The yarn turned out to be chunky and hand spun, and really soft for something so old! It was made in Australia but we're still not completely sure what fibre it is. It is naturally dark brown, so feels too soft to be black sheep of some kind. My friend thought there might have been mention of alpacas.
It quickly earned the name Gorilla Sweater....every time I wear it I get the glorious but awful Mr Burns song in my head