BULLETIN 82. 
8 
first action of the pure water upon the rock particles whereby a 
part of the substances originally dissolved has been removed, and it 
is only that portion which has escaped removal from solution that 
we find in the water in the lower mountain section of the stream. 
In addition to this the remaining rock has also been altered, and 
its new condition represents a further fraction of the work accom¬ 
plished by the water. 
§ 16. This is, in general terms, a statement of the process by 
which our waters obtain their burden, be it great or small, of min¬ 
eral matter in these mountainous sections where the principal or 
only source from which they obtain it is the constituent min¬ 
erals of the rock by direct attack upon them; and the products so 
formed are not modified, except by the agencies universally present, 
as for instance, the air or the interaction of solutions, differing only 
slightly from one another. This is wholly changed, as we shall 
see, when we come to such conditions as prevail in the soils. A 
fuller consideration of the changes which we are able to trace will 
I think help us materially, both in answering the questions arising 
relative to the points of attack, the course of the changes taking 
place in the minerals, and prepare the way for a better understand¬ 
ing of the manner of formation and properties of the soil. The ob¬ 
ject of this bulletin, however, is to take up the study of the river 
water and the changes it suffers when used for irrigation, in so far 
as we may be able to unravel them; and if we do not succeed in a 
satisfactory measure we still hope that the data accumulated may 
be interpreted by others to the furtherance of the object here at¬ 
tempted. 
§ 17. I11 Bulletin No. 65, entitled “A Soil Study, Part III., 
The Soil,” I stated that, in my own view, the study reduced itself 
to an investigation of the various decomposition products of felspar; 
mot that other minerals might not be participants in these changes, 
but simply as a fact in this case, that we had an orthoclase felspar 
to deal with together with the products of its alteration. What 
these products are will undoubtedly vary under different conditions. 
Two conditions, however, obtain everywhere; the presence of water 
and of carbonic acid, and to these we appeal as the chief agents in the 
changes whereby, among others, the food elements contained in the 
rock particles of the soil are made available. It has been custom¬ 
ary to consider certain mineral combinations which were supposed 
to be formed by the action of various agents upon the rock particle^ 
within the soil as intermediate agents, serving the purpose of re¬ 
taining and conveniently giving up certain elements of plant food. 
This function has been attributed to a group of minerals called 
zeolites, and to express this property of the soil we find the expres¬ 
sion zeolitic constituents. So far as the study of the action of 
water on felspar goes, it throws no light upon this view, and we de- 
