In Chapter 19, when Godfrey Cass and Nancy offer Eppie a home and reveal that Godfrey is her true father, Silas is horrified at the prospect of having another Cass steal his "gold" from him. This time, though, it's because he has become a father in every way that matters to Eppie, and Eliot uses a metaphor to underline how seriously he takes that relationship:
‘Just the same?’ said Marner, more bitterly than ever. ‘How’ll she feel just the same for me as she does now, when we eat o’ the same bit, and drink o’ the same cup, and think o’ the same things from one day’s end to another? Just the same? that’s idle talk. You’d cut us i’ two.’ Godfrey, unqualified by experience to discern the pregnancy of Marner’s simple words, felt rather angry again.
Although Silas could not literally have been "pregnant" with Eppie, his speech to Godfrey reveals that he loves Eppie as though he had birthed her himself. Just as he can't be her mother, he isn't her biological father. However, the reality of the blood relationship is as immaterial to Silas as the distinction between a mother and a father's love. He loves Eppie like a father regardless of Godfrey's biological connection to her. The wordplay of "pregnant" is verbally ironic here, because of the paternal relationship both men have with Eppie. It's also ironic because of what happened to Molly. The last time Godfrey was able to "discern a pregnancy" when Eppie was involved, he did not behave in a fatherly or exemplary way.
Silas doesn't want to take the gold back, when Godfrey offers it just before this exchange, because he doesn't need it. This is partially because the money doesn't matter to him now that he has Eppie, and also because Godfrey doesn't understand what it is he is offering. Giving the gold to Silas and taking Eppie away would essentially be an exchange of one "gold" for another.
