GLACIERS AND RIVERS COMPARED 221 



way that the total work of channel friction and internal 

 shear is a minimum, and that distribution throws the locus 

 of maximum velocity to the outer side of the middle of the 

 stream, but the general relations of the parts of the stream 

 are not changed. The preservation of the general rela- 

 tions is clearly shown by medial moraines, which map out 

 surficial lines of flow. In the bending river, momentum 

 is the controlling factor. Those fillets of the stream which 

 above the bend moved fastest are thrown to the outer side 

 of the curve, and the slower-moving fillets are crowded to 

 the inner side. Usually the upper water moves to the 

 outside of the bend and the lower water to the inside, so 

 that there is a torsion of the body of water as a whole. 



The correspondences connected with gain and loss of 

 material are close, and the parallelism can be traced 

 through many details, but the processes are so different 

 that the similarities of result can not be classed as homol- 

 ogies. Alimentation of the glacier is primarily through 

 snowfall, secondarily through rainfall, and there is storage 

 in snow banks that subsequently descend as avalanches. 

 Alimentation of the river is primarily through rainfall, 

 secondarily through the melting of snow and ice, and 

 there is storage in ground water that slowly issues in 

 springs. Dissipation of the glacier is chiefly by melting 

 and secondarily by evaporation. Dissipation of the river 

 is wholly by evaporation, but part of its evaporation is 

 preceded by absorption by the ground. 



The general evenness of the stream surface is deter- 

 mined in each case by gravity, and so is its descent in the 

 direction of flow; but the exceptional ascent in the direc- 

 tion of flow has diverse causes. Where the passage of 

 an ice stream over an embossment of its bed is expressed 

 by a local rising of its surface, the imperfect adjustment 

 of the surface is a result of viscosity; the upward slope of 

 water under similar circumstances is a result of impetus 



