Yep Tom, ain't nothing better than what you can find in your own backyard!
Those are nice! I have an agate-nut friend who gets out to Missouri
once in a while to hunt for rocks and I believe I've heard him talk about those type
and how hard they are to find anymore.
I think those are probably something you would want to collect
as many as you can of. I think they are pretty valuable to agate collectors
and would definitely be good trading material.
I've got company in town for the next few days but will try and
see what else I can find out about them.
Can't answer your question about the "birdsnest" material
but look forward to hearing/finding an answer.
Real nice find and thanks for sharing!
Joe