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 
