There is one deposit which is of considerable importance in the study of interglacial climates, and that is the loess. Loess is an exceedingly fine-grained homogeneous deposit resulting from the gradual accumulation of wind-blown dust on a surface sparsely covered with vegetation. It is to be seen accumulating at the present day in parts of south-east Russia and central Asia. Its formation, except in closed basins, needs a climate of the steppe character, with not much rainfall, and especially with a long dry season. Now loess was very extensively developed in Europe during the Quaternary. Its occurrence is peculiar, since it is found most widely developed resting on the deposits of the Rissian glaciation, and is never found resting on the moraines of the Wurm glaciation. A little loess is found below the Riss moraines, and it has also been found between the Riss and Wurm moraines. In the pre-Rissian loess an implement of Acheulian age was discovered in 1910 at Achenheim (Alsace), by R. R. Schmidt and P. Wernert, indicating that the deposit was formed towards the close of the Chellean industry, when the climate was already cold and dry. In the same section the younger loess seems to fill completely the Riss-Wurm interglacial, since Mousterian implements were found at the base and Aurignacian implements in the middle. The younger loess contains remains of the jerboa and other rodents at present inhabiting the Siberian steppes. It is therefore reasonable to conclude that steppe conditions prevailed in central Europe through practically the whole of the Riss-Wurm interglacial, and the same probably applies to the corresponding pre-Wisconsin interglacial in America. But if a steppe climate prevailed in central Germany there must have been very severe conditions in Scandinavia, and probably the ice-sheet maintained a quite considerable area there throughout the whole period, though without encroaching on the Baltic basin. In North America the loess was deposited by westerly winds, indicating that the ice-development was not sufficient to impose anticyclonic conditions in place of the present prevailing westerly winds, and the same appears to be true of Europe. Similar climatic conditions were developed for a short time at the close of the Wurm glaciation, but without any appreciable development of loess. (See Chapter XIII.) BIBLIOGRAPHY Wright, W. B. “The Quaternary Ice-age.” London, Macmillan, 1914. Brooks, C. E. P. “The correlation of the Quaternary deposits of the British Isles with those of the continent of Europe.” _Ann. Rep. Smithsonian Inst._, 1917, pp. 277-375. de Geer, G. “A thermographical record of the late Quaternary climate.” _Ber. Internat. Geologenkongr._, Stockholm, 1910. “_Die Veränderungen des Klimas_,” p. 303. ——. “A geochronology of the last 12,000 years.” _Ber. Internat. Geologenkongr._, Stockholm, 1910, Vol. 1, p. 241.