Describing Silas Marner as slice-of-life realism is not quite fair—it's a lot more than that—but many critics have noticed the "Dutch realism" of her writing here. Dutch realism refers to paintings in the 17th century that focused on images of domestic, often interior life, rather than Biblical or classical scenes. Eliot's use of dialect, like this first instance "Some folks 'ud say that was a fine beast you druv in yesterday, Bob?" (1.6.2), has a lot to do with the book's air of realism. Eliot was trying to represent not stereotypical country people but a specific kind of dialect—like Mark Twain representing Jim and Huckleberry's speaking voices in The Adventures of Huckleberry Finn.
The realism also comes through in the careful attention Eliot pays to the everyday facts of village life, describing the tools of Silas's trade, the piles of laundry that Mrs. Winthrop washes, the humdrum conversations of men at the pub, and the sneers of city folk laughing at Nancy's dialect. As a writer of realism, Eliot was participating in the 19th century's dominant form of novel writing. The great masters of the mid-1800s—Dickens, Trollope, the Brontës, Thackeray—were all, in various ways, realists: they wanted to represent truth by describing common, everyday life rather than the aristocratic adventures that had been popular before novels became the dominant form of literature.