La Folia (= Spanish: Folía; French: Folie d’Espagne) is a well-known dance tune popular from the 16th century or earlier and found in the work of composers such as Corelli (1653–1713), who used the theme for a set of variations forming a violin sonata, or later by Rachmaninov (1873–1943) in his incorrectly named Variations on a Theme of Corelli. [..]

(n) a thin layer or stratum of (especially metamorphic) rock