2G0 
Eecorils of the Geological Surrey of India. 
[yol. xui. 
the disfiosition of the strata. If, however, a canal were made on a natui’al line 
of drainage, as I have heard the Western Jumna Canal is, it might influence the 
adjoining ground in the Avay I have mentioned in the case of rivers, both as to 
the water-level and quality of percolating water. 
15. When rain water sinks into a soil containing soluble salts, it dissolves them 
Natui-o of roll and its find carries them down till it reaches an impermeable 
varieties. stratum. Medlicott has pointed out the action of the first 
rain drops in carrying efflorescent .salts down, so as to be in a great measure out 
of the reach of the surface scour of the succeeding rainfall. If the soil is porous, 
it may gravitate down to the water stratum, which then becomes a reservoir of 
the surface salts. If it is only slightly porous, as in alluvial soils containing 
much clay, the soakage is only superficial to one or more feet in depth, and gene¬ 
rally in such cases the surface soil is more or less porous from atmospheric 
exposure, and below it lies a more compact clay subsoil. As rain water contains 
free carbonic acid, it dissolves also carbonate of lime and magnesia if these bo 
present in the soil. When evaporation succeeds, it draws up the moisture in the 
more porous surface soil by capillary action. As the water and carbonic acid 
pass off, the solution becomes more concentrated and carbonate of lime is re- 
deposited. This last action takes place first, and as the concentrated solution is 
drawn up to the surface, it finally deposits its most soluble salts on drying as an 
efflorescence on the surface. An essential condition is the dryness of the climate. 
In more temperate, but dry regions, as in the Utah Basin and the elevated j)arks 
or plateaus of the rocky mountains, offlorescences ajjpoar as well as in the scorch- 
ino- plains of India. The action, however, is intensified by heat, which increases 
evapoi-ation. By similar capillary action the moisture will creep up the sides of 
objects lying on the ground, such as pieces of brick, and deposit a coiDious 
efflorescence. At first it appears in glittering crystals, but as the sodium sul¬ 
phate gradually loses its water of crystallization, it breaks irp into a copious white 
powder of anhydrous salt, and it is then tl at it is most apparent. The carbonate 
of soda behaves similarly, but the sodium chloride does not, having no water of 
crystallization. Nitrate of soda and lime deliquesce in damp air. During the 
hot months, the salts, if brought up by rain, melt in their water of crystallization. 
By the word efflorescence we do not mean here what is known as such in chemi- 
cal language, that is, the breaking rrp of a crystallized salt into a powder from 
loss of water of crystallization. What is meant is efflorescence in the physical 
sense or the ajapeai'ance on the surface of the ground of soluble salts brought up 
by capillary evaporation. It is true that sulphate and carbonate of soda effloresce 
in the chemical sense, but chlorides and nitrates do not. 
16. From what has been explained regarding the origin of the salts dissolved 
out of the earth, it can be understood how the solutions can naturally be divided 
into two groups, whether they be river and canal waters, or well waters, or solu¬ 
tions formed when rain water soaks a saline soil. There are first the neutral 
solutions from which carbonate of soda has almost or entirely disappeared, hav¬ 
ing been used up in decomposing any soluble lime or magnesian sulphate or 
chloride and precipitating their carbonates. To this belong the river and canal 
waters, the chief ingredient of which is carbonate of lime with less amounts of 
