Spirit Tracks Ferrus Letter #3

[Mrflamexd3]

Okay so I obtained and finished Ferrus Letter #2 (and got the Force Gem). Now I only need one more letter which is the 3rd letter from Ferrus, and i'm a little stumped...how exactly do I get the letter?

 

[Shadsie]

If I remember, he should be in the forest area, the "lost woods" area... it's been a bit since I've played the game, but you've already taken him to the underwater temple, right? He should have a gift to thank you with if you drive your train through the woods outside of Whittleton... at least that's how I remember it.

It could be that you have to do something first. I remember letters being events-based.