GLACIATION OF AN ICELANDIC VALLEY 133 



To sum up the glacial history of the valley; it is evident that, 

 during the formation of the Tertiary basaltic plateau, there were 

 several advances of a glacier. This glaciation was probably local 

 rather than continental, as the indurated ground-moraines are not 

 a common feature of the plateau. After the break-up of the plateau — 

 and the isolation of Iceland — by faulting — the evidence goes to show 

 that the region was again glaciated by an ice-cap, moving radially 

 outward from the center of the island. This is suggested by the 

 directions of ice-movement, given by professor Thoroddsen in 

 his geological map of Iceland,' and by the direction of strias on the 

 Botnsheidi and the faint stria of S. 15° W. direction found on the 

 basalt under the pleistocene volcano. The ice-cap gradually retreated 

 and became broken up, the remnant, sending down glacier tongues 

 which eroded out the valleys, as is the case today with the Vatna, 

 Myrdals, Eyafjalla, Lang, Dranga, and other great ice-fields of the 

 island. During the period of valley glaciation, and after the excava- 

 tion of the valley, a small volcano, possibly contemporaneous with Mos- 

 fell, a pleistocene volcano, 20 miles to the southeast, broke out under 

 the ice, causing sudden floods, which have left their characteristic 

 deposits. The glacier, however, recovered what was lost by this melt- 

 ing, as is shown by the indurated moraine above the glacial volcano, 

 and in one of its recent stages advanced to the shores of the Hvalfjord 

 and there deposited its best-marked terminal moraine. On the last 

 retreat of the ice, this moraine probably formed a dam holding back 

 the waters of a glacial lake. The sea, being nearly at the top of the 

 moraine, prevented the drainage of the lake, until the uplifting of 

 the land allowed the stream to cut through the morainal barrier; 

 or else the sea- water of the fiord itself followed the ice on its retreat 

 and the delta was deposited at the head of a former extension of the 

 Hvalfjord. 



'See also Th. Thoj-oddsen "Explorations in Iceland during the Years 1891-98," 

 Geographical Journal, Vol. XIII (1899), No. 5, p. 493. 



