DISCUSSION: FORES''S, RESERVOIRS, AND STREAM FLOW 395 
forest control of run-off, viz.: “By storing the waters from rain and Mr. Leighton. 
melting snow in the bed of humus that develops under forest cover, 
preventing their rapid rush, * * * .” If this means strictly what 
it says, the author believes that the bed of humus is the agent of 
storage. The impression here conveyed is intensified by the practical 
illustration given under the caption “Effect of Forests Upon the Run- 
Off from Rainfall,” in which an inclined-plane surface is used, 
“practically impervious to water, with a layer of sand covering some 
small portion of it.” The author has forgotten the greatest reservoir, 
namely, the ground. When he assumes an inclined-plane surface, im- 
pervious to water, he denies the existence of ground storage. The 
speaker has never before heard the principle of forest cover so applied. 
The common understanding is that the forest mulch is not the storage 
agent in any except a merely nominal sense. Its whole function is 
to protect the ground, so that its surface will not become hard and 
impervious, and to conduct the water of precipitation into the inter- 
stices of the underlying soil. The effects of this fundamental miscon- 
ception are apparent in many parts of the paper, and, in fact, the 
whole argument relative to the inefficiency of forests in conserving 
water is based upon it. Were the author’s original conception correct, 
then indeed would his conclusions have a measure of justification, but 
not otherwise. 
Although Colonel Chittenden denies that there is a pervious soil 
under the forest, he readily grants that there is a marked retentive 
capacity in bare soil. The reader must infer, either that there is no 
soil under the forest, or that soil covered by forest must in some way 
remain impervious. The really fatal admission, however, is in the 
sentence: “In newly plowed ground it (the retentive capacity) is 
probably greater than in the forest.” There is a reason why newly 
plowed ground is, as the author implies, more retentive than un- 
plowed, bare soil. This reason is that the compacted surface crust 
has been broken, the underlying earth has been disturbed and loosened, 
and thereby made absorbent to the precipitated water that falls upon it. 
After the rains have descended, and the sun has shone on this plowed 
ground for a period, a compact surface is gradually formed. The 
result is that the water is less easily absorbed and the retentive 
capacity of that particular piece of ground constantly decreases, ag 
the date of plowing recedes. 
What now is the effect of the forest-mulch cover? It protects the 
ground from the direct pelting of the rain and the resulting process by 
which the earth’s crust becomes compact, and keeps it in a condition 
that is always equivalent to that of a newly plowed: field. No one 
who has ever scratched away the mulch cover in a forest can deny this. 
The earth below is always found in an open and porous condition. 
How, then, can the retentive capacity of a newly plowed field be 
