EECESSION OP CLIFFS. 
63 
a leaf. Every canon wall, throughout its trunk, branches, and twigs, and 
every alcove and niche, becomes a dissolving face. Thus the lines and area 
of attack are enormously multiplied. The front wall of the terrace is cut 
into promontories and bays. The interlacing of branch canons back of the 
wall cuts off the promontories into detached buttes, and the buttes, attacked 
on all sides, molder away. The rate of recession, therefore, is coiTespond- 
ingly accelerated in its total effect. 
The largeness of the area presents really no difficulty. The forces 
which break up the rocks are of meteoric origin. The agency which car- 
ries off the ddbris is the water running in the drainage channels. Surely 
the meteoric forces which ravage the rocks of a township may ravage 
equally the rocks of the county or state, provided only the conditions are 
uniform over the larger and smaller areas. And what is the limit to the 
length of a stream, the number of its branches and rills, and to the quantity 
of water it may carry ? It is not the area, then, which oppresses us by its 
magnitude, but the vertical factor — the thickness of the mass removed. 
But upon closer inspection the aspect of this factor also will cease to be for- 
bidding. 
F or if the rate of recession of a wall fifty feet high is one foot in a given 
number of years, what will be (ceteris paribus) the rate of recession in a 
wall a thousand feet high? Very plainly the rate will be the same.* If 
we suppose two walls of equal length, composed of the same kind of rocks, 
and situated under the same climate, but one of them twice as high as the 
other, it is obvious that the areas of wall-face will be proportional to their 
altitudes. In order that the rates of recession may be equal, the amount of 
material removed from the higher one must be double that removed from 
the other, and since the forces operating on the higher one have twice the 
area of attack, they ought to remove from it a double quantity, thus making 
the rates of recession equal. In the same way it may be shown that the 
* The geologist will no doubt recognize that this is a simple and unqualified statement of a result 
which is in reality very complex, and sometimes requiring qualification. But a candid review of it in 
the light of established laws governing erosion will, I am confident, justify it for all purposes here con- 
templated. Though some qualifying conditions will appear when the subject is analyzed thoroughly, 
they are of no application to this particular stage of the argument. The statement is amply true for 
the proposition in hand, and it wonld be hardly practicable, and certainly very prolix, to give here the 
full analysis of it. 
