132 



HENRY G. FERGUSON 



shown in Fig. lo a stream-bed has been filled with an angular imstra- 

 tified volcanic breccia. These sediments rest on glaciated "regional" 

 basalt which shows the same double set of striations as before. 



Later glaciation of the valley is shown by recent polishing of rock- 

 ledges, the striations running parallel to the direction of the valley, 

 and by three well-marked frontal moraines. The westermost of 

 these, at an altitude of about 150 feet, forms a barrier across the 

 valley, except where cut through by the present stream; the other 

 two are merely remnants on the sides of the valley. At the north- 

 ern end of the valley is a large delta, perhaps 1 50 feet above sea-level, 

 somewhat over a mile in length, which marks the head of a body of 



mmm^^^^^ 



I ft 







^r^rg^ 



UO^ 





o - . - <_i . - 



c 



Fig. 10. — " J5kullhlaup " sediments and volcanic breccia. 

 a, volcanic breccia; &, roughly cross-bedded sandstone; c, conglomeratic sandstone; rf, glaciated 

 basalt. 



water formed after the retreat of the last valley glacier. If this were 

 a fresh-water lake, it is remarkable that its level remained constant 

 long enough to allow such a large delta to be built, if the outlet 

 stream was at a grade to enable it to do any effective down-cutting 

 on the morainal barrier. The possible explanations seem to be either 

 that, at the time of the formation of the delta, the sea stood at, or 

 nearly at, the height of the top of the moraine, and that the gradual 

 uplifting of the land allowed the stream to cut through the morainal 

 dam and so drain the lake, or that the fiord itself formerly ex- 

 tended to the delta, and that the moraine was deposited in its shallow 

 waters. These inferences are rendered more probable by the presence 

 of old beaches and shell-beds at many places along the whole coast of 

 Iceland, at elevations of from 50 to 300 feet above the present sea- 

 level. 



