POLLEN- ANALYTICAL STUDIES 357 



this interval appears a great maximum of Sphagnum, a plant which today is 

 not spore-producing in Iceland. 



C. This Betula-minimnm is thereafter followed by a second great Betiila- 

 maximum which corresponds to the Sub-Boreal and the lower part of the 

 Sub-Atlantic periods. In this pollen zone, most probably in the interval 4000- 

 2500 B.P., falls the Hypsithermal period in Iceland. At this time at least 50 

 per cent of Iceland was covered with birch forest as contrasted to 1 per cent in 

 modern times. Within this pollen zone occur two rhyohthic tephra (volcanic 

 ash) layers from Hekla, H4 (4000 B.P.) and H5 (2700 B.P.). 



The numerous, partly C^^-dated, tephra layers in the Icelandic peat 

 deposits greatly aid pollen analytical work. The tephra layers have been 

 thoroughly studied by Thorarinsson (1944, 1954, 1958) and facilitate the 

 geological work in Holocene deposits. They are also of great importance for 

 the study of the volcanic history of Iceland in Post-Glacial times. 



Another feature that can be seen from the tephra layers is that the pre- 

 historic ones are straight and even in the bog profiles, in contrast to the 

 historic ones which are uneven and lenticular. This deformation of the 

 historic tephra layers is probably a result of the beginning of the cryoturbant 

 "thufur"-(hillock)-formation in Iceland in the last thousand years. The 

 "thufur"-formation could indicate a climatic deterioration in historic times or 

 be the result of deforestation. In places where forest and/or shrub cover is 

 lacking snow is blown away by wind. Absence of the insulating snow cover 

 thus results in a much more effective frost action in deforested areas. 



The Betula-cmwQ thereafter decreases generally with some local deviations 

 from 2500 B.P. to the time of settlement (ninth century a.d.) in accordance with 

 the climatic deterioration at the beginning of the Sub-Atlantic period. At the 

 beginning of pollen zone D, historic times, the Betiila-curwQ decreases very 

 rapidly and the Gramineae-curve rises, indicating the influence of man. 



In pollen diagram 2 from Sogamyri, Reykjavik, southwestern Iceland 

 (Fig. 2), the pollen zone A is Betula-free. This suggests that the Betula was 

 growing for a much longer time in northern Iceland east of the Eyjafjordur 

 mountains to the Austfjordur mountains. Perhaps it has survived there on 

 ice-free areas in the mountains and /or on a dry coastal shelf during the last 

 Glacial, as this interpretation of the pollen diagrams seems to indicate. 



As has been mentioned in other lectures in this symposium, the Early 

 Tertiary flora of Iceland was characterized mainly by deciduous-trees 

 whereas the Late Tertiary was dominated by conifers (Pflug, 1959). With the 

 setting in of the Pleistocene Glacials the heat-demanding trees were eliminated 

 and only species of A hms, Betula, and Salix survived the First Glacial. In the 

 second to last Glacial Alnus, too, disappeared from the flora. 



Kjartansson (1955, 1961) has shown, through studies on Glacial striae, 

 that the ice-divide in late stages of the retreat of the ice-sheet in the Last 

 Glacial was near the Torfajokull-area, i.e. more than 50 km south of the 



2A 



