COLORADO IRRIGATION WATERS AND THEIR CHANGES. 7 
ed in the content and composition of its mineral constituents while 
it is still within its mountain area and before it debouches from its 
canyon into the plains. As snow we may consider it free from any 
mineral content, and as river water it is very pure, but not free 
from mineral matter. It has already been at work upon the rocks. 
It has taken from the air some carbon dioxid and gotten a little 
more from the decaying organic matter with which it has come in 
contact, and with this to aid it, it has taken up from 2.5 to four or 
five grains of mineral matter to each imperial gallon that flows 
through its canyon. Even its flood waters find time enough to dis¬ 
solve out of the rock the smaller quantity, i. e., 2.5 grains per im¬ 
perial gallon. It may seem to some an incredible thing that this 
should be so, but we can imitate it, and show that in a compara¬ 
tively short time pure water in the presence of carbon dioxid can 
take up upwards of 4.5 grains of mineral matter per gallon from 
these very rocks, or rather from some of their constituents. There is 
no doubt about either the fact or the source from which the mineral 
content of the water is derived. The amount dissolved may sur¬ 
prise us, and we may wonder why the rocks have lasted so long, 
but we all know that the surface of the rocks is worn and that 
many of them are rotten for many feet below the surface, even 
crumbled so that they can be moved with pick and shovel. Some 
of the streets of the city of Denver are covered with such material 
as are our walks and drives. Those of us who have traveled on al¬ 
most any of our mountain railroads have seen cuts of five, ten or 
more feet in depth made through such material, aggregating many 
miles. The geologist finds everywhere the products left by the 
water; sometimes they are thick beds of clay, at others simply rock 
debris. He sees in the soil a testimony of its persistent action whereby 
it has loosened the bonds which bound the little grains now constitu¬ 
ting the particles of soil to their fellows, dissolving some, changing 
others, and carrying still others away. Each step that he describes* 
is susceptible of observation or direct proof, however slowly they 
may seem to proceed or however great their aggregate results. 
§ 15. The water of the Poudre, as already stated, is derived 
from the melting snows of the Laramie and Medicine Bow ranges,, 
but by the time it has reached its canyon it has taken up a con¬ 
siderable amount of matter from the rocks. If we assume the flow 
to be 300 second-feet and the dissolved matter to be 2.25 grains per 
imperial gallon, the amount of mineral matter removed from its 
drainage area per day would be close to twenty-six tons, or taking 
the specific gravity at 2.6, almost 320 cubic feet of solid rock ma¬ 
terial every twenty-four hours. Even these figures represent only 
the amount carried at this point in the course of the stream, and 
not the total chemical work done by\he water, for it is very prob¬ 
able that a series of changes have taken place, beginning with the 
