J. D. Dana on Denudation in the Pacific. 57 
style as the Hanapepe Valley. In the distant view the vertical 
channels appear very narrow; but when closely examined they 
are found to be deep and often winding passages. The precipice 
faces to the windward, and is directly under the whole line of 
peaks in the mountain range, both of which facts account for an 
abundance of water. Going to the westward along the range, 
the precipice changes to a sloping declivity, and these passages 
become déeper and longer, and more winding, just in proportion 
to the increasing length of the slopes: moreover at the same 
time they decrease in number. Where there is no slope to .col- 
lect the waters, the rills act independently, and their furrowings 
like themselves are small, narrow, and numerous ; but as the decliv- 
ity becomes gradual, the rills flow on and collect into larger 
streams, and the firrowings become deeper and more distant. Over 
this region, no distinction can be drawu as regards origin between 
these flutings and the gorges: and in respect to features, only this 
difference appears, that the size of the excavations is less and the 
number greater, the steeper the declivity. Ifa fissure be appealed 
to as the commencement of the longer valleys, it should also be 
admitted for each of the flutings. But this idea is wholly inad- 
missible. 
A brief review of the action of flowing waters with reference 
~ “i different results described may place this subject in a clear 
ight. net 
a. Suppose a mountain, sloping around like one of the volcanic 
domes of the Pacific—The excavating power at work proceeds 
from the rains or condensed vapor, and depends upon the amount 
of water and rapidity of slope. 
_ 4. The transporting force of flowing water* increases as the 
sixth power of the velocity,—double the velocity giving sixty- 
four times the transporting power.—The eroding force will be 
c. Hence, if the slopes are steep, the water gathering into rills 
excavates so rapidly, that every growing streamlet ploughs out a 
gorge or furrow ; and consequently the number of separate gorges 
a ted large, and their sizes comparatively small, though of great 
epth, 
fifty-five tons; a current of twenty miles an hour would, according to the same law, 
move a block of three hundred and twenty tons: again, according to the same law, 
4 current of two miles an hour would move a pebble of similar form of only a few 
ces “in weight.”—On the Transport of Erratic Blocks, Trans, Camb. 
1844, viii, 291, 233. 
 Srconp Series, Vol. LX, No. 25,—Jan., -_ 8 
