BULLETIN 82 . 
54 
examine what the results of the bigger practice, i. e.,the irrigation 
of the whole valley may show. 
§ 100. I have stated that seepage or return waters begin to 
enter the river almost immediately upon its leaving the mountains, 
and have cited the increase in the total solids in the river water 
between a point above the North Fork and the water works, in 
support of it. The amount of such water increases as we go down 
the river. 
§ 101. We can present the matter thus: The water of the 
Poudre is taken from the river, used for irrigation, and after a 
time returns. The return waters have passed through or flowed 
over the soil. The amount returning to the river as waste water, is 
so small that I would not take note of it, even if I had sufficient data 
to justify me in attempting to do so. But I have not such data. 
Much of the water appearing in the lower part of the river has 
doubtlessly been used several times, but I doubt whether its com¬ 
position is, on this account, any more or less indicative of the 
effects of the irrigation waters upon the soil, or of changes which 
take place within the soil, than water which has not been used re¬ 
peatedly. I am inclined to think that in such cases the composi¬ 
tion of the return waters is dependent almost wholly upon 
the character of the soil from which it last issued. This question 
is of great importance in interpreting the results of the analysis 
of return waters. The river bed may be bordered by a margin of 
low land, as it frequently is, the water draining from the higher 
land having to pass through this, either in small streams or by the 
slower method of percolation. In either event there is opportun¬ 
ity for a material modification of the composition of the water. 
Still, as has already been said, we have in the return waters the 
result of all the changes, and a measure of the effects produced by 
irrigating, not a field, but a whole section of country. Our meas¬ 
ure is essentially the drain water of all this larger section, and in 
this case drain water means water that has passed through, not run 
over, the soil as rain water or as waste water from ditches. 
§ 102. In order to save space and bring the analyses of return 
waters together, I will anticipate a little and introduce the analy¬ 
sis of the Platte river water below the mouth of the Poudre, it 
being return water, but I shall give those of the Poudre the first 
place, not only in order, but in importance. 
