i doubt that this stuff would knap well, there's too many inclusions, holes, etc to make it fracture well. there's a couple partial fractures on a piece or two, and you can see that it's not an even, smooth, "clamshell" like fracture.
hmm, if only the local historical society wasn't "closed for the season"...
griz, i'm looking forward to seeing pics of the stuff you found.
tmm