Tillite

Geography glossary

Topic: Continental Drift, Sea-floor Spreading and Plate Tectonics · NCERT: Class 11, Ch 4 "Distribution of Oceans and Continents"

Meaning

Tillite is a sedimentary rock (a rock made from layers of deposited material) formed when deposits left by glaciers harden. Finding tillite in a place shows that a thick ice sheet once covered it. The same tillite-bearing rock sequence is found on several southern continents, including some that are now warm or far apart. This shows they shared one long ice age while joined together, which is strong evidence for continental drift.

Example

Thick tillite lies at the base of the Gondwana system of rocks in peninsular India. The same sequence is found in Africa, the Falkland Islands, Madagascar, Antarctica and Australia. This shows that all these lands were once part of one southern landmass, Gondwanaland.

Don't confuse with

  • Placer deposits: Placers are loose deposits of heavy minerals such as gold, washed down by rivers. They support drift in a different way: Ghana's gold came from veins in Brazil. Tillite is glacier-made rock.

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