DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 469 
in country towns of 10000 to 20 000 inhabitants, and are as completely mr. Chitten- 
excluded from absorptive activity as is the ground under a city nee 
pavement. 
On the whole, it may be considered entirely probable that, acre 
for acre of ground otherwise similarly conditioned, the cleared land, 
particularly if under cultivation, will hold and transmit to the ground 
below more water than will the average forest. What makes the run- 
off in the open country more rapid generally than in the forést is 
drainage (including in that term roads and their ditches, regular 
drainage trenches, tiling, furrows of cultivated fields, etc.), and the 
roofs and pavements of towns; and it is due to these features, mainly, 
that the writer’s first proposition has a limited application. Omit these 
features, and the reverse would more than likely be true. 
The criticism, by Messrs. Swain, Pinchot, and Leighton, of the 
writer’s “ideal illustration” in the beginning of the paper, because of 
his use of the words “practically impervious” is, to say the least, 
captious, and comes with particularly bad grace from Mr. Pinchot who 
himself has made public use of identically the same kind of illustra- 
tion. Surely his “photograph of a denuded hillside” from which water 
sprinkled thereon “disappeared instantly” was practically impervious. 
In fact, one can rarely make a model which will represent natural 
conditions accurately, and the best that can ordinarily be done is to 
take an ideal case, and then note its departure from such conditions. 
This is what the writer did. No sooner had he stated his illustration 
than he hastened to explain that it was “never fully exemplified in the 
cleared land and the forest; and that there was always an absorptive 
capacity in soil without any covering; but, that the principle of the 
illustration applied perfectly, viz., that there were times when the 
greater retentive capacity of the forest was so far exhausted that it 
was powerless to act further, and there were other times when it was 
great enough to absorb all the precipitation that came to it. 
The writer, however, might, with perfect correctness, stand upon 
the literal application of his illustration, if he chose to do so. He was 
illustrating the difference in absorptive or retentive capacity of the 
forest and the open country. It would have been entirely proper to 
have eliminated those features common to both, such as slope and 
the capacity of the subjacent soil to take up moisture from above, and 
thus consider the ground in both cases as impervious. It would simply 
have been subtracting the same quantity from both members of the 
equation, and would not have affected in the least the principle involved. 
Upon the-basis of this distorted construction of the writer’s words, 
extreme conclusions have been drawn. These are perhaps sufficiently 
indicated by Mr. Leighton’s statement that the writer “denies that 
there is a pervious soil under the forest”; and again that he “denies 
the existence of ground storage.” No word can be found in the entire 
