IOWA ACADEMY OF SCIENCE 
125 
quately safeguarded by the adoption of methods which will be de- 
scribed in detail further on.” 
On the same point, Mr. Henry Alvord makes this statement : 
“The watershed of the Cedar River above the intake appears to 
be one of the most extensive areas of porous soil utilized for natural 
filtration of a public water supply which it has ever been my fortune 
to observe. The glacial drift of which it is composed consists of 
coarse and fine gravels intermingled to a depth of some hundreds of 
feet. We looked in vain for traces of clays or finer soils. The 
surface mould is thin for the most part, and the level of the soil 
water on the benches and plateaus back from the river is evidently 
at a great distance below the surface, as indicated by the location 
of springs and the depth of the eroded streams. There is little or 
no surface run-off of the rainfall. Numerous potholes exist, depres- 
sions without visible outlet, and there was scarcely observed a dry 
run of any kind, or rivulet, save those of running streams, few in 
number, which were marked upon our map. 
The unusual porosity of the soil may be best illustrated by the 
statement that in passing over the located line of the railway, 
eleven miles along Cedar River, no run or rivulet or surface indi- 
cation of any kind was observed leading into the stream which 
would indicate that the rainfall passed over the surface of the 
ground. We also observed that in passing over the Northern 
Pacific Railway, which crosses the watershed from north to south, 
no pains was taken by that company to ditch its tracks, to provide 
small culverts, or even, in the case of very considerable depressions, 
to arrange for the passage of water from one side of its embank- 
ment to the other. The soil, therefore, of this valley is a porous 
one, receiving the copious rainfall of this region and largely ab- 
sorbing it, and by slow percolation filtering it to an unusual degree, 
thus creating the clear streams and exceptionally pure water.” 
Prof. G. W. Bissell says: 
“The Cedar river watershed is formed in a vast deposit of glacial 
drift, from which the river and its tributaries have eroded channels 
in general to the solid rock. In the case of the Cedar river intake, 
there have been probably three different shore lines in the past, 
which have existed long enough to form benches, or steps, in the 
slopes of the river valley sides, this being especially noticeable in 
the vicinity of Barneston. Except where clearing for railroads, 
trails, logging purposes or by fire has been effected, the whole 
watershed is heavily timbered. Most of the surface of the water- 
shed is very sloping, and much of it is very steep ; the benches and 
