The Lead Mines of Marrick, Swaledale

In researching into the Lead Mines of Marrick, I have found and bought a book by the northern mine research society called British Mining No.38 a history of the manor and lead mines of Marrick, Swaledale by L.O Tyson. In this book there is some interesting information on the history of this mine it is mentioned that there is a tradition that Hurst was once a Roman penal colony, using slaves to mine for the Lead. This was first reported about by a H.Speight in his book Romantic Richmondshire 1897, it states of the finding of a Lead Pig stamped with the name of Hadrian, Roman Emperor. The Pig was supposed to be in the British Museum but in 1940's it could not be traced and located.