257 
Part 4 .] Center: Note on Meh or Alkali Soils and Saline Well waters. 
8. The circulation of the sulphur that occurs in the earth is very interesting. 
That which forms the sulphates in the earth-water ap- 
Origin of sulphates. pears to he derived from the sulphurets, especially of 
iron, which are so universally diffused in rocks, and from the gypsum rocks, 
which, however, form an insignificant portion of the strata. The sulphate of 
lime heing moderately soluble may ho readily taken tip hy water. The sul¬ 
phurets become oxidised hy the oxygen in air or water, leaving red iron oxide, 
which gives the yellow or red colour to soils and clays; while the sulphuric acid 
attacks the silicates and unites with soda or lime. In the strata of the earth are 
found deposits of sulphates of lime, hut these appear to have been deposited from 
solution hy infiltration, or hy evaporation, as in the Salt Range. Their ultimate 
origin is probably the same as that just indicated. The presence of sulphate 
of lime in soils leads to the production of sulphate of soda. The former salt is 
slightly soluble, and as the earth-water contains alkaline cai’honatc, mutual 
decomposition leads to the formation of carbonate of lime and sulphate of soda. 
This partly accounts for the excessive proportions of sulphate of soda often 
found in I’eh. The sulphates may be again reduced to sulphides by organic 
matter from the vegetable mould or other sources, which accounts for the presence 
of sulphuretted hydrogen in dirty well waters rich in sulphates. 
9. As regards the chlorine of the alkaline chlorides, there is more difiiculty. 
Chlorine is not an important chemical constituent of any 
Origin of clilondes. common minerals forming rocks, but there is no rock 
that on being powdered and washed with distilled water does not show its pre¬ 
sence. The only explanation known of its appearance lies in the fact that, 
though generally in minute quantities, it is the most universally diffused sub¬ 
stance we know. Even in air a chemically clean platinum wii’e cannot bo 
exposed for some time without showing the sodium line in the spectroscope duo 
to sodium chloride which can be extracted from the air dust. 
10. There is next to be considered the chemistry going on in the decomposi- 
Forination of Balts in tion of the debris of the rocks forming the plain. It is 
tlio plains. in a more finely-divided state, and is therefore in a con¬ 
dition moi’o favourable for chemical action, and besides the constituents are in a 
further advanced state of decomposition than in the fresh rocks. The action 
that has been described is therefore intensified. It has been proved by experi¬ 
ment that it is from the most finely-divided clay (felspathio) particles of soils 
that most of the soluble substances can be extracted. These particles are so 
extremely fine that under the microscope they are seen only as minute dots. 
The other small particles which are of measurable dimensions are silicious, and 
yield to acids only a slight amount of soluble matter. 
11. There are three points to be considered,—the action that takes place on 
the surface, that which takes place in the strata permeated by the underground 
water, and also the relations between the two. 
12. On the surface undoubtedly the greatest amount of decomposition goes on 
Surface production of from the united action of air, moisture,, heat, and light. 
salts. This produces the perennial supply of soluble salt neces¬ 
sary for the growth of jdants, and in cultivation it is assisted by turning up and 
