The Ground Water. 
33 
which it forms 27 per cent, of it. But, remembering that this sul¬ 
fate does not pass into the drain waters, while it usually exceeds 10 
per cent., often rises above 17 and sometimes reaches 23 per cent, of 
the salts in the ground water, it seems strange that the water- 
soluble portion of the soil should so frequently give good reason for 
supposing it to be absent. I do not know any facts nor have I seen 
any statement of established or probable changes which will account 
for these facts as observed. 
§ 93. The magnesic and sodic sulfates are both present in the 
ground water, or their ions are, and constitute the efflorescent salts 
passing out of solution at the surface of the soil, or where the surface 
of the solution comes in contact with the air. Evaporation is pro¬ 
ceeding at this surface and the capillary movement of the ground 
water is rapid and free, for when the condition of the soil is such 
that we can sufficiently impede the capillary rise of the water, we 
prevent the formation of such incrustations. The result may be 
roughly presented as the movement of a free solution through the 
interstices of particles which are themselves not free to move, but 
capable of being modified in regard to their composition either by 
exchange or by attracting to themselves and retaining other salts. 
These processes may be subject to the greatest variety of modifica¬ 
tions, so that they are not exclusive or constant, and seldom per¬ 
fected, but vary from point to point within the soil. 
§ 94. It has been, accepted for a long time that soils as a rule 
have a high power of retaining potassic salts and but a very feeble 
one of retaining soda salts. If this were wholly correct, we should 
expect to find the drain waters from such areas as the one forming 
the subject of this study loaded with soda salts, at least to the same 
extent, if not to a much greater one, than the ground waters. But 
we do not find this to be the case, and the conditions are such that 
it is not probable that the difference is due to the dilution of the 
drain waters from this area by water from other sources. 
§ 95. Under the subject of the total solids in the ground 
water, I stated the result of experiment to be an indication that 
they decreased with depth, that the first foot of water after entering 
tht water plane was richer in total solids than the second, and so 
on. At first I did not believe this. An instance in point was well 
D, which on September 20th showed the presence of 3.4071 parts 
total solids per thousand. A temporary well opened on this date 
40 feet south of well D, the surface contour and the character of the 
soil being the same but the sample of water being obtained at a 
greater depth, probably two feet deeper, showed only 2.18713 parts 
total solids per thousand. The residue from the water of well D 
showed the presence of 16.87 per cent, of sodic sulfate, while that 
from the newly opened one showed 14 per cent., a difference of 
