216 THORODDSEN 



have been produced before the surface assumed its present form, 

 others have been formed after the country had in all essentials 



, 



acquired the sculpture it has to-day; several of them have flowed 

 down through valleys and hollows. Reykjavik is built upon such 

 a doleritic lava-stream, and there the dolerite is much used for 

 building purposes. In several places the glacial lavas are of con- 

 siderable thickness (100 200 metres and more). Some larger vol- 

 canoes, which have been in eruption as late as within historic times 

 (Eyjafjallajokull, Snsefellsjokull, Oraefajokull), began their activity 

 even during the Glacial period and at that time discharged doleritic 

 lava-streams. In several places in West and South Iceland large 

 deposits of conglomerates occur, with rolled gravel and sand, alter- 

 nating now and then with moraine material and ice-striated lavas; 

 these resemble the "Nagelfluh" of the Alps and were perhaps formed 

 in a similar manner. 



During the Glacial period the whole island \vas wrapped in a 

 sheet of inland-ice through \yhich only a few small peaks projected 

 here and there near the edges. The Jokulls (sno\v-fields) of the 

 mainland probably extended on all sides down to the sea, for the 

 bottom-moraines of that time are found everywhere, both on the 

 plateau and in the lowlands; the lateral and terminal moraines 

 which occur in the valleys and lowlands, date from a later period 

 when the ice was retiring; it appears also that large masses of 

 moraine-material occur here and there on the sea-bottom off the 

 mouths of the fjords. The north-western peninsula was probably 

 covered with a separate ice -sheet, from which numerous small 

 glaciers, with intervening ridges free from ice, descended to the sea. 

 The ice-sheet of the Glacial period had, on the interior plateau, a 

 thickness of 700800 metres. Ice-striated rocks occur all over the 

 island, both in the high land, in the valleys, and in the lowlands, 

 as also on islands and skerries. Large and small erratic blocks are 

 found in thousands scattered over the whole of Iceland. 



As mentioned above, it is assumed that Iceland, in the begin- 

 ning of Tertiary times, was connected by a broad land-bridge 

 with Greenland, the Faeroes and Scotland; this land-bridge was a 

 volcanic highland or plateau-land formed by innumerable lava- 

 streams which originated principally from rows of craters and from 

 fissures. The plateau, which had a height of 3000 4000 metres 

 above sea-level, w r as towards the end of the Miocene period broken 

 up and depressed; by this subsidence, perhaps in conjunction with 



