Where are the oldest rails to be found on IR?

Most of the very old tracks have by now been relaid and renovated, so that it is very hard to find very old rails. Good bets are the meter-gauge and narrow-gauge lines that don't see much traffic. Abandoned lines (such as at the Bombay Port Trust railway) also sometimes have very old rails left intact. The Bombay Port Trust railway tracks between Dockyard Road and Wadala / Raoli might be among the oldest. Bullhead rails from the late 19th century or early 20th century were still to be found in some areas (e.g. peripheral sidings at Dadar, near Thane, etc.) but many have by now been replaced.

Source - IFRCA.org