BPSC 69th CCE Prelims General Studies · Question 92 of 144

Correct — A, a b c d 3 4 1 2, that is Dharwar–3, Vindhyan–4, Quaternary–1, Tertiary–2. Each pairing is fixed by the definition of the system itself, and three of the four need no Bihar knowledge at all. Dharwar takes 3. The Dharwar is India's classic Precambrian schist-and-greenstone succession, named from the country around Dharwad in Karnataka and carried on the Dharwar Craton — an Archaean continental block formed between about 3.6 and 2.5 billion years ago and reckoned the oldest part of the Indian peninsula, built of tonalite-trondhjemite-granodiorite gneisses, greenstone sequences and calc-alkaline granitoids. In the four-fold scheme Indian geography texts use — Archaean, Purana, Dravidian, Aryan — the Dharwars are the oldest metamorphosed sediments and are grouped with the Archaean basement, which is word for word what description 3 says. Vindhyan takes 4. The Vindhyan is a thick, essentially unmetamorphosed sedimentary pile, 'one of the largest and thickest sedimentary successions in the world', and its standard lithology is exactly the list in description 4: sandstone, limestone, dolomite, quartzite and shale. It is worth noticing that 4 is the only description that names constituents rather than an age or a place, and a list of sedimentary constituents can belong to a sedimentary cover and to nothing else on the card. In Bihar the Vindhyan is the south-western hill country — the Kaimur Range, the eastern arm of the Vindhyas, running about 483 km from around Katangi in Jabalpur district of Madhya Pradesh east to around Sasaram in Rohtas district of Bihar, north of the Son. Quaternary takes 1. The Quaternary is the most recent period of geological time, and in Bihar it is not rock in the ordinary sense at all but the deep alluvium of the Gangetic plain, laid down by rivers coming off the Himalaya in the north and off the peninsular plateau in the south. Description 1 describes a process of deposition rather than a composition, which is the giveaway. Tertiary takes 2, and the location is officially recorded: the Ministry of Mines told the Lok Sabha on 1 December 2021 that GSI had run a G4 reconnaissance survey for placer gold 'in parts of West Champaran district … in foothills of Siwalik Himalayas'. The Siwaliks are the youngest, outermost Tertiary belt of the Himalaya, made of sandstone and conglomerate that is the solidified detritus of the mountains to their north, with the rock generally dated between about 16 and 5 million years old — and West Champaran is the only district of Bihar that reaches them. One structural mercy is worth noticing: every one of those four pairs occurs in option (a) and in no other option, so a candidate certain of any single pair already holds the whole answer.

• (b)a b c d 1 3 2 4 — This code reads Dharwar–1, Vindhyan–3, Quaternary–2, Tertiary–4, and it inverts the geological column almost completely. It makes the Dharwar the depositor of alluvium, when the Dharwar Craton is Archaean basement between about 3.6 and 2.5 billion years old and the alluvium under north Bihar is younger than two million years — a gap of three orders of magnitude. It then calls the Vindhyan Archaean, conflating a sedimentary cover with the crystalline floor it was laid on, and puts the Quaternary in West Champaran, which is true of the Terai plain in a trivial sense but is not what makes West Champaran geologically distinctive. Finally it hands the sandstone-limestone-dolomite-quartzite-shale list to the Tertiary, when that list is the textbook signature of the Vindhyan; the Siwalik Tertiary is sandstone and conglomerate, poorly consolidated, with no dolomite or quartzite in the definition.
• (c)a b c d 2 3 4 1 — This code reads Dharwar–2, Vindhyan–3, Quaternary–4, Tertiary–1, and its central error is placing the Dharwar in West Champaran, at the far north-western tip of Bihar. West Champaran lies against the Himalayan foothills where the youngest rocks in the state are exposed and where the Main Frontal Thrust separates the Siwaliks from the Bhabar and the Terai; Dharwar-type basement in Bihar belongs to the opposite corner, the Chotanagpur fringe running south-east through districts such as Jamui, where the plateau's Precambrian rocks push north across the Jharkhand border. It repeats option (b)'s error of calling the Vindhyan Archaean, and then gives the Quaternary a hard-rock lithology of sandstone, limestone, dolomite, quartzite and shale, which is exactly what unconsolidated river alluvium is not.
• (d)a b c d 4 2 3 1 — This code reads Dharwar–4, Vindhyan–2, Quaternary–3, Tertiary–1, and like the other two wrong codes it gets no pair right at all — none of (b), (c) or (d) scores a single correct pairing, which is itself the tell — a useful thing to notice, because on a four-item match list an option with zero correct pairs is usually built by rotating the whole key, and spotting one certain pair eliminates it instantly. It gives the Vindhyan's lithology to the Dharwar, which would mean the oldest metamorphosed rocks in India were undisturbed sandstone and shale; it puts the Vindhyan in West Champaran, three hundred kilometres from the Kaimur where Bihar's Vindhyan actually surfaces; it calls the Quaternary 'part of the oldest Archaean rock system', pairing the two extremes of the geological column; and it makes the Tertiary the depositor of the Gangetic alluvium, when the Tertiary Siwaliks are the source material the rivers cut into, not the deposit they built.

Indian geography teaches the country's rocks as four broad systems arranged by age, and this question is a straight test of that scheme. The Archaean or Precambrian basement, with the Dharwar succession sitting on and within it, is the oldest — the Dharwar Craton dates from about 3.6 to 2.5 billion years ago — and it forms the foundation of the peninsular shield and hosts most of India's metallic minerals. The Vindhyan is a vast, largely undisturbed sedimentary cover laid over that basement, mainly sandstone, limestone, dolomite, quartzite and shale; it supplies building stone and cement-grade limestone rather than metals, and its basin has yielded what may be the earliest known multicellular eukaryote fossils, possibly 1.6 to 1.7 billion years old. The Tertiary is the era in which the Himalaya rose, and its youngest, outermost belt, the Siwaliks, is a pile of sandstone and conglomerate shed from the rising mountains onto their own foreland — a range some 2,400 km long from the Indus to near the Brahmaputra and 10 to 50 km wide, bounded on the south by the Main Frontal Thrust with the Bhabar and the Terai below it. The Quaternary is the last two million years or so, represented across northern India by the alluvium of the Indo-Gangetic plain. Bihar is one of the few states in which all four are present within one boundary.

Do not try to hold four independent pairings in your head; find one you are certain of and check which option contains it, because on this item every pairing is unique to a single option. The safest anchor is the Quaternary: in Indian physical geography 'Quaternary' and 'alluvium deposited by rivers' are close to synonyms, and only option (a) makes that pair. A second, equally safe anchor is Dharwar with the oldest Archaean rocks; again only option (a) has it. If you know the Vindhyan lithology list, that is a third independent route to the same option. The one description that needs Bihar knowledge rather than general geology is 'Can be found in the West Champaran district', and the reasoning there is directional rather than factual: West Champaran is the north-western corner of Bihar, pressed against Nepal at the foot of the Himalaya, so whatever surfaces there must be young Himalayan material — Tertiary Siwaliks — and cannot be ancient peninsular basement. That single directional insight also disposes of option (c), which would put Dharwar rocks in West Champaran. Underneath the whole question is Bihar's basic structure. India-WRIS states it plainly: 'The river Ganga cuts the state into two unequal halves, flowing from west to east. Physiographically, north Bihar is almost entirely a level tract while south Bihar is hilly and undulating.' The state's 94,163 sq km divide into three physiographic parts — the Shivalik tract in the north-west, the Gangetic plain across the middle, and the southern plateau fringe — and those three map almost exactly onto the Tertiary, the Quaternary and the older systems. One honest note on the vocabulary. In strict stratigraphy the Dharwar Supergroup is a Karnataka succession, and Bihar's Archaean basement is more properly the Chotanagpur gneissic country; 'Dharwar rock system' here is being used in the generic textbook sense of the oldest metamorphosed rocks associated with the Archaean, which is how state geography syllabi and this paper use it. Answer in the vocabulary the question is written in.

• The correct matching is Dharwar–3, Vindhyan–4, Quaternary–1, Tertiary–2, i.e. code 3 4 1 2 — and each of those four pairs occurs in option (a) alone, so any single certain pair settles the item
• The Dharwar Craton is Archaean, formed between about 3.6 and 2.5 billion years ago, and is reckoned the oldest part of the Indian peninsula — tonalite-trondhjemite-granodiorite gneisses, greenstone sequences and calc-alkaline granitoids; the western block carries greenstone sequences 3.0 to 3.4 billion years old
• The Vindhyan Supergroup is 'one of the largest and thickest sedimentary successions in the world'; the Vindhya basin has yielded what may be the earliest known multicellular eukaryote fossils, possibly 1.6 to 1.7 billion years old
• The Kaimur Range, Bihar's Vindhyan hill tract, is the eastern portion of the Vindhya Range: about 483 km long, up to 80 km wide, running from around Katangi in Jabalpur district, Madhya Pradesh, east to around Sasaram in Rohtas district, Bihar, north of the Son, with its escarpment forming the watershed between the Son to the south and the Tons to the north
• The Siwaliks, the Tertiary belt: about 2,400 km from the Indus eastwards to near the Brahmaputra, 10 to 50 km wide, sandstone and conglomerate that is the poorly consolidated detritus of the Himalaya, dated roughly 16 to 5 million years, bounded on the south by the Main Frontal Thrust with the coarse Bhabar zone and then the Terai springs below it
• Ministry of Mines, written reply in the Lok Sabha, 1 December 2021: GSI carried out G4 stage reconnaissance for placer gold 'in parts of West Champaran district … in foothills of Siwalik Himalayas', average concentration 0.0061 to 1.96 ppm, no resource estimated — the officially recorded presence of the Tertiary belt in that district
• The same reply places the whole of Bihar's primary gold-ore resource — 222.885 million tonnes of ore with 37.6 tonnes of contained metal — in the Sono area of Jamui district, in the old-rock country on the Chotanagpur fringe, which is the state's Archaean corner
• India-WRIS on Bihar's structure: 'The river Ganga cuts the state into two unequal halves, flowing from west to east. Physiographically, north Bihar is almost entirely a level tract while south Bihar is hilly and undulating'; the state covers 94,163 sq km with an average elevation of about 53 metres
• BPSC's own published remark on the 71st CCE recorded that 'River Karmanasa originates in Kaimur Hill' — the Kaimur upland being the surface expression of the Vindhyan in Bihar
• The Chota Nagpur Plateau, whose Precambrian rocks reach into south-eastern Bihar, covers about 65,000 sq km and is built of rocks older than about 540 million years

• Reading 'Quaternary rock system' as a hard rock — in Bihar it is unconsolidated alluvium, which is precisely why the matching description talks about deposition rather than composition
• Assuming West Champaran, being in Bihar, must expose old peninsular rocks — it is on the Himalayan margin, so what surfaces there is the youngest system in the state
• Treating Dharwar and Archaean as unrelated names, or reversing Dharwar and Vindhyan because both are associated with hills and minerals

BPSC likes this shape — a four-item match list in which three descriptions are pure general geology and exactly one is Bihar-specific, so the Bihar detail is what separates candidates while the rest is recoverable from a school textbook. The 69th also printed the two columns as separate blocks with the answer given as a bare code string, which is worth practising, because reading a code like '3 4 1 2' back onto a b c d under time pressure is its own small skill. Note as well that the Commission's descriptions mix categories deliberately: one is an age statement, one a lithology list, one a depositional process and one a district. UPSC never asks Bihar's rock systems, but it asks the identical geology in statement form — which system holds India's coal, whether the Dharwars yield petroleum, what the Gondwana beds contain — so the underlying preparation is shared and only the final localisation differs.

• practice — not a real PYQ

  The Siwalik or Tertiary rocks of Bihar are exposed mainly in which district?

  • (a)Rohtas
  • (b)West Champaran
  • (c)Jamui
  • (d)Munger

  Answer(b) West Champaran — the district sits at the foot of the Himalaya on the Nepal border, and the Ministry of Mines has recorded GSI reconnaissance for placer gold in the 'foothills of Siwalik Himalayas' in parts of West Champaran.

• practice — not a real PYQ

  Sandstone, limestone, dolomite, quartzite and shale are the principal constituents of which rock system?

  • (a)Dharwar
  • (b)Gondwana
  • (c)Vindhyan
  • (d)Siwalik

  Answer(c) Vindhyan — a thick, largely unmetamorphosed sedimentary succession; in Bihar it forms the Kaimur Range and the south-western hill country towards Rohtas.