PRESSURE OF TIDAL GLACIERS 217 



tidal glacier has been greatly overrated, and I discredit 

 the supposed power of sea pressure to make important 

 reduction of a glacier's efficiency for erosion. 



The preceding pages were submitted in manuscript to 

 several friends competent to consider questions in molec- 

 ular physics. Some of them think the ability of the sub- 

 glacial film to resist expulsion has been overestimated, and 

 especially that the film should not be assumed to exist 

 between the bed-rock and the abrading angles of rock 

 particles held in the ice. If it be true that abrading par- 

 ticles are in absolute contact with the bed, and if it 

 be further true that there is no film between the same 

 particles and the partly enveloping ice, then parts of the 

 glacier (regarded as a body of ice and fragmental rock) 

 are directly supported by the bed. However important 

 the distinction may be with reference to a complete 

 theory of glacial abrasion, it seems to have little bearing 

 on the question of pressure as here considered. We 

 may conceive the whole glacier to consist of infinitesimal 

 vertical columns, some terminating on the bed and sup- 

 ported by it, others resting directly on a capillary film of 

 water and thus indirectly supported by the bed, and yet 

 others terminating on a water stratum of supercapillary 

 depth. The last are sustained in part only by the hydro- 

 static pressure communicated by the water stratum, and 

 are otherwise upheld directly by their coherent neighbors 

 of the first and second groups, and through them, indi- 

 rectly, by the bed. 



It is a corollary to the general conclusion of this section 

 that the existence of a fiord that is, of a glacial trough 

 partly occupied by an arm of the sea is not demonstra- 

 tive of a relatively low base-level at the time of its excava- 

 tion. In the regions of the Alexander Archipelago and 

 Prince William Sound there is independent reason to 

 think the base-level was relatively low when the glaciers 



