A double dash usage

This hideous murder accomplished, I set myself forthwith, and with entire deliberation, to the task of concealing the body. I knew that I could not remove it from the house, either by day or by night, without the risk of being observed by the neighbors. Many projects entered my mind. At one period I thought of cutting the corpse into minute fragments, and destroying them by fire. At another, I resolved to dig a grave for it in the floor of the cellar. Again, I deliberated about casting it in the well in the yard -- about packing it in a box, as if merchandize, with the usual arrangements, and so getting a porter to take it from the house.
by Edgar Allan Poe http://poestories.com/read/blackcat>

I'd like to know whether the double dash before "about packing" plays the role the like of a comma or "and."

Thank you in advance for your help.