Silas Marner ends with a wedding, a curiously optimistic send-off for a novel that has led its protagonist Silas (and its secondary protagonist Godfrey) through one misfortune after another. The pat ending—Eppie sighing delightedly that "nobody could be happier than we are"—should satisfy even the pickiest romantic.
But—just before the wedding, Eppie and Silas head off to the big city to discover what's become of Silas's old community and to try to ferret out the truth of what went on when Silas was accused of theft. But Lantern-Yard is gone, and in its place is a factory. Nothing remains of Silas's old community, no one has any information, and Silas never does get closure. That dull spot on the otherwise shiny ending is just one clue that Eliot drops for us to follow to a darker conclusion.
As Godfrey reminds Silas, he's not able to make as much money as he used to, because the same kind of factories that have replaced Lantern-Yard are going to start replacing the Silases of England. Industrialization is coming, and the pastoral idyll that Eliot depicts will become nothing more than a story—one that sounds very similar to the Merry (or "Merrie") England myth that depicts pre-Industrial England as a pastoral utopia that existed before industrialization.
So, you could just accept the pretty cottage at face value as a happy ending. There's definitely evidence in the text to support that reading. But we can't shake the feeling that Eliot wouldn't end a book that way. Literary critics (and mathematicians) say that something is "overdetermined" when you get the same result from doing something in more than one way. In less precise terms, something is "overdetermined" when it's just a little too obvious. What we're suggesting is that this ending is overdetermined: it's just a little too obvious to be believed.