Most mysterious English lake with a bed of stone (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of E (‘English’) plus ERIE (‘lake with a bed’ – the ‘bed’ is a useless piece of information – what lake does not have a bed? – but I think it must belong here) plus ST (‘stone’). Better: ‘bed’ just affirms the order of the particles (in a down light).