VISCOSITY AND MOMENTUM 223 
causeway are made by the deposition of suspended waste 
through the slackening of spreading side currents. 
The salient fact brought out by these comparisons is 
that many features of rivers and river work which arise 
from inertia in association with swift motion are paralleled 
by features of glaciers and glacier work which arise from 
high viscosity in association with slow motion. In each 
kind of stream, changes in the direction of flow are caused 
by irregularities of the channel, and complex series of 
phenomena arise from the resistance of the current to 
deflection. These series are strikingly parallel, but the 
resistance to deflection is occasioned in one case by 
momentum and in the other by viscosity. 
