What do Twitter co-founders Jack Dorsey and Christopher "Biz" Stone have in common with Thomas Edison?

ENGADGET

But for the silly chaps, said Christopher Cockerell, we would still be living in the stone age.

ECONOMIST: Christopher Cockerell

Portland stone, mined in the south western county of Dorset, was used by Sir Christopher Wren to rebuild St Paul's Cathedral between 1675 and 1710.

BBC: Stone exhibit on a roll