Mr. Smith. 
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362 DISCUSSION: FORESTS, RESERVOIRS, AND STREAM FLOW 
Geological Society of America to join the Members of the American 
Society of Civil Engineers in a discussion of the paper. 
While the author has everywhere exhibited the engineer’s desire 
to cover the ground thoroughly, his presentation of the subject omits 
any mention of important factors that lie beneath the surface, and 
the writer desires to call attention to certain of these well-known 
geologic conditions, although time has not permitted him to elucidate 
them with the thoroughness that characterizes the paper, and also to 
record a few observations made in the course of his geologic field 
work in the West, which apparently run counter to those cited by the 
author. 
In the discussion of the effect of forests on rainfall, the illustration 
used at the very beginning of the paper impresses the geologist as 
defective, and does not seem to “apply perfectly” in assuming a 
“practically impervious” subsoil or rock floor. Every geologist who has 
investigated underground waters would pronounce such an assumption 
as quite contrary to the facts and, indeed, did the assumed conditions 
actually exist, large areas of the United States would be without 
potable water. Throughout the paper the author’s failure to see any 
disposition for precipitation other than by immediate run-off and 
evaporation apparently leads him into a fundamental error that vitiates 
all his conclusions as to the effect of forests. In many parts of the 
country the underground supply—the water that saturates the soils 
and rocks—not only surpasses the surface flow in quality, but also 
exceeds it in quantity. The underground circulation of water is, there- 
fore, not a negligible but a most important factor. This is indeed the 
important factor in maintaining stream flow during dry periods, and 
the beneficial effects that geologists generally believe forests to exert 
are exerted through their influence upon sub-surface storage and 
circulation. 
In his casual mention of springs, Colonel Chittenden apparently 
regards these as of superficial and local origin rather than as marking 
the points of issue of water which may have traveled slowly for long 
distances and possibly at considerable depths. Again, many who have 
shared with the author the advantage of studying rivers at their sources 
will not agree with him that springs and small streams exercise but 
little regulative effect, on large rivers. On the contrary, in the case 
of streams without lakes or artificial reservoirs along their courses, 
all the dry-season flow may be regarded as being maintained by the 
slow escape into the.stream channels, by seepage or more definite 
springs, of water stored in the underground reservoirs earlier in the 
year, when rain was falling or snow melting. 
Keeping in mind the existence of underground water, it is at least 
interesting to review the forest argument. The forest mulch not only 
acts as a temporary: reservoir of limited capacity, but it contributes its 
