For a long time it has been supposed that the glacial deposits of the central regions of Russia were accumulated during the advance and retreat of one and the same ice-sheet. In 1888, however, Professor Pavlow brought forward evidence to show that the province of Nijnii Novgorod had been twice invaded by a general _mer de glace_. During the first epoch of glaciation the ice-sheet overflowed the whole province, while only the northern half of the same region was covered by the _mer de glace_ of the second invasion. Again, Professor Armachevsky has pointed out that in the province of Tchernigow two types of glacial deposits appear, so unlike in character and so differently distributed that they can hardly be the products of one and the same ice-sheet. But until recently no interglacial deposits had been detected, and the observations just referred to failed, therefore, to make much impression. The missing link in the material evidence has now happily been supplied by M. Krischtafowitsch.[CF] At Troïzkoje, in the neighbourhood of Moscow, occur certain lacustrine formations which have been long known to Russian geologists. These have been variously assigned to Tertiary, lower glacial, post-glacial, and pre-glacial horizons. They are now proved, however, to be of interglacial age, for they rest upon and are covered by glacial accumulations. Amongst their organic remains are oak (_Quercus pedunculata_), alder (_Alnus glutinosa_, _A. incana_), white birch, hazel, Norway maple (_Acer platanoides_), Scots fir, willow, water-lilies (_Nuphar_, _Nymphæa_), mammoth, pike, perch, _Anadonta_, wing-cases of beetles, etc. The character of the plants shows that the climate of central Russia was milder and more humid than it is to-day. [CF] _Bull. de la Soc. Impér. des Naturalistes de Moskau_, No. 4, 1890.