National Fossil Wood Park, Tiruvakkarai

The park at Tiruvakkarai holds about 200 fossil tree trunks lying on and just under the ground, ranging from 3 to 15 metres long and up to 5 metres around, all of them turned to stone. The logs have no branches or leaves, and they lie embedded in a pale rock called the Cuddalore Sandstone. Their wood was petrified about 20 million years ago, in the Miocene, which makes this a much younger petrified forest than the Cretaceous logs at Sathanur.

These trees did not grow where they now lie. A forest standing in place would leave stumps rooted upright, with branches and roots nearby. Instead the trunks are stripped bare and scattered, which tells geologists they were carried here. The likeliest story is a large flood that tore trees loose upstream, rolled them along, and dropped them together where the water slowed, burying them in river and coastal sand. That sand later hardened into the Cuddalore Sandstone.

Buried in porous sand, the wood met groundwater loaded with dissolved silica. Over a very long time the silica seeped into the trunks and replaced the wood cell by cell, hardening it into stone while copying the original structure. The copy is faithful enough that you can still count the growth rings and see the fine pits in the wood, which is how researchers can study trees that vanished 20 million years ago.

So two things had to line up for Tiruvakkarai to exist: sand porous enough to let silica-rich water move through, and enough time for that water to turn wood into rock. The flood delivered the trees and the burial protected them from rot; the groundwater did the slow work of preservation. A European naturalist, Pierre Sonnerat, described these stone logs as early as 1781, and today the Geological Survey of India protects the site as a National Geological Monument, a stretch of Miocene driftwood frozen in mid-journey.

A short reference note: this summary draws on third-party sources such as the Geological Survey of India and Wikipedia. In time I plan to give every geological feature its own learning-oriented write-up — with custom diagrams, graphs, and study pointers — as I’ve already done for the 11 locations that have an Instagram reel.

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