A novel of manners is fiction work meant to re-create a social world with a very detailed observation the values, customs, and mores of a highly complex society.
A novel of sentiment is also called Novel of Sensibility and it reflects (1) an overindulgence in emotion, especially when it is the conscious effort of inducing emotion in order to enjoy it.
A novel of incident is dominated, usually, by episodic action.
Neither of those fit because Silas Marner is usually considered to be a novel of motives.