Name of the Rock


Upper Miocene Pliocene

Dupi Tilla (2500 to 3000 feet)

Coarse Ferruginous soft sand tone with numerous layers of quartz and chert pebbles; clays sometimes sandy and mottled, occur at intervals. Pebbly sandstone conglomerate beds and fossil wood common.


Middle Miocene


Tipam (About 4000 feet)

Girujan Clay

Dark grey and bluish grey clay with mottling’s; lower part consists of ferruginous sandstones.

Tipam sandstone

Coarse and gritty ferruginous sandstone with interlayers of clays; sandstones are massive, cross bedded and yellowish brown colored; conglomerates in pockets; fossil wood and lignite (about 1600 feet thick in Sitapahar).


BokaBil (4000 - 6000 feet)

Upper unit

Bluish grey shales with conchoidal fracture lenses of hard calcareous shale.

Middle Unit

Alterations of 75 - 350 feet bands of massive and bedded sandstone and layers of shales and siltstones; lenticular and spheroidal concretions common at the top; fossiliferous conglomerates occasional.

Lower Unit

Thin bedded, bluish grey shales with intercalations of shaly siltstone.

Bhuban (7500 - 13,000 feet)

Upper unit

Bands of massive and sandstone with interlayers of siltstone at the top, laminated sandy shales interbedded with sandstone at the middle and alternation of sandstone and siltstone at the base.

Middle Unit

Predominantly a shaly and silty unit with numerous partings of arenaceous material; upper part sandy.

Lower Unit

Highly micaceous bedded to massive compact sandstones and fossil shales.