These Notes are printed separately since the text was written to be read continuously and it was not wished to divert the reader's attention by notes at the foot of the page or by numerals pointing to the end of the book. Some of the Notes are simply references to books the use of which it would have been ill-mannered not to acknowledge: others are explanations and, in a few cases, comments, on points where the text may have left a question mark in some readers' minds.
In the brief analysis of Mackinder's ideas and outlook in the text, account has been taken not only of the 1904 lecture but also of his geography lectures at Oxford during the same period, of which the writer has a clear recollection. Much of the substance of these was embodied in a book, Democratic Ideas and Reality, published in 1919 and republished in the United States in 1942. See also the prescient concluding paragraph of Britain and the British Seas, published in 1902. Mackinder's final pronouncement was an article contributed to Foreign Affairs in July, 1943. In this he analyzed the concept of the Heartland in greater detail, describing it as "the greatest natural fortress on earth." He pointed out, that, broadly speaking, the territory of the U.S.S.R. is equivalent to the Heartland, except in one direction. That exception is the rugged forest-clad country, to the East of the grassland zone, extending from the Yenisei River to the Bering Strait. He called this country "Lenaland," drawing attention to the fact that, as contrasted with Heartland Russia, with its more than 170 million inhabitants, it is very sparsely populated and its rich natural resources as yet virtually undeveloped. At the time when Mackinder wrote, the gold-mining industry in the Dalstroy area, with its horrible system of slave labor, was not yet known in the West. See the map on page 65 of Dallin and Nicolaevsky, Forced Labor in Soviet Russia ( Yale University Press, 1947).