Syntax

In the beginning of Chapter II Fitzgerald first introduces the Valley of Ashes, a dumping ground of ashes that is depicted to be dark and gray. Fitzgerald states, 

This is a valley of ashes--a fantastic farm where ashes grow like wheat into ridges and hills and grotesque gardens; where ashes take the forms of houses and chimneys and rising smoke and, finally with a transcendent effort, of men who move dimly and already crumbling through the powdery air. Occasionally a line of gray cars crawls along an invisible track, gives out a ghastly creak, and comes to rest, and immediately the ash-gray men swarm up with leaden spades and stir up an impenetrable cloud, which screens their obscure operations from your sight (Fitzgerald 23).

In this passage Fitzgerald uses compound-complex sentences to illustrate the Valley of Ashes and this technique helps the reader picture it in their own mind. He could have made these two sentences into several more sentences but Fitzgerald merges them together to continue his description of the desolate area.