214 E. C. ANDREWS. 



the general plane of the descending stream, because the 

 percentage of stream energy expended as corrasion is 

 reduced in proportion to the steepness of the declivity. 

 The cirque profile immediately above the basin or flattish 

 floor arises as a compromise between the forces of sapping 

 and the action of the descending stream. The uppermost 

 portion, as the factor of stream weight diminishes, will 

 represent the atmospheric slope of repose mainly and will 

 have a less pronounced slope than that of the central 

 portion. 



We do not here insist that the forms which are peculiar 

 to regions of former glacial intensity are the results of 

 glacial corrasion and that the present-day glaciers must 

 stagnate along such channels, but this we do insist on : — 

 Grant that glaciers can corrade rock structures ; grant also 

 a period, or periods, of glacial action which has, or have 

 been, productive of much more intense action than the 

 glaciers of the present time; and that such intense action 

 has only just departed, then the present-day glaciers must 

 appear to stagnate at just those points where the greatest 

 activity of glaciers is demanded by the hypothesis of lake 

 basin origin or " valley deepening " by glacial corrasion. 



The first part of this series is devoted to a discussion of 

 the general stream. Part (2) deals with an application of 

 these principles to ice-action, while in Part (3) applications 

 of stream principles are made to specific areas where 

 deglaciated valleys occur in great abundance. 



The writer especially desires to record his thanks to Dr. 

 G. K. Gilbert through whose kindness and in whose company 

 he was enabled to spend some five weeks in the Calif ornian 

 Sierras during the summer of 1908. Owing also to Dr. 

 Gilbert's friendly criticism of the writer's glacial note of 

 1907, the present simple proof — drawn from mechanical 

 and comparative sources — has been attempted of the con- 



