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and had crowded out over a rock gorge, destroying the 

 glacial stream that had occupied it in 1905. 



It was evident from these facts that the glaciers in 

 question had been subjected to some unusual impulse that 

 had caused a sudden forward rush, which had pushed them 

 forward, thickened them and greatly broken their surfaces. 

 In seeking an explanation for such a phenomenon, not 

 hitherto recorded, but one cause seemed adequate, namely, 

 the severe earthquake shocks to which this region was 

 subjected in 1899. Tarr advanced the hypothesis that 

 the repeated violent shaking during the earthquakes that 

 occurred between September 3 and 29 threw down so much 

 snow into the reservoirs of the glaciers, that a wave of 

 motion was started which reached completely down to the 

 terminus of Galiano glacier some years before 1905, and 

 which was passing down the four other glaciers during 

 1906. In testing this hypothesis with the facts available, 

 all were found to be in harmony with it, none were dis- 

 covered that were opposed to it, and no other hypothesis 

 could be suggested which had no facts fatal to it. 



While, therefore, the hypothesis of earthquake cause 

 for this advance seemed well supported, it was desired to 

 subject it to still further test, and one of the main objects 

 of the work in 1909 and 1910 was to apply these tests. 

 There were three such tests which Tarr and Martin had 

 especially in mind. In the first place, if the advance were 

 due to this cause, it should be confined to the general region 

 of violent earthquake shaking. By inquiring about the 

 condition of glaciers southeast of Yakutat bay, and by 

 studying some of the glaciers of the Prince William Sound 

 region to the northwest, they were able to apply this test 

 to some extent, but not fully enough to warrant a definite 

 statement of its adequacy in support of the hypothesis. 



The second test is the behaviour of other glaciers in 

 the Yakutat Bay region in the years since 1906. If the 

 hypothesis were correct, probably some of the smaller 

 glaciers of Yakutat bay had advanced before 1905, and 

 certainly some of the other glaciers of the region ought to 

 show signs of the wave of advance. This was predicted 

 by Tarr [72] in 1906. There is reason to believe that there 

 was an advance of some of the smaller glaciers before 1905, 

 though it is now difficult to obtain convincing evidence, 

 but that the wave of advance had extended to other glaciers 

 between 1905 and 1909 was strikingly illustrated by Hidden 

 glacier [75], which had advanced two miles (3.2 km.) and 



