Alfred Hettner, Die Geographie des Menschen, pp. 409-410 in Geographische Zeitschrift, Vol. XIII, No. 8. Leipzig, 1907.
S.B. Boulton, The Russian Empire, pp. 60-64. London, 1882.
E.C. Semple, The Anglo-Saxons of the Kentucky Mountains, The Geographical Journal, Vol. XVII, No. 6, pp. 588-623. London, 1901.
E.C. Semple, American History and its Geographic Conditions, pp. 25-31. Boston, 1903. The Influence of Geographic Environment on the Lower St. Lawrence, Bull. Amer. Geog. Society, Vol. XXXVI, p. 449-466. New York, 1904.
A.R. Colquhoun, Africander Land, pp. 200-201. New York, 1906.
Ibid., pp. 140-145. James Bryce, Impressions of South Africa, p. 398. New York, 1897.