Question: What was the population as of the 1990 census of the town about which "Sky of Stone" was written?
Sentence (from "Walpack Township, New Jersey"): As of the 2010 United States Census, the township had a population of 16, reflecting a decline of 25 (-61.0%) from the 41 counted in the 2000 Census, which had in turn declined by 26 (-38.8%) from the 67 counted in the 1990 Census.
Relevant evidence: No