Northern Pacific's Monad Symbol

Dennis DeBruler shared

When I shared Stephen Kellogg's photo I commented "The colors of the Ying-Yang are rather faded."

Mark Green commented "Terminology: Railroad "Ying-Yang" symbol is called a monad."

I'm posting this because I'm worried if months from now I'll be able to remember "monad."

(Update: Marty Bernard's notes on the Monad.)

Raymond Storey posted
Elkland Pa....The B&O
Dennis DeBruler The photo also captures one of the better images I have seen of Northern Pacific's Monad.
I'm trying to figure out how B&O got this far north in Pennsylvania.