36 TARR AND MARTIN CHANGES OF LEVEL IN YAKUTAT REGION 



weakest or exposure to wave cutting was greatest. On the promontories 

 they usually form flat-topped benches, and along straight reaches of 

 rocky coast angular notches planed in. the rocks, frequently with uncon- 

 sumed reefs and stacks on the outer margin. These benches (see plate 13, 

 figure 1) often form an opportunity for travel along the coast in places 

 where at the present stand of the sea it is impossible to even land from a 

 boat. In fact, along the present coast many of the headlands rising out 

 of deep water have been so slightly affected by the waves during the brief 

 period since the uplift that even the glacial scratches and polishing have 

 not been removed by the waves, and can be actually traced continuously 

 from above high tide down to and beneath the low-tide mark. 



Where the uplift has been slight — that is, not over a foot or two — it is 

 often difficult to distinguish the older benches from those now forming, 

 since they merge into one another; but in most of the fiord the benches 

 are so clear cut, and so elevated, that from these alone one could be certain 

 of the presence of an upraised strand. 



Naturally we considered the possibility of other explanations, such as 

 glacial marginal channels and the action of iceberg waves at a time when 

 tidal glaciers extended farther down the fiord ; but it required only a little 

 observation to disprove these hypotheses in most places. The widespread 

 and uniform character of the phenomenon, and the almost universal asso- 

 ciation of barnacles and other marine organisms, still clinging to the 

 rock on the benches, sufficed to effectively dispose of other explanations 

 than uplift. 



In two or three places, notably near the Hubbard and Nunatak glaciers, 

 there is evidence of wave cutting at a higher level than at present, appar- 

 ently performed when the ice-fronts were nearer these shores and the 

 waves generated by calving of icebergs more effective. Such shorelines 

 are not more than two or three feet higher than normal, and are not to be 

 confused with the well defined elevated shorelines, which in reality attain 

 their best development not near, but at a distance from, the tidal glaciers. 



ELEVATED SEA CAVES AND CHASMS 



Some of the rocks of the Yakutat series, especially the thin bedded 

 black shales and sandstones, yield more readily to wave attack than others, 

 such as the indurated tuff and massive conglomerate. Accordingly the 

 shores of the inlet furnisli many instances of sea caves and chasms; 

 but in those parts of the coast where the wave-cut benches are elevated 

 these phenomena are found in association with the uplifted shoreline and 

 not with the present stand of the sea (see plate 13, figure 2). The caves 



