RAS question
The Shivalik Range (Outer Himalayas) is composed primarily of which type of deposits?
Correct answer: (D) Unconsolidated sediments (sand, gravel, conglomerate).
The Shivalik Range, or Outer Himalayas, is composed primarily of unconsolidated river sediments such as sand, gravel and conglomerate.
Explanation
The Shivalik Range is the outermost and youngest Himalayan range, and its material points to recent river deposition rather than hard crystalline or volcanic rock. It is made mainly of unconsolidated sediments: sand, gravel and conglomerates. NCERT's discussion of the Shiwalik supports this sedimentary reading by referring to its alluvial deposits, including sands, silt, clay, boulders and conglomerates. Unconsolidated river sediments fit the geology of the Outer Himalayas. The associated dun valleys, such as Dehradun, lie between the Shivalik and the Middle Himalayas, reinforcing the youngest, outer Himalayan belt's depositional origin.
Why the other options are wrong
- (A) Igneous and volcanic rocks are not the Shivalik's primary unconsolidated alluvial and river-borne sediments.
- (B) Ancient crystalline granites imply an old, hard crystalline basement, whereas the Shivalik is the youngest Himalayan range made of loose sedimentary deposits.
- (C) Metamorphic rocks such as gneiss and schist are not the primary Shivalik material; the relevant deposits are sand, gravel, boulders and conglomerates.
Concept
Himalayan physiography distinguishes the youngest Outer Himalayas from the older inner ranges. Rock type, relief and depositional features help separate the major Himalayan divisions in RAS geography.