H.J. Mackinder, Britain and the British Seas, pp. 198-199. London, 1904.

John Richard Green, The Making of England, Vol. I, pp. 63, 66. London, 1904.

J. Partsch, Central Europe, p. 102. London, 1903.

Miller and Skertchley, The Fenland Past and Present, pp. 10, 11, 27-30. London, 1878.

W.Z. Ripley, Races of Europe, pp. 322-323. Map p. 327. New York, 1899.

Anatole Leroy-Beaulieu, The Empire of the Tsars, Vol. I, p. 108. New York, 1893.

Ibid., pp. 104-106. W.Z. Ripley, Races of Europe, pp. 340-342, 352, 365. New York, 1899.

J. Partsch, Central Europe, p. 135. London, 1903.

Ibid., p. 133. W.Z. Ripley, Races of Europe, pp. 294-295. New York, 1899.

Herodotus, II, 137, 140.