232 
THE GEAED CABON DISTEIOT. 
“ WJiere a stream has all the load of a given degree of comminution 
which it is capable of carrying, the entire energy of the descending water 
and load is consumed in the translation of the water and load, and there is 
none applied to corrasion. If it has an excess of load its velocity is thereby 
diminished so as to lessen its competence, and a portion is dropped. If it 
has less than a full load, it is in condition to receive more, and it corrades 
its bottom. A fully loaded stream is on the verge between corrasion and 
deposition. * * * The work of transportation may thus monopolize a 
stream to the exclusion of corrasion, or the two works may be carried for- 
ward at the same time. 
“The rapidity of mechanical corrasion depends on the hardness, size, 
and number of the transient fragments, on the hardness of the rock-bed, 
and on the velocity of the stream. * * * The element of velocity is 
of double importance, since it determines not only the speed, but to a great 
extent the size of the pestles which grind the rocks. The coefficients upon 
which it in turn depends, namely, declivity and quantity of water, have the 
same importance in corrasion that they have in transportation. 
“ Let us suppose that a stream endowed with a constant volume of 
water is at some point continuously supplied with as great a load as it is 
capable of carrying. For so great a distance as its velocity remains the 
the same it will neither corrade nor deposit, but will leave the declivity of 
its bed unchanged. But if in its progress it reaches a place where a less 
declivity of bed gives a diminished velocity its capacity for transjDortation 
will become less than the load, and part of the load will be deposited; or 
if in its progress it reaches a place where a greater declivity of bed gives 
an increased velocity, the capacity for transportation will become greater 
than the load, and there will be corrasion of the bed. In this way a stream 
which has a supply of ddbris equal to its capacity tends to build up the 
gentler slopes of its bed and cut away the steeper. It tends to establish a 
single uniform grade. 
“ Let us now suppose that the stream, after having obliterated all the 
inequalities of the grade of its bed, loses nearly the whole of its load. Its 
velocity is at once accelerated, and vertical corrasion begins through its 
