15. Rowland, Dunbar. The Mississippi Valley in 



American History, in Proceedings of the Mis- 

 sissippi Valley Historical Association, Vol. 

 IX, Part I (1915-1916), pp. 59-74. 



16. Semple, E. C. American History and Its Geo- 



graphic Conditions, Chapter IX. 



17. Shambaugh, B. F.The History of the West and 



the Pioneers, in the Proceedings of the State 

 Historical Society of Wisconsin, 1910, pp. 

 133-145. 



18. Turner, F. J. The Significance of the Frontier 



in American History, in Annual Report of the 

 American Historical Association, 1893, pp. 

 199-227. Reprinted in Bullock, Selected 

 Readings in Economics, pp. 23-59. 



The Frontier in American Development, in 

 McLaughlin and Harts Cyclopedia of Ameri- 

 can Government, Vol. II, pp. 61-64. 



The Problem of the West, in The Atlantic 

 Monthly, Vol. 78, pp. 289-297. 



The Significance of the Mississippi Valley in 

 American History. Proceedings of the Mis- 

 sissippi Valley Historical Association, Vol. 

 Ill, 1909-1910, pp. 159-184. 



The Colonization of the West, 1820-1830, in The 

 American Historical Review, Vol. XI, No. 2, 

 January, 1906, pp. 303-327. 



The Rise of the New West. (The American Na- 

 tion, Vol. XIV), Chapters V, VI, VIII. 



19. Van der Zee, J. The Opening of the Des Moines 



Valley to Settlement, in the Iowa Journal of 



History and Politics, Vol. XIV, pp. 479-558. 

 The Hollanders of Iowa. The State Historical 



Society of Iowa, 1912. 

 The Coming of the Hollanders to Iowa, in The 



Iowa Journal of History and Politics, Vol. 



IX, pp. 528-574. 



20. Statistical Atlas of the United States (1914), pp. 



13-19 for distribution of population by decen- 

 40 



