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In various revised editions ( 12 in all , through 1872 ) , " Principles of Geology " was the most influential geological work in the middle of the 19th century , and did much to put geology on a modern footing .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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