The manuscript of Middlemarch is in the British Library and sixteen pages are online here. In December 1870 George Eliot decided to combine  the chapters she had already written with  a new story called ‘Miss Brooke’: the BL manuscript consists of four notebooks containing the final, revised draft; originally written on loose leaves, they were later bound into volumes. There is a book about the composition of the novel, Jerome Beaty’s Middlemarch From Notebook to Novel (Athlone Press, 1967). It would be a fascinating exercise to reread Middlemarch with Beaty’s book to hand.