Sentence:  Much of the land is tundra, a mass of spongy, waterlogged clumps of sphagnum moss called tussock, muskeg, hummock, or in the vernacular of old-time Alaskans “<WSD>niggerheads</WSD>.” 
Meaning of the word marked with <WSD> tags:  A tussock (clump of plant material), found on tundra.