question: What was used in the mid-19th century to explain the presence of `` folded '' mountain chains ?
answer: theory of geosynclines
turker_answer: The theory of geosynclines was used in the mid-19th century to explain the presence of `` folded mountain chains '' .
rule-based: Theory of geosynclines was used in the mid-19th century to explain the presence of `` folded '' mountain chains .