?
xvi
10. Geology. Nature of underlying rock.
The rocks are all metamorphic, chiefly hornblendic gneiss. There are evidences of volcanic action close by the town, where trap has been injected into the decomposing gniess, thereby converting the mag-nesian base into a white mineral (magnesite). The gneiss in some instances has an appearance of stratification, and the beds are apparently displaced, tilted to an incline of 75°. In the neighbouring low range of hills magnetic oxide of iron is found in large quantity, and the Salem steel made from the local ores is of high repute. A conical hill near the Railway Station is made up almost entirely of veins of iron ore. Gneiss rock is exposed a good deal in the river bed, and generally is not far from the surface, in the area occupied by the town.
The soil on the uplands is rather thin and consists of a ferruginous loam, but in the valley near the river it is darker in colour and more clayey in texture. The soil of the town is somewhat calcareous, and has the property of nitrifying organic matter.
Earthquakes are not uncommon in the Salem and Shervaroy Hill districts.
11. Nature of soil and sub-soil and depth.
(a ) Temperature.
Not yet determined.
(b ) Porosity   ...
Do.
(c.)     Absorptive properties.
Do.
(d ) Chemical constituents.
Do.
(e.) Air in subsoil.
Do.
12. Malarial diseases when prevalent ?
Intermittent fever is endemic in the valley, and mountain slopes. It prevails mostly in the first quarter of the year, when easterly winds and great diurnal changes of temperature prevail. New-comers to the station are said to be particularly liable to it. The mountainous parts of the district are thought to be specially malarious just before the south-west monsoon has set in.
Connexion of Malaria with Cholera ?
There is some coincidence in the seasons of cholera and fever, as both appear most frequently in the cold weather months. Salem does not usually suffer in the first year of a cholera invasion. As it is one of the last districts to be attacked, it reproduces cholera for a longer time than most other places.
13.  Condition of Agriculture.
Very satisfactory.    The farming of the Salem valley is the best I have seen in India, so far as dry cereals, cotton, &c., are concerned.
(a.) Nature     of produce.
Cereal grains, oil seeds, cotton, tobacco, &c.
(b.)  Drainage...
From the tilted condition of the strata of rocks it is difficult to keep water in reservoirs in the valley. The tanks are dry early in the year, and fill again with the south-west monsoon. The general drainage of the valley is good.
(c.) Irrigation...
Practised wherever water is obtainable.
14. River banks.
The ordinary level of water in the  river is considerably below the bank levels.