498 DISCUSSION : FORESTS, RESERVOIRS, AND STREAM FLOW 
Mr. Chitten- necessary as an adjunct to reservoir construction. Secretary Wil- 
den, 
son’s report, already quoted, says: “No matter what its purpose or de- 
sign, any reservoir system developed in the Southern Appalachians 
is foredoomed to failure unless. the watersheds that feed it are kept 
under forest;” and Mr. Leighton—‘the reservoirs will not be worth 
a minute’s time nor a cent of money unless the forests are retained.” 
Yet it seems that on the Cumberland and Tennessee, with deforestation 
already far advanced, it will take about 700-years to fill the reser- 
voirs 10%, and of course only a small portion of this can be traced 
to deforestation. 
The silt measurements of these streams also confirm, though from 
another point. of view, the writer’s conclusions, from observation and 
study of the rivers themselves, that our navigable streams are not 
shoaling appreciably more than formerly. 
At this point reference may properly be made to an argument 
advanced by two or three parties to this discussion, that soil cover 
is necessary over rocks because of its aid in disintegrating them, and 
also that trees are important in such places for the same reason and 
for the added reason that, by splitting up the rocks, they facilitate 
the ingress of water and its storage in the ground. In arguments of 
this kind one clearly traces the mental habit of the geologist whose 
very calling directs his study to the rocks of the earth and leads him 
to magnify both the extent and importance of those localities where 
rock is near the surface. Whatever force there may be in the argu- 
ment itself is neutralized by its very limited application. Forest roots 
do not penetrate to the underlying rock, except to a very small ex- 
tent, even in mountainous countries. In clearing the routes for at 
least a hundred miles of road in dense forest in the heart of the 
Rocky Mountains the writer does not believe that 5% of the trees re- 
moved penetrated to rock. Taking the whole country over, it cannot 
be that even one-tenth of 1% of the trees have any influence on the un- 
derlying rock. And so it is of soil covering; the areas where rock 
in situ lies within reach of the plow, or even within 2 ft. of the sur- 
face are very limited, and play an insignificant part in the general 
economy of the soil. 
Proposition 6. 
“As a general proposition, climate, and particularly precipitation, 
have not been appreciably modified by the progress of settlement and 
the consequent clearing of land, and there is no sufficient reason, 
theoretically, why such a result should ensue.” 
The correctness of this proposition seems to be generally conceded 
by those who have carefully studied the question. For every rain- 
fall record that forms an apparent exception, one can be found to off- 
set it. Both in this country and in Europe long-time records of pre- 
cipitation show little change, and certainly none in the direction of 
