19th-Century Carrier Cancels

Over the years, I've accumulated a good many covers with "carrier cancels" on the back, mostly as curiosities. The majority of them are to DC addresses and typically they are from the 1870s and '80s, although I have one from 1865. Most often the recipients seem to be lawyers or government offices.

I don't know much about these, but I'd like to learn more. Can any forum member provide some insight or direct me to a good reference? I'm interested in how the post office decided a letter merited carrier delivery -- there doesn't appear to be any extra charge for this. And why do these backstamps disappear after the 1880s?

Greg, from what I understand, these carrier postmarks are unrelated to the private carrier services of earlier years. These postmarks were stamped when the carrier received the mail. I assume the practice faded away because of the greater volume of mail and its not really having a vital use.

Yep, I know they are post office markings, not private. I'm trying to figure out what kind of mail got this special service. And now that I think of it, Special Delivery service started in 1885 -- maybe that's what supplanted this kind of carrier delivery.

Greg, from what little I've read--admittedly--I don't think the postmark signifies any special service.