170 Headden — Silicic Acid in Mountain Streams. 



whose collecting grounds are granitic areas and whose courses 

 have not yet traversed a long enough reach of open country, or 

 the plains, to have received either water from collecting areas 

 of a different character or drain waters from lands adjacent to 

 their courses. 



I shall now set forth such facts as have fallen under my 

 observation which seem to me to amount to reasonable proof 

 that this high percentage of silicic acid, varying greatly within 

 the limits of 15 and 46 per cent, is, in the instances which 1 

 have studied, specifically due to the action of water and carbon 

 dioxid, and, perhaps, also of the acid products arising from the 

 decomposition of vegetable matter on the felspars of the gran- 

 ite of the region. The action of the organic matter on the 

 felspars is, in the first phase of their decomposition, at the very 

 utmost insignificant if not nil, such, at least, is the result 

 obtained by an experiment made to ascertain how great a part 

 is played l3y such agents. In passing I will mention, apropos 

 to the presence of organic matter, the fact, that on evaporating 

 a large quantity of water from our mountain streams, from the 

 Cache a la Poudre for instance, one obtains at last a solution 

 which is strongly colored by humus-like substances and pos- 

 sesses an extremely disagreeable odor. In the case of the 

 Cache a la Poudre water used there was no question of pollu- 

 tion by sewage, for in all the distance traversed by its waters 

 from their several sources to the point where the samj)le was 

 taken, a distance of about sixty miles, the total population does 

 not exceed 150 souls, and the number of cattle grazing in this 

 district is so small that the question of pollution arising from 

 either of these sources is absent, and would be even if the flow 

 of the river were very small, but this seldom falls as low as 

 200 second feet and is usually much greater — still this water, 

 when larger quantities of it are evaporated down, shows the 

 presence of a significant amount of organic matter which, 

 despite its odor suggestive of an animal origin, I feel justified 

 in assuming to come from decaying vegetable matter. I shall 

 subsequently set forth the facts on which I base the statement 

 that this organic matter plays no important role in determin- 

 ing the amount and character of the mineral matter dissolved 

 out of the rock and carried in solution in such river waters. 



The amount of silicic acid usually carried by river waters is 

 small, the maximum shown in the analyses of forty-five Euro- 

 pean river waters being 21 per cent of the total solids, the Phine 

 at Strassburg, which carried in the sample analyzed 16'1 grains 

 mineral njatter per gallon — but this sample seems to have been 

 an exception even for the Phine, for other samples of its water 

 show much smaller quantities of substances in solution and 

 materially lower percentages of silicic acid ; at Basle for instance, 



