In what kind of container is Ebenezer Dorset instructed to put the ransom in "The Ransom of Red Chief"?

Ebenezer Dorset is instructed to place the ransom money, along with his reply to the letter, in a pasteboard box.
In their letter to the wealthy banker Dorset, Sam writes that they are "two desperate men" who will return the boy safely if Mr. Dorset places fifteen hundred dollars in large bills in the same place as his reply to their message:

At the bottom of the fence-post, opposite the third tree, will be found a small pasteboard box.

The original idea by the two kidnappers was to take the child of a prominent citizen of the small community of Summit, Alabama, where the enforcer of the law would only be a constable. After they capture the red-headed boy, it is Sam and especially Bill who become the victims because the child, who wishes to be called Red Chief, is wild and dangerous. For instance, he sits on top of Bill and tries to scalp him with a case-knife, and he threatens to burn Sam at the stake. Later, he rides Bill all around the area in which they are hiding, then slings a rock at him as though re-enacting the story of David and Goliath.
Desperate and frightened, Bill suggests that he and Sam lower the ransom from $2000 to $1500. They receive a reply from Mr. Dorset, who states that he will take the boy back only if they pay him. The two men comply and return Red Chief to his father, handing him $250 instead of receiving $1500.