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Q1 (IAS/2026) Geography › Indian Physical Geography Official Key

Consider the following assertion:
In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa.
Which of the following is/are the basis of the above assertion?
1. The Nadi-Sukta of the Rigveda
2. The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
3. The presence of the same species of dolphins in both the Indus and the Ganga river systems
Select the answer using the code given below:

Result
Your answer: —  ·  Correct: D

Explanation

The assertion relates to the Indo-Brahm (or Shiwalik) River hypothesis proposed by geologists E.H. Pascoe and G.E. Pilgrim, which suggests that a mighty river once flowed longitudinally along the Himalayas during the Pleistocene epoch, connecting the present-day Indus and Ganga systems.

  • Statement 1 is incorrect: The Nadi-Sukta of the Rigveda describes the river systems as they existed during the Vedic period (Holocene epoch), not the Pleistocene epoch.
  • Statement 2 is incorrect: Robert Bruce Foote is renowned as the father of Indian prehistory for discovering Paleolithic tools (e.g., at Pallavaram). The geological explorations regarding the Indo-Brahm river and the shifting of the Sutlej/Yamuna were conducted by Pascoe and Pilgrim.
  • Statement 3 is correct: A major biological evidence supporting the past connection between the Indus and Ganga river systems is the presence of the South Asian river dolphin (Platanista gangetica) in both basins. Since these dolphins are strictly freshwater species and cannot survive in the sea, their distribution indicates that the Indus and Ganga systems were once interconnected.

Thus, only statement 3 provides a valid basis for the assertion.

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Consider the following assertion: In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamu…
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Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 7.5/10 · 2.5/10
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This is a high-quality, multi-disciplinary question that merges Physical Geography (Pleistocene river shifts), Ancient History (Vedic texts), and Environment (biogeography of dolphins). It tests whether you can connect the 'Indo-Brahma River' geological theory with its actual scientific and historical proofs.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Historical and geological evidence for the Yamuna flowing into the Indus or the Sutlej flowing into the Yamuna during the Pleistocene period.
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > Evolution of the Himalayan Rivers > p. 7
Presence: 5/5
“These developments brought a reversal in the direction of flow in the middle section of the severed stream, i.e., the Ganga of today, resulting in its taking a southerly course and eventually annexing the Yamuna and its tributaries. Earlier, the Yamuna had a south-westerly course and was a tributary of the Indus. This entire event was completed by the late Pleistocene period leading to the evolution of the present drainage systems of northern India. Pascoe's and Pilgrim's concepts about the origin of the Himalayan drainage systems have been criticised on the following grounds: • (i) It is not necessary to postulate a stream of the size of Shiwalik River flowing all along the longitudinal extent of the Himalayas to explain the occurrence of the Shiwalik alluvial deposits and the boulder beds.”
Why this source?
  • Explicitly states that the Yamuna previously followed a south-westerly course and served as a tributary of the Indus.
  • Confirms that the reversal of flow and the annexation of the Yamuna by the Ganga system was completed by the late Pleistocene period.
  • Attributes the evolution of the present northern Indian drainage system to these specific Pleistocene developments.
INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.) > Chapter 3: Drainage System > EVOLUTION OF THE HIMALAYAN DRAINAGE > p. 20
Presence: 4/5
“It is opined that in due course of time Indo– Brahma river was dismembered into three main drainage systems: (i) the Indus and its five tributaries in the western part; (ii) the Ganga and its Himalayan tributaries in the central part; and (iii) the stretch of the Brahmaputra in Assam and its Himalayan tributaries in the eastern part. The dismemberment was probably due to the Pleistocene upheaval in the western Himalayas, including the uplift of the Potwar Plateau (Delhi Ridge), which acted as the water divide between the Indus and Ganga drainage systems. Likewise, the downthrusting of the Malda gap area between the Rajmahal hills and the Meghalaya plateau during the mid-pleistocene period, diverted the Ganga and the Brahmaputra systems to flow towards the Bay of Bengal.”
Why this source?
  • Describes the dismemberment of the massive Indo-Brahma river into the separate Indus and Ganga systems during the Pleistocene.
  • Identifies the Pleistocene upheaval in the western Himalayas and the uplift of the Potwar Plateau as the cause for creating the water divide between these systems.
  • Explains how geological shifts diverted major river systems that were previously connected or part of a single drainage.
Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 3: The Drainage System of India > SARASWATI-THE MYSTERY OF A LOST RIVER > p. 25
Presence: 3/5
“So the present day geomorphological set-up did not exist in 1500 B.C. and thus Indus, the Sutlej and the Beas followed independent courses to the sea. At present, more than 8000 years since the Vedas came into existence, some of the rivers mentioned therein have become defunct or have shifted from their original courses.• 3. Glaciological Evidence: According to the experts of glaciers and geomorphology, the Saraswati, Shatadru (Sutlej), and Yamuna derived their waters from the glaciers which had extensively covered the Himalayas during the Pleistocene Period. The Pleistocene is the first epoch of the Quaternary, preceded by the Pliocene and succeeded by the Holocene (from 1.64 million to 10,000 years ago).”
Why this source?
  • Notes that the Yamuna and the Shatadru (Sutlej) shared a common origin, deriving waters from the same Himalayan glaciers during the Pleistocene.
  • Highlights that these rivers have significantly shifted from their original courses since the Pleistocene and Vedic periods.
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