STRIKE FIORDS 157 



There are also valleys which are now free, or nearly free, 

 from ice, and which were filled with ice only in the 

 presence of the great glacier, and these have less charac- 

 teristic glacial forms. It would seem that the presence 

 of the great glacier in Lynn Canal gave them so high a 

 base-level that their ice streams were sluggish and had 

 little power of erosion. 



The valley of Davidson Glacier deserves special men- 

 tion as an illustration of the broad contrast which may 

 exist between the systems of currents associated with 

 different stages of glaciation in the same district. The 

 neves supplying the glacier are not in sight from Lynn 

 Canal, but lie back of the first line of summits, and the ice 

 river flows eastward through a lateral or transverse valley, 

 entering the great fiord approximately at right angles. 

 During the great ice flood the general direction of move- 

 ment was toward the south, and Davidson Glacier did not 

 exist; its valley was not only filled with ice but over- 

 ridden. It results that the upland bordering the Davidson 

 trough in the vicinity of the Lynn trough, is planed and 

 fluted with lines trending southward, while the Davidson 

 trough, being shaped wholly by the Davidson Glacier dur- 

 ing epochs of moderate ice supply, has an entirely inde- 

 pendent sculpture, the lines of which are transverse to 

 those of the overlooking upland. The Davidson trough 

 is a fine example of its type. So far as visible from the 

 sea, it is of uniform width; its parallel walls sweep in a 

 simple curve of large radius and are steep. Although 

 the topography just above and back of them is varied, they 

 themselves have neither salient nor reentrant angles. The 

 glacier has evidently adjusted its channel quite com- 

 pletely to the conditions of its flow, and has at the same 

 time sunk itself deeply into the mountain it traverses 

 (see fig. 2). 



The transverse troughs of the mainland we did not 



