भूगर्भीय संरचना

A general scheme of the geology of India is given in the Imperial Gazetteer of India. It divided the rocks of the Peninsula into three great groups, called respectively the Archaean, the Purana and the Aryan, according to the period of their formation.

The Archaean Group is the oldest. It occupies more than half of the Peninsula. It consists of crystalline rocks of various kinds. The reason why they are grouped together is that they all appear older than any other rocks, but among themselves no one kind can with any confidence be said to be older than another. The most prominent of these rocks are gneisses and schists and the rocks of the Dharwarian system. Valuable minerals are found in the last named.

The Purana Group is next in point of antiquity. It consists of sediments, but as no marine fossils have been found in Peninsular India (except in strips along the coast) it is argued that these sediments were not left by the sea. In parts, as in the Cuddapah system, the thickness of this group is as much as 20,000 feet. It can be divided into lower and higher beds. The lower beds consist chiefly of ferruginous jaspers and procellanites, the higher of shales, limestones, and sandstones.

The Aryan Group is the most recent. It includes two great subdivisions the Gondwana system and the Deccan Trap.

The Godwana System is formed of sub-aerial and freshwater deposits. It is preserved in patches all over India. It is divided into the Lower and Upper Gondwanas, and further distinctions are made in these. In the Lower Gondwanas there occurs the Damuda series, which contains the most valuable of the Indian coal seams and sometimes has a thickness of 10,000 feet. In the Upper Gondwanas, the Mahadeva series, which consists chiefly of sandstone, also attains (in the Satpura area) a thickness of 10,000 feet.

In Yavatmal District the Archaean rocks were entirely covered by Puranic rocks. These were covered in turn by the Gondwana system. Next Deccan trap was spread over all. Finally the action of the atmosphere removed the Decan trap in parts, exposing, Gondwana and Lameta beds. During the last stage also alluvial soil, the common black cotton soil, was spread over parts of the District.

No Archaean rock has been noticed in the District. Purana rock is found at various places in the south. It consists of Shales, Slates, Limestones, and Sandstones. The Berar Gazetteer of 1870, p.14 says that the shales are deep red. Fine grained, with a somewhat nodular structure, much jointed, but irregularly breaking up into small, minute, angular fragments. Thin beds of limestone occur in them. Capital section of these rocks are seen in the Penganga and its tributaries. The beds throughout are nearly horizontal. In places, ribboned jasper is interstratified Chhota Arli is in Kelapur taluka. At Yenuk, in the south of Wani taluka there is a hill formed of Purana sandstone. It contains several bands of comglomerate in which pebbles of hematite are found. Iron-ore used to be made from this hematite.

Rocks belonging to the Gondwana system are also found in Wani taluka. They occupy its south eastern half. Like the Purana rocks they are often shales, slates, limestone, and sandstones. Unlike them they often take the form of coal. There is a large coalfield in Wani taluka which extends under the Wardha to Warora in Chandrapur District and under the Penganga into the Nizams Dominions. The Gondwana limestone are described as a grey earthly amorphous limestone, containing chert, in places, not in very large masses. At Wanjra above five miles north of Wani town a small hill is composed of pinkish limestone of this bed. West of Wani the limestone continues varying in colour from buff to dark grey, and contains chert, passing into jasper in tolerably regular layers.

To the west and north of Kayar there is deep angle in the trap and beds which are possibly Lameta are exposed. Deccan trap is spread over the greater part of the District. In the southern half it forms irregular hills, and some of these in Pusad taluka are nearly 2000 feet high. Alluvial soil pleiocene and Recent covers the trap along the north of the District below the ghats and in the larger valleys elsewhere.