Sentence:  And as I sat there <WSD>brooding</WSD> 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. He had come a long way to this blue lawn, and his dream must have seemed so close that he could hardly fail to grasp it. 
Meaning of the word marked with <WSD> tags:  To dwell upon moodily and at length (with adpositions generally being either about or over), mainly alone.