FEATURES OF VALLEY GLACIER EROSION 721 



sides; (e) alignment and straightening of valley sides by truncation and 

 removal of projecting and overlapping spurs; (/) valley sides, occasion- 

 ally terminating in vertical cliffs; (g) absence of tains slopes at base of 

 cliffs; (h) flat open valley floors now usually covered with debris, left by 

 receding glaciers and worked over to some extent, at least, by subsequent 

 stream action. Occasionally low rounded knobs of bedrock project above 

 the valley bottom, but are not of sufficient size or frequency to disturb 

 its general aspect. 



FEATURES DEVELOPED AT JUNCTIONS OF TRIBUTARY GLACIERS WITH 



TRUNK GLACIER 



Hanging valleys. — At the points of confluence of tributary valleys 

 with the main valley, different physiographic effects occur, dependent on 

 the relative size of the two valleys and on their angle of confluence. 

 Small ice-tongues, entering the main valley at large angles, were under- 

 cut by the master ice-stream, which left their valley floors perched or 

 hanging at different elevations along the sides of the main valley; water- 

 falls emphasize still further the sites of such hanging valleys, and are so 

 plentiful in Iceland that the traveler is rarely out of sight of one or 

 more; in most cases water erosion at such points has been slight, and 

 small notches only have been cut in the lips of hanging valleys since the 

 recession of the ice. 



Glacier junction 'basins. — Larger ice-streams, confluent at wide angles 

 and yet able, practically, to hold their grade with that of the trunk 

 glacier, tended to widen and overdeepen the main valley at the point of 

 union ; there the valley grade was frequently reversed for a short distance 

 with resultant formation of rock basins, now filled with glacial material. 

 When several such converging valleys entered the main valley on oppo- 

 site sides, a wide, open amphitheater was formed, which for impressive- 

 ness and dignity far surpasses any feature of ordinary river valleys. 

 Eyjafjardardalur is especially noteworthy because of such valley junc- 

 tions. 



Glacier junction spurs. — In the case of two large glacial valleys con- 

 fluent at acute angles, characteristic, low junction spurs, attenuated by 

 the overriding ice-masses to elongated shapes, rounded in cross-section 

 and almost cigar-shaped in plan, were usually formed. These glacier 

 junction spurs, as they may be called, are a distinctive feature of certain 

 glacial valleys and merit a brief word of description. The normal ten- 

 dency of intense glacial cutting in valleys is to truncate and even to 

 remove all projecting spurs which lie in the path of the advancing ice- 

 flow and to align their bases. In the case of glacier junction spurs, how- 



