all Americans have benefited from the Declaration of Independence.
"Storms of persecution" highlights how being persecuted as an African-American was stormy.