Sentence:  It was possible, I reflected, that a mere different arrangement of the particulars of the scene [of the House of Usher], of the details of the picture, would be sufficient to modify, or perhaps to annihilate its capacity for sorrowful impression; and, acting upon this idea, I reined my horse to the precipitous brink of a black and lurid <WSD>tarn</WSD> that lay in unruffled lustre by the dwelling, and gazed down—but with a shudder even more thrilling than before—upon the re-modelled and inverted images of the gray sedge, and the ghastly tree-stems, and the vacant and eye-like windows. 
Meaning of the word marked with <WSD> tags:  A small mountain lake, "especially" in Northern England. (from late 14th c.)