Strange green swirlly plastic like rock?

[Togalosh]

I'm shocked by all this as our allotment was probably part of the Chamberlain estate orchards & was a farm before that..but I have to concede that it could be plausible that industrial waste from further afield was brought in to make a path/road through it...it all adds to the history of the place..it just looks too nice to be slag.

Oddly enough all along the small rivers around here & only a few hundred yards away they've found prehistoric burnt stones found nowhere else.


Thanks for the help.