I naturally assumed it was the second deal since it seems logical that with a little thought, someone could discover the ability to push over or down the top card and deal the second. But, to use the second, the glimpse or marked cards also had to be invented. So, it could be possible that the bottom deal came about because cheats could cull cards to the bottom when collecting them, then deal them out as needed. (Of course, one presumes the use of a false shuffle as well.) Finally, I found it interesting that Walter Scott's (The phantom at the card table) second deals were in part effective because everyone knew about and was watching for a bottom deal.
Which leads me to a research question. Can anyone cite the first published references to second dealing and bottom dealing, and does one predate the other?
Thanks cheating history buffs!