Biogeographers and geologists have disagreed about the extent and thickness of the ice shield during the last glacial age in Scandinavia. The relevant plant geographic data have been summarized. Presence of west arctic species otherwise lacking in Europe and western Asia, marked endemism, and the concentration of rare species in two separate areas of the Scandinavian mountains indicate that much of the present arctic-alpine flora has survived the last glacial age in refuges along the Scandinavian coast and adjacent mountains. Fossil records indicate that conditions in South and Central Sweden were not favorable for immigration from the south of much of this flora during the deglaciation period. Other fossil records indicate that arctic-alpine plants grew in the mountains immediately after deglaciation. Current geological methods for recognizing areas left unglaciated during the last glacial age in Scandinavia are considered. Unweathered erratics, glacial striae, etc., do not prove glaciation since they may have been deposited or formed during an earlier glacial age.
Some geologists believe that frost splitting in arctic and high alpine localities is so rapid that glacial striae and erratics could not survive a glacial age in Scandinavia. The rapid frost splitting is thought to be due to frequent shifts of temperature around 0°C or to severe frosts in winter. Available meteorological observations do not confirm that such shifts are any more frequent in arctic or high alpine localities than in the valleys and plains of North Europe. Strong weathering has also been observed in localities with no severe winter frost. In the Peruvian Andes where frequent shifts around 0°C occur, weathering differs from that observed in Scandinavian mountains.
The origin of mountain-top detritus, masses of large boulders weathered out in situ from the underlying rocks, is not completely understood. It probably has formed during a very long weathering cycle.