The Shiwalik Hills: Young Mountains, Ancient Fossils

1.1 Where do the Shiwaliks sit, and how big are they?

The Shiwalik Hills are the southernmost range of the Himalayas. They are also the youngest of the three main Himalayan ranges.

• They stretch roughly 1,690 kilometres, from Kashmir through northern India into Nepal.
• They run parallel to the main Himalayan range, just south of it.
• They are also called the Outer Himalayas, or Manak Parbat in older texts.
• Elevations here usually range from 600 to 1,500 metres, much lower than the Greater Himalayas.
• The Greater Himalayas, by contrast, rise well above 6,000 metres, including several 8,000-metre peaks.
• In the east, the range gradually merges into the hills of Arunachal Pradesh.
• Different stretches carry local names, including the Jammu Hills in the west.

2.1 What are the Shiwaliks made of, and how did they form?

The hills consist of Tertiary sediments, unlike the older crystalline rock of the Greater Himalayas. These sediments were deposited roughly 16 to 5.2 million years ago.

• Rivers draining the rising Himalayas dumped sand, silt, and gravel into a foreland basin, which later got uplifted.
• Geologists call this sediment sequence the Siwalik Group, made mostly of sandstone, mudstone, and conglomerate.
• Sal forests and scrub vegetation typically cover these hills, adapted to their thin, rocky soil.
• Thin soil and steep slopes make the range prone to erosion, especially during heavy monsoon rain.
• Tectonic forces from the Indian plate’s collision with Asia continue to slowly uplift these hills today.
• The Main Boundary Thrust separates the Shiwaliks from the Lesser Himalayas to their north.
• These fault lines make the Shiwalik belt an active seismic zone, prone to periodic earthquakes.
• The Himalayan Frontal Thrust marks the Shiwaliks’ southern edge, against the plains.

3.1 What is a dun, and where’s the best-known one?

Longitudinal valleys called “duns” lie between the Shiwaliks and the Lesser Himalayas. Dehradun is the best-known example of a dun valley.

• Duns formed as rivers deposited sediment into a trough as the Shiwaliks rose.
• Kotli Dun and Patli Dun are other named dun valleys along the same range.
• Duns often have fertile alluvial soil, since rivers deposit fine sediment as they slow inside the valley.
• The term “doon” also survives directly in Dehradun’s own name.
• Because of that fertility, dun valleys support dense agricultural settlement, unlike the surrounding rocky hills.
• Dehradun itself has grown into a major city, and Uttarakhand’s capital, thanks partly to its dun setting.
• Rajaji Tiger Reserve sits within these Shiwalik foothills, protecting elephants and tigers near Dehradun and Haridwar.

4.1 What fossils have the Shiwaliks produced?

The Shiwaliks are famous for rich fossil beds of extinct apes and other primates.

• Fossil species found here include Ramapithecus punjabicus and Sivapithecus sivalensis.
• Fossils of ancient elephants, giraffes, and crocodiles have also been recovered from these rocks.
• The soft, sedimentary rock preserves fossils well and erodes easily, regularly exposing new ones.
• These beds are collectively known worldwide as the Siwalik fossil sequence, studied since the 1830s.
• British officers and geologists first documented major fossil finds here in the early-to-mid 19th century.
• Hugh Falconer and Proby Cautley were among the earliest scientists to catalogue Shiwalik fossils in detail.
• Many original Shiwalik fossils they collected are now held in museums in London and Kolkata.
• The Wadia Institute of Himalayan Geology, based in Dehradun, continues Shiwalik fossil research today.

5.1 What did researchers find in the Tatrot Formation?

In December 1992, researchers found what may be the world’s most ancient known early hominid fossil in the Shiwaliks’ Tatrot Formation.

• This pushed back the known timeline for early hominid-like primates in the region.
• The Tatrot Formation is one of several named rock layers within the Shiwalik sedimentary sequence.
• The Nagri, Dhok Pathan, and Pinjor Formations are other recognised layers within the same Shiwalik sequence.
• Each layer can be dated using its position and the fossils it contains, building a reliable timeline.

6.1 Why does this combination matter for exams?

One of the geologically youngest Himalayan ranges holds some of the oldest primate fossil evidence anywhere.