PLEISTOCENE SEA-LEVEL 163 



ished. While I do not regard this assumption as valid, 1 

 I entertain it for the moment because it gives a minimum 

 estimate of the pressure of the Chatham Strait glacier. 

 If the then sea plane had the same height as the present, 

 the pressure of the glacier would be modified, by assump- 

 tion, by the sustaining power of 2,900 feet of sea water. 

 This sustaining power is equivalent to about 3,300 feet 

 of the total ice thickness, leaving 2,700 feet of ice to press 

 upon the bottom of the strait; and such a pressure would 

 manifestly be ample for the work of erosion. So far as 

 our numerical data go, this locality affords an extreme 

 case; and as the hypothesis of glacial erosion below 

 present sea-level is not barred for this locality, it is prob- 

 ably not barred for the whole district. 



Another consideration is connected with the reaction 

 of the ocean on the front of the glacier. My own obser- 

 vations, though comparatively limited, are so accordant 

 with Dawson's generalization that I accept with confi- 

 dence his conclusion that the Pleistocene ice front lay 

 outside the present coast line throughout practically the 

 whole district. If the ocean had then its present level, it 

 washed the ice front for hundreds of miles. The power 

 of the ocean to waste a glacier by melting is ordinarily 

 greater than the power of atmospheric agents, and along 

 the present coast of Alaska is much greater. As the fac- 

 tors are complex, it would be difficult to give an analytic 

 demonstration of this proposition, but it is easy to illus- 

 trate by an example. The great confluent glacier which 

 filled Glacier Bay in the eighteenth century had a general 

 depth of 1,000 to 2,000 feet along the axis of the bay, and 

 rested with less depth on adjacent tracts of land. All 

 through the nineteenth century it was depleted, its wast- 

 ing being brought about partly by the sea and partly by 

 atmospheric agencies. The sea not only melted back the 



1 See discussion in chapter in. 



