46 
Colorado Experiment Station 
place that which evaporates annually from the land surface, if it be 
kept ordinarily moist. Under these conditions the silicic acid, calcic 
and magnesic salts pass out of solution, leaving the sodic salts. Any 
calcic sulfate that may be formed, together with the sodic sulfate, will 
be retained near the surface and will be brought up and deposited as 
efflorescences or disappear into the soil again, according to the supp y 
of surface-water or the weather, while the sodic carbonate in excess of 
what may be necessary to form calcic and magnesic carbonates will re¬ 
main in solution and in effect be concentrated therein by each annual 
increment. This may seen! too simple an explanation of the condition 
which we find in this northern section but I believe that it is the cor¬ 
rect one. 
The ground- and drain-waters in this section are quite similar in 
character, both carrying very significant quantities of carbonates. The 
ground-waters within 4 feet of the surface may carry sulfates princi 
pally but at a depth of 15 or more feet these give place to sodic car¬ 
bonate, and at considerable depths, though the total amount of salts in 
solution may exceed 100 grains to the imperial gallon, there is so good 
as no sulfates, while the sodic carbonate amounts to 90 or even more 
grains to the gallon. 
The chief difficulty in this explanation lies in our ideas of ar¬ 
tesian waters, i.e., that they are waters confined between impervious 
strata so curved that they form a series of basins one inside of the 
other and that the water between a pair of these irpervious strata is 
under pressure enough to force the water above the surface in the case 
of a flowing well. The wells referred to in this bulletin are all flow¬ 
ing wells. The water that flows into the valley is all mountain wate 4 * 
and contains sodic carbonate especially in such quantities as we find 
in the deeper wells only after it has been changed quite radically. The 
only way that the sodic carbonate can accumulate in the lower strata 
of these waters is apparently by passing through the strata into the 
water from above. I have mentioned the fact that theie are in one 
locality small beds of sodic carbonate on the surface, but borings have 
failed to show other deposits of this salt. 
■ LACK of drainage causes excess of alkali 
The only difference between the two areas is that the one is fairly 
well drained while the other is not, owing to the form in which the 
strata of the valley were laid down while this whole area was occupied 
by a fresh-water lake across which the Rio Grande built a bar, or fan. 
The water supplied to the valley has always been the same, i.e., 
the waters of the streams coming down irom the surrounding moun¬ 
tains, some of which are never entirely free from snow, and yet the 
artesian waters from the two sections are wholly different. 
