[The section on Geology is contributed by the Director General, Geological Survey of India, Calcutta]

The Great Trap region of the Deccan covers the whole district. It is entirely of volcanic formation. The volcanic portion consists of compact, stratified basalts, and an earthy trap. The basalts are the most conspi­cuous geological feature. To the west they lie in flat-topped ranges, separated by valleys, trending from west to east. In some flows the- basalt is columnar and then it weathers into the fantastic shapes. The formation at the base of the traps is chiefly amygdaloidal, containing quartz in ­vertical veins, crystals and zeolitic minerals, especially apophyllite wea­thering into a grey soil.

The absence of laterite, which caps the summits of the hills to the south, is a curious feature in the geology of the area.

The basalt is either fine textured or it is coarse and nodular.

Soils : As regards the soil, the valleys are filled with disintegrated basalt of various shades from grey to black, washed down by rain. It is of argillaceous nature. This soil is not favourable to the growth of large trees but it is very fertile for cereals and pulses. The black soil contains high alumina and carbonates of calcium and magnesium with variable amounts of potash, low nitrogen and phosphorus. The red soil is less common and is suitable for cultivation under a heavy and consistent rainfall.

Economic Minerals : Lime nodules and Kankar are found practically all over the district. The lime nodules yield a very good lime, slightly hydraulic, but not sufficiently so to be used under water. Mixed with pounded bricks and sand it forms a fair mortar. The trap rock is very useful for building purposes.

Occurrence of iron ore is reported near Bhadra in the Surgana mahal. The deposits consist of magnetite and ilmenite sands occurring in sporadic patches, but it is not of any economic significance.