CERTAIN PHASES OF GLACIAL EROSION 199 



to year, comes to take on motion as a glacial body, the erosion to 

 which its motion gives rise must take a form coincident with the 

 moving part of the snow-ice mass. The erosion is assumed to 

 be due to the adhesion of the snow-ice mass to the ground on which 

 it rests — to the soil and loose rock at the start, to the progressively 

 loosened and ground rock below later. A broad patch of soil and 

 loose rock coincident in form with the moving part of the snow 

 mass is first dragged away and the configuration of the scar is 

 distinctive of the action. If erosion beneath the moving glacier 

 mass continues the excavation will in time come to have the form 

 shown in Fig. 3. Such excavations are to be looked upon as 

 embryo cirques. They are found on the lee crests, brows, and 

 slopes of round-topped mountains known to have been subjected 

 to local glaciation. Less typical initial cirques are formed in 

 ravines where snow lodgment gives rise to glaciers. 



If absolute certainty that there has never been any previous 

 glacial action in a given region is regarded as a prerequisite to 

 an irreproachable illustration of this class of actions, such a case 

 is difficult to demonstrate because the configurations left by the 

 older glaciations have often been so largely lost in the subsequent 

 sculpturing of the common wear-and-weather type that the absence 

 of previous glacial work is hard to prove in regions likely to have 

 been glaciated recently, but this is only a question between the 

 work of different glacial stages, not between glacial and aqueous 

 methods. But though a region has been subjected to previous 

 general glaciation, even rather recently, geologically speaking, the 

 typical effects of local glaciation on rounded ' contours are dis- 

 cernible much as in wholly unglaciated regions, for the con- 

 tours shaped by the general ice movement conform to the domi- 

 nant horizontality or the low inclination of such general ice move- 

 ments, while the lines of local ice movement are decisively down- 

 ward in conformity to the local slope. 



These considerations are here put in the theoretical form, but they 

 suggested themselves almost as inductions during a summer trip 

 along the coast of Norway in 1909. They arose naturally from the 

 abundant and instructive phenomena of that region, where former 

 glacial action merges into present action. The configurations 



