John F. Baddeley, Russia, Mongolia, and China (2 vols.; London: Macmillan & Co., 1919), I, lxix, lxxiii; Robert J.Kerner, The Urge to the Sea: The Course of Russian History (Berkeley and Los Angeles, Calif.: University of California Press, 1946), pp.66-88; Raymond H.Fischer, The Russian Fur Trade, 1550-1700 (Berkeley and Los Angeles, Calif.: University of California Press, 1943).
