I 
19 
The Waters oe the Rio Grande 
ANALYSES OF THE SOIL SAMPLES DRIED AT 100° C. 
Soil 7 inches Subsoil Sample 
deep 
10 inches 
Percent 
Percent 
Insoluble (sand) . 
. . 56.271 
51.285 
Soluble silicic acid. 
. . 17.531 
11.662 
Sulfuric acid . 
0.255 
0.128 
Phosphoric acid . 
0.651 
0.019 
Carbonic acid. 
3.956 
10.207 
Chlorin.'. . 
0.462 
0.184 
Calcic oxid . 
6.900 
14.318 
Magnesic oxid . 
1.618 
1.444 
Potassic oxid . 
1.047 
1.183 
Sodic oxid . 
1.464 
0.679 
Ferric oxid . 
4.420 
3.567 
Aluminic oxid . 
3.382 
2.868 
Manganic oxid . 
0.192 
0.161 
Ignition . 
1.867 
3.085 
Sum . 
Oxygen equivalent to 
. . 100.017 
100.790, 
chlorin . 
0.104 
0.042 
Total . 
. . 99.913 
100.748 
Total Nitrogen . 
0.071 
0!050 
These analyses show that the soda salts were very largely in the 
top 7 inches of soil and that the calcium carbonate probably was con¬ 
centrated below the surface soil which was, at this place, 7 inches 
deep. Our marls sometimes contain calcium as a silicate. This may, 
by giving rise to soluble double silicates, account for the hijgih silicic 
acid in some of the alkalis. 
The preceding samples of alkali were all taken in the latter part 
of the summer, mostly in the month of August. This is a season when 
the general prevalence of *alkali is not apparent as in mid or late 
spring, especially after light snows or rains. At this time we some¬ 
times find areas of several square miles in a body white with these 
alkalis. 
The following sample was taken on 8 May, 1916, in the same gen¬ 
eral section of country in which the preceding samples were taken. 
This land has never been cultivated, so I doubt whether it has ever 
been irrigated. The principal vegetation is chico and (greasewood 
(Sarcobatus and Bigelovia ). The surface of the ground at this time 
was perfectly white over an area of many, probably 15 or 20 square 
miles. 
