86 STUDIES FOR STUDENTS 
as for its many admirable expositions of rain and river work,’ 
contains the following account of the problems here considered: 
Suppose a barrier of rock to run across any valley or river bed ; when 
the bed of the valley or river on the upper side of the barrier has been worn 
down to a horizontal level with this barrier, it can zo¢ go lower..... But 
as the barrier is cut through, the bed of the valley or river will be deepened 
backward, or from below upward, or towards the hills... .. The passage 
of the detritus and soil from the inclined upper parts of valleys is checked 
in the horizontal lower parts of valleys, and soil accumulates there. This is 
the origin of alluvial plains; and a river of any size, or any rapidity, may, at 
any distance from the sea, have fazches of alluyial plain, where no lakes 
have ever been; that is, above every rapid or accidental barrier of hard 
grounds. ge The only difference in the laws for the growth and gradient 
of these patches from those which regulate the growth and gradient of the 
plain at the level of the sea, is that they have no zzcreasimg cause for rising 
equivalent to the forward lengthening of the delta of the lower alluvial 
plain. These flat alluvial patches may be seen even in torrents, sometimes 
reaching from one cascade to the other..... It is easy to perceive that 
these patches must be liable to constant change. They must be perpetually 
shortened by the recession of the lower barrier, and lengthened by the reces- 
sion of the upper ones. 7. These principles are eternally at work on all 
valleys, from the smallest to the largest” (174-176). 
The use of “horizontal” in describing the lower parts of 
valleys is curiously inexact in contrast to the keen recognition 
of the difference between what we should now call local and 
general baselevels, and of the aggradation of a flood-plain on 
account of the ‘“‘forward lengthening of the delta.” 
The balanced condition of rivers—Turning now more par- 
ticularly to the problem of river action, we find that the balance 
between erosion and deposition, attained by mature rivers, 
introduces one of the most important problems that is encoun- 
tered in the discussion of the geographical cycle. The develop- 
ment of this balanced condition is brought about by changes in 
the capacity of a river to do work, and in the quantity of work 
Here is a characteristic illustration of Greenwood’s mixture of sense and non- 
sense: “The very soil on which we tread .... may be said to be on its road 
from! the @hilltothessea-warmss No drop of rain x#zs an inch on the surface of 
the earth without, as far as it goes, setting some soil forward on its road to the sea, 
and it won’t run back again. No return tickets are given. It will wait there, and go 
on by the nex-trazz ” (105). 
