In 1923 the petrologist Herbert Henry Thomas proposed that bluestone from the hills corresponded to that used to build the inner circle of Stonehenge, and later geologists suggested that Carn Menyn (formerly called Carn Meini) was one of the bluestone sources. Recent geological work has shown this theory to be incorrect. It is now thought that the bluestones at Stonehenge and fragments of bluestone found in the Stonehenge "debitage" have come from multiple sources on the northern flanks of the hills, such as at Craig Rhos-y-felin. Advanced details of a recent contribution to the puzzle of the precise origin of the Stonehenge bluestones were published by the BBC in November 2013.