After meeting Tom for the last time, Nick goes back to his house and notices that Gatsby's grass is as long as his own. Gatsby's yard and his mansion used to be well kept. Gatsby had tried to create a magical, glorious world around himself. This was part of his allure, his way of impressing Daisy. Now that the grass is long and Gatsby is gone, it shows that the allure is gone too. The image is depressing to Nick.
During his last night at the house, Nick notices a curse word on Gatsby's steps. It is another reminder of the glory being gone. Nick erases the word. Nick gazes upon the water and imagines what the land looked like before all the houses and buildings were there. He says the houses "melt away until gradually I became aware of the old island here that flowered once for Dutch sailors’ eyes—a fresh, green breast of the new world." He is thinking of how North America (the new world) was once a tabula rasa in the eyes of European explorers. In other words, it was a blank canvas, a glorious natural world that seemed to evoke promise and dreams. In contrast, modern America offers the same promise, but the American Dream is difficult if not impossible for some. Gatsby's dream eventually failed.
Nick associates this fresh, green, natural world full of promise with the green light at the end of Daisy's dock. Here, the color green suggests vibrant life, the flowering of plants and trees. "And as I sat there brooding on the old, unknown world, I thought of Gatsby’s wonder when he first picked out the green light at the end of Daisy’s dock." The mood is solemn, even depressing. Gatsby's green light represented the hope and potential of a dream. The dream ended in tragedy. The fresh, green land of old world America represented the "American Dream" to explorers and later, to immigrants. Like Gatsby, many of those immigrants did not see their dreams realized. This notion of dreams unrealized is part of Fitzgerald's critique of the American Dream. To those explorers who first came to America, the great green landscape looked full of promise. Fitzgerald questions if America has lived up to that promise.