12. Smith, J. R. — Industrial and Commercial Geog- 



raphy, Chapter II. 



13. Trimble, W. J. — The Agrarian History of the 



United States as a Subject for Research, in 

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 90. 



14. Turner, F. J. — The Significance of the Frontier 



in American History, in Annual Report of the 

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The Frontier in American Development, in 

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The Problem of the West, in The Atlantic 

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15. Walker, F. A. — The General Characteristics of 



American Agriculture, Tenth Census, Vol. Ill, 

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