Hello Keith,
One other detail I forgot to mention is that pressure flakers are frequently held with a tilt, and not at a true "horizontal" angle. It would be what one author called a "wide slanting" angle.
That being said, if Catlin witnessed the flaker used in this manner, and he wrote that the "upper end of the flaker was struck", he would have been correct. The natural tilt of the flaker would cause the flaking end to be the upper end not the lower end.
When people read this, most probably assumed that the chisel was held as a normal stone chisel, and struck on the butt end. Actually, Catlin borrowed language that people were familiar with, in referring to the tools as a chisel, and a mallet. But, there is a difference in chiseling marble, or granite, and flaking flint. Normal stone chiseling involves pecking into the stone, or chipping off portions of the stone, whereas flintflaking involves peeing off long conchoidally made fractures from the surface of the stone. The way that the passage was interpreted (or misinterpreted) has more to do with a stone chiseling process, and not so much to do with flint flaking. Even when a pressure flaker is used, it takes more than pushing into an edge. On must both push in, and pull down, on the edge, to remove the flake.
Anyway, if the flaker was held as a pressure flaker is normally held, in Catlin's account, then the long end of the flaker, held against the platform, would have become the "upper end".
Also, the fact that everything is being held in hand, suggests that the rock was fairly brittle. When the hand is held as a rest, it is more frequently subject to movement. And, that detracts from flaking power. This process might have been used with pieces of obsidian that were already fairly thin.
