During the milder interglacial period some southern types, such as Rhododendron ponticum, still held their own, but ultimately succumbed.
When the warmer interglacial periods recurred the polar and continental ice-caps melted and the sea-level became raised again - that is, there was submergence of the eroded plateaux formed as indicated above.
The complexity of the glacial period and its subdivision into several glacial epochs, separated by interglacial epochs of considerable length (certainly longer than the postglacial epoch) has a structural consequence in the superposition of successive till sheets, alternating with non-glacial deposits, and also a physiographic consequence in the very different amount of normal postglacial erosion suffered by the different parts of the glacial deposits.
Four defined zones of interglacial deposits are detected, all of which are thought to represent great recessions of the ice, or perhaps its entire disappearance.
The climate of some of the interglacial epochs was at least as warm as that of the present time in the same regions.