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The Carraways are something of a clan, and we have a tradition that we're descended from the Dukes of Buccleuch, but the actual founder of my line was my grandfather's brother, who came here in fifty-one, sent a substitute to the Civil War, and started the wholesale hardware business that my father carries on to-day. (1.5)
Nick self-deprecatingly punctures the illusion that his family comes from nobility—but instead, he makes himself into another kind of nobility: a family that actually has achieved the American Dream of wealth and respectability through hard work.
I lived at West Egg, the—well, the less fashionable of the two, though this is a most superficial tag to express the bizarre and not a little sinister contrast between them. [...] Across the courtesy bay the white palaces of fashionable East Egg glittered along the water, and the history of the summer really begins on the evening I drove over there to have dinner with the Tom Buchanans. Daisy was my second cousin once removed, and I'd known Tom in college. And just after the war I spent two days with them in Chicago. (1.14-15)
Nick sees two kinds of America: the hard-working Chicago, part of a "Middle-West" culture; and the "white," fashionable East Egg. Nick may be able to make it in the Middle-West, but he's not cut out for East Coast life.
I decided to call to him. Miss Baker had mentioned him at dinner, and that would do for an introduction. But I didn't call to him, for he gave a sudden intimation that he was content to be alone—he stretched out his arms toward the dark water in a curious way, and, far as I was from him, I could have sworn he was trembling. Involuntarily I glanced seaward—and distinguished nothing except a single green light, minute and far away, that might have been the end of a dock. When I looked once more for Gatsby he had vanished, and I was alone again in the unquiet darkness. (1.152)
We never see Gatsby's version of America directly; we just get glimpses of it through Nick's narrative and through ephemera like his childhood notebook. But, judging from the way he's staring across the water, Gatsby has a pretty spectacular vision.