PHYSICAL GEOGRAPHY 219 



observed affording evidence of an upheaval of the land in our own 

 day. Shortly after the Glacial period the climate was somewhat 

 milder than it is now; in northern Iceland abundance of Pnrpnra 

 lapillus has been found in shell-mounds, and this still lives in the 

 sea south of Iceland, but not in the colder water along the north 

 coast. In bogs on the northernmost headlands, \vhere birch woods 

 no longer thrive, remains of Betula alba are found, while Betnla 

 verrucosa, which no longer grows in Iceland, has been found in 

 the bogs of South Iceland. 



Volcanoes and Lava-streams. Iceland is one of the most 

 volcanic countries in the world; as mentioned above, the island 

 throughout has been built up by volcanic activity which began 

 early in Tertiary times and has continued to the present day. 

 There are records to hand of 138 eruptions from 30 volcanoes within 

 historic times, but many eruptions undoubtedly took place in early 

 times which either were not recorded or occurred in the inland 

 wastes and snow-fields without being noticed by the inhabitants. 

 At the present time. 130 post-Glacial volcanoes are known in Iceland, 

 and several volcanic vents have undoubtedlv still to be found, or 



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else have been effaced or destroyed by erosion. All the numerous 

 volcanoes have, in the course of time, since the Glacial period, dis- 

 charged enormous quantities of lava, and the post-Glacial lava-fields 

 of Iceland cover an area of about 11200 square km.; they occur 

 over the country in vast expanses around the volcanoes from 

 which they have originated. The majority of these lava-fields have 

 been produced not by one but by numerous eruptions at various 

 times, and the greater part of the lava dates from pre-historic out- 

 bursts. The largest lava-stream which has been poured forth during 

 a single eruption within historic times, is that which issued from 

 the craters of Laki a row of craters formed in 1783; this stream 

 covers an area of 565 square km.; and its mass occupies about 

 12Vs cubic kilometres; it is probably the largest lava-stream upon 

 the surface of the earth which, within historic times, has been 

 known to flow out during a single eruption. The largest continuous 

 lava-field in Iceland is OdaSahraun on the plateau north of Vatna- 

 jokull (600 1200 metres above sea-level); it was produced by nu- 

 merous eruptions from more than 20 volcanoes, and covers an area 

 of about 4000 square km. The lava-field, next in size, which origi- 

 nated from the many large craters near Vei5ivotn, west of Vatna- 



15 



