A theological controversy which arose in Scotland in the 18th century over the teaching of a book entitled "The Marrow of Modern Divinity," and which led to a secession from the Established Church on the part of the "Marrow men," as the supporters of the doctrine of the book were called. It contained an assertion of the evangelical doctrine of free grace, which was condemned by the Assembly, and for maintaining which the "Marrow men," headed by the Erskines, were deposed in 1733, to the formation of the Secession Church.