GLACIATION OF AN ICELANDIC VALLEY 131 



inter-volcanic, as if it was even more thoroughly lithified than the 

 indurated moraines in the Tertiary basalts. The pebbles were of 

 vesicular basalt and, owing to their slaggy nature, did not show 

 as good striations as the Tertiary moraines described above. The 

 pebbles were all subangular, however, and a number showed stria- 

 tions. 



A narrow gorge through this volcanic remnant showed an inter- 

 esting section. The northern side was composed chiefly of tuff, vol- 

 canic breccias, and bomb-breccias, and thin lava flows, overlain by the 

 indurated ground-moraine. These deposits rested on the older 

 "regional" basalt, which showed distinct glacial striations, one 

 rather faint set trenchng S. 15° W., the same direction as on the 



Fig. 9. — Contact of tilted basalts and upper moraine. 



Botnsheidi, the plateau above the valley, showing the existence of 

 an ice-sheet radiating outward from the center of the island; and the 

 other more distinct trending S. 60° W., showing the action of a glacier 

 following the present direction of the valley. The southern side of 

 this hill has suffered most from recent glacial erosion, and here the 

 indurated moraine seems to have been eroded off. Small pieces of 

 a similar indurated moraine are found in the later terminal moraines 

 at the mouth of the valley. The sedimentary beds, however, are 

 different from those seen on the northern side of the hill. These 

 are in part deposits, which Dr. Pjetursson believes to be due to a 

 "jokullhlaup," literally "glacier-run," a flood caused by the sudden 

 melting of vast quantities of ice, by a subglacial volcanic eruption. 

 This material consists of very roughly stratified sandstone and con- 

 glomerate, of rapidly changing texture, varying from a hard clay, 

 which, however, often contains subangular bowlders, to a coarse 

 conglomerate. Often these beds show a faint and rather irregular 

 cross-bedding. Large "scour and fill" unconformities are common, 

 showing frequent changes in the stream-courses. At the point 



