G. K. Gilbert—The Deflection of Streams. 431 
of magnitude, and may reasonably be expected to modify the 
results of the more powerful agent. In the present state of 
hydraulic science it is impossible to define the quantitative 
relation between the tendency of swift threads of current 
' relation may be, I conceive that rotation is competent to pro- 
duce appreciable results wherever those due to curvature are 
reat. 
(2.) A stream engaged in the deposition of detritus, as on a, 
delta or an alluvial fan, shifts its channel from side to side by 
a process entirely distinct from the one just described. It 
builds up its bed until it is higher than the adjacent plain, and 
then transfers its current bodily to a different course. Rota- 
tion has its share of influence in determining the direction of 
this transfer, and it thereby induces the stream to build its 
alluvial plain higher on the right than on the left; but, the 
difference of level having been established, the stream has 
thereafter no more tendency to one side than the other. Deflec- 
tive effects of rotation are therefore not to be sought in regions 
of alluvial deposition. 
t may be remarked also that the tendency of a stream 
toward one bank or the other by reason of curvature and rota- 
tion is often overpowered by an opposite tendency due to 
obstructions. These include resisting members of the eroded 
terrane and alluvial dams deposited at one bank or the other 
by tributaries. : 
A general curvature in the course of the valley through 
which the stream flows has the same tendency, though in a less 
degree, as does the curvature of a short bend, and this tendency 
must in many instances nullify or conceal the results of rota- 
tion. 
Lewis in this Journal for February, 1877, and which has re- 
. Mr. The 
