Why does Fitzgerald contrast hard rock with wet marshes what does he mean?

Fitzgerald contrasts hard rock with wet marshes to highlight the dichotomy between stability and instability, as well as the tension between aspiration and reality. The hard rock symbolizes strength, permanence, and the American Dream's allure, while the wet marshes represent the elusive, often deceptive nature of that dream, filled with uncertainty and decay. This juxtaposition serves to illustrate the characters' struggles and the broader social commentary on the fragility of success and the inherent challenges of navigating life's complexities. Ultimately, it reflects the tension between ambition and the often harsh realities that undermine it.