TIeadden — SllieiG Acid in Mountain Streams. 169 



Aet. XYIII. — Significance of Silicic Acid in Waters of 

 Mountain Streams ; by W. P. Headden. 



While engaged in sonae work on the waters of the San 

 Luis Valley I was struck by the unusually high percentage of 

 silicic acid, from 25 to upwards of 40 per cent, in the residues 

 obtained on evaporation. I was, at the time, inclined to 

 attribute this to some accident, or perhaps error. The water 

 had been shipped in jugs, and this may have had some influ- 

 ence, but several conditions lead me to believe that this influence, 

 if any at all, was wholly negligible. The water was evapo- 

 rated as soon as possible after it was received at the laboratory, 

 so that the water was in these jags but a few days — from seven 

 to ten at the longest. The quality and character of the resi- 

 due did not support this view, and the action of the water on 

 the jugs may be left out of consideration. 



The waters to which reference is here made were of excel- 

 lent quality and were either artesian or spring waters, but I 

 also observed that the water of the Rio Grande del Korte, at 

 Del Norte, was richer in silicic acid than is usual for river 

 waters, and richer here than further down the stream. There 

 was nothing in the composition of the dissolved mineral matter 

 apparently worthy of special attention except it be the high 

 percentage of silicic acid, ^nd while this was common to sev- 

 eral waters from different sources, I did not feel that this 

 characteristic was sufliciently well established to entitle it to 

 acceptance. We gained but little that at the time would 

 bear any interpretation, beyond the fact that the spring and 

 artesian waters of this large basin are of exceptionally good 

 quality. This statement does not apply to a subordinate basin 

 in which the towns of Mosca and Garrison, formerly called 

 Hooper, are situated. The wells of this basin at a depth of 

 500 to 880 feet yield a brown water rich in alkalies, but rela- 

 tively and as a rule absolutely poorer in silicic acid than the 

 artesian waters. 



There are a number of springs along the eastern margin of 

 the valley and some larger ones in the southern part of it, the 

 waters of which are of good quality and carry from 5*3 grains 

 to 17'6 grains of mineral matter to the imperial gallon, of 

 which silicic acid constitutes as much as 30 per cent. 



This line of work was laid aside in order to take up others 

 which seemed more urgent and perhaps more important also, 

 but recently, while studying the changes suffered by river 

 waters used for the purposes of irrigation, my attention has 

 again been called to the presence of silicic acid as a character- 

 istic mineral constituent of the waters of mountain streams 



