Sentence:  But Claggart's was no vulgar form of the passion. Nor, as directed toward Billy Budd, did it partake of that streak of apprehensive jealousy that marred Saul's visage perturbedly <WSD>brooding</WSD> on the comely young David. Claggart's envy struck deeper. 
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.