Step 1: Identify the Volcanic Regions.
- The Deccan Traps are one of the largest volcanic provinces in the world, but they are younger than the Panjal volcanics.
- The Panjal volcanics are considered among the oldest in India, formed during the late Palaeozoic and early Mesozoic era.
- Sylhet and Rajmahal are also volcanic formations but are younger than the Panjal volcanics.
Step 2: Conclusion.
Thus, the oldest volcanics are found in the Panjal region.
Final Answer:
\[
\boxed{\text{Panjal}}
\]