What's this beneath my wallpaper?

[HenryBukowski]

Hi there,

Today I embarked upon stripping wallpaper in my living room. However I've got tripped up by not knowing what this layer underneath is. It's like a cardboard type surface. I don't think it's part of the wallpaper, but its got follows the same border lines as each bit of wallpaper. In most places it's completely smooth except in one or two places where it's come away slightly to reveal a grey material beneath.

My question is simply, does anyone know what this cardboardy layer is? And should I be removing this before painting over?

Much appreciated everyone.
Henry

 

[motorbiking]

Lining paper and the grey stuff underneath is your plaster which if its a 1960s +-10yr build could be seraphite.