I want to know the answer to the following question:
What was used in the mid-19th century to explain the presence of "folded" mountain chains?
All the background I'm provided with is that "In the mid-19th century the now defunct theory of geosynclines was used to explain the presence of "folded" mountain chains but by the mid-20th century the theory of plate tectonics became widely accepted.". Is that enough to answer the question?
Answer: yes