manicmike

That's extremely cool Steve! If you're lucky it won't be cotton but silk.
You'll certainly find out as soon as you start unravelling (it takes almost no pressure to break 100+ year old cotton). If you want to be certain, burn a little: Burning cotton smells like you're ironing your t-shirt, silk smells like hair.
They don't look black: Is this just the photograph or have they faded to a greeny brown?
Regardless, it's a rare find, and I for one am keen to know more.
The Merrick Thread Co. seem to have been decades ahead of their time. I just Googled them and there's a few interesting hits.