I just realized I put a closeup of this on Page 7 of this thread.
Here's an early Railroad postmark with a 3d stamp.
KINGS. & TORONTO GR. TRK R. WAY P.O. No. 2
C UP AUG 27 1857
No. 2 was the postmark device number and UP being the direction the train was travelling, in this case, West. The back has two scarce postmarks, both faint, a large circular transit postmark from LONDON and an early double arc PORT SARNIA receiver.

