Gilbert, (Sir) W(illiam) S(chwenck) (b London, 1836; d Harrow Weald, 1911). Eng. poet and playwright, librettist of 14 operettas (the ‘Savoy Operas’) with Sullivan from 1871 to 1896. Knighted 1907. The libretti for Sullivan were: Thespis (1871); Trial by Jury (1875); The Sorcerer (1877, rev. 1884); HMS Pinafore (1878); The Pirates of Penzance (1879); Patience (1881); Iolanthe (1882); Princess Ida (1884); The Mikado (1885); Ruddigore (1887); The Yeomen of the Guard (1888); The Gondoliers (1889); Utopia (Limited) (1893); The Grand Duke (1896).

Gilbert A reversed polarity chron in the mid Pliocene, which is followed by the Gauss normal polarity chron. It started about 5.70 Ma ago and lasted until 3.58 Ma. The Gilbert contains at least four normal polarity subchrons: Thvera; Sidufjall; Nunivak; and Cochiti.