Even in Iceland there are indications of a dry period following the last glacial maximum, for tree-trunks, buried in the peat-bogs, show that the birch formerly had a much greater extension. It is also quite possible that there was an accentuation of desert conditions in Asia during the retreat of the glaciers in Europe and North America, which may have played a part in the wave of Neolithic migration that appears to have overwhelmed the artistic Palæolithic races of western Europe; but of this we have as yet no direct evidence. The Neolithic invasion of Europe took place along two main routes, the Nordics passing from the centre of Asia north of the Caspian, across Russia to the Baltic shores, where they became the Kitchen-midden people; and the Alpine race passing from Transbaikalia, south of the Caspian and Black Sea, into southern Europe. The Nordics drove before them an older race, characterized by the transitional Maglemose culture, which passed from east of Russia to the shores of the Baltic and ultimately to England, where harpoons of Maglemose type have been found beneath the peat of Holderness. In the southern hemisphere the continental phase does not appear to have been so well developed. The uppermost part of the Pampean loess is possibly post-glacial; more certainly so are the sand-dunes on the coast near Buenos Aires, in which human remains have been found in association with the bones of some extinct animals. In New South Wales, after the retreat of the glaciers, there was a period with land a little above its present level, so that the stools of Eucalyptus trees are now found ten feet below sea-level; but there is no evidence as to the climate of this stage. In New Zealand we have no definite post-glacial beds of continental type. The occurrence of xerophilous plants, such as _Aciphylla_, still living in a climate which is now decidedly moist, may be a remnant of a continental phase in New Zealand, or may date back to the steppe conditions of the loess. As to Antarctica, we have, of course, no evidence. BIBLIOGRAPHY Brooks, C. E. P. “The evolution of climate in north-west Europe.” London, _Q. J. R. Meteor. Soc._, 47, 1921, p. 173. Wright, W. B. “The Quaternary Ice Age.” London, 1914. (Ch. 17, Late-glacial changes of level in North America.) _Bericht Internat. Geologenkongress_, Stockholm, 1910. “Die Veränderungen des Klimas seit der Maximum des letzten Eiszeits.” Numerous papers, dealing with Europe and North America. Munthe, H. “Studies in the Late-Quaternary history of southern Sweden.” Stockholm, _Geol. Foren. i Forh._, 22, 1910, pp. 1197-1292. Antevs, E. On the late-glacial and post-glacial history of the Baltic. _Geogr. Rev._, New York, 12, 1922, p. 521. CHAPTER XIV THE POST-GLACIAL OPTIMUM OF CLIMATE