part 1] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxxiii 



recognized also in parts of the Antarctic ; in East Greenland ; and 

 even, on a small scale, in the little glaciers of the Alps. During the 

 quiet periods the glacier is said to be ' dead,' as its motion is so 

 slow as to he almost impercepible ; crevasses disappear; it 'melts as 

 it stands'; and its surface becomes littered with, and even buried 

 under, the solid detritus which it contained. During the active 

 intervals the ice starts forward, and is 'alive' again; and, once 

 started, proceeds with gathered momentum, bursting onward like a 

 slow avalanche, tearing itself into a maze of impassable crevasses, 

 and at its termination lurching irresistibly beyond its former 

 bounds. These revolutionary conditions were magnificently dis- 

 played in Alaska some years ago by many of the glaciers, and on 

 the grandest scale by the Malaspina Glacier. In that region 

 Prof. R. S. Tarr & Prof. L. Martin sought to explain the activity 

 as the after-result of the earthquake of 1899, in shaking down 

 avalanches of snow into the neve-basins feeding the glaciers. But 

 this explanation does not appear to be applicable to cases in Spits- 

 bergen and elsewhere, which are equally striking ; and, although an 

 earthquake may be a contributory cause, it has not been proved to 

 be essential. In Spitsbergen in 1910 we saw two glaciers which 

 became confluent before reaching their termination in the sea in 

 the North Branch of Ice Fiord, and one of these, the Svea Glacier, 

 was in the ' dead ' state, while the other, the Wahlenberg, was very 

 much '• alive '. Prof. De Geer has traced the history of these irregular 

 movements in several Spitsbergen glaciers ; and, in describing them 

 to us personally during our visit to Spitsbergen, he put forward the 

 suggestion that they may be due to the inadequacy of the snowfall 

 to maintain a constant flow, so that the accumulated load of several 

 years may be required to overcome the inertia of a quiescent 

 glacier; with the consequence that, once the movement is started, it 

 may go on quickly until the extra load is discharged and a stage of 

 quiescence again reached. If this should prove to be a general cause, 

 it will apply with especial weight to glaciers and ice-sheets accu- 

 mulated on flat ground, or in basins of gentle gradient; and I think 

 that it may enable us to comprehend many peculiarities of our 

 drifts. Particularly, it will explain the common occurrence of level 

 tracts of boulder-clay at the surface over wide areas. I have often 

 striven to understand how these broad surfaces could be left by a 

 retiring glacier without any covering of fluvio- glacial material; my 

 difficulty being that, whereas the ice in liquef} r ing must every- 

 where have set free great floods of water, which should have caused 



