Drove 3 hours away to Kingston today to take my daughter back to university. After having lunch we wandered a nearby flea market to help us digest. I found this cover, which I actually passed by, but came back to, and got very cheaply.
The stamp itself isn't in very good shape, which is why I walked away initially. It's faded and difficult to identify. The gray blue colour tells me it may be a
#156 or 182, but the secret mark is very faint. But it was the cancel that caught my eye. A nice big simple CHICAGO.


It wasn't until I got it home I realized it was a package sent between ticket agents in Chicago and St. Lambert Quebec for, I believe, the Grand Trunk Railroad.
Any thoughts on the cancel and cover?
edit -
a closer look leads me to believe the stamp is an SC#206 (shading in the arabesques on the upper part of the stamp).