Thomas Jefferson is thought to have family links to slate quarrying

He was the third US president and one of 11 presidents and 17 signatories of the Declaration of Independence believed to have Welsh connections.

It is thought Jefferson - president between 1801-9 - had family links with the north Wales slate industry, although this is not proved.

The memorial will later be transferred to the Welsh Slate Museum in Llanberis.

Members from the group Welsh Across the World attended the unveiling - among them some of the two million Americans who claim Welsh ancestry.

"Many of them are descendents of families who set out for a new life from north Wales over 100 years ago," said Gwenllian Carr from the National Museum of Wales.

"And there still remain close links between the American slate industry and the one back home.

It is important to keep alive our historical links with the United States and the Jefferson memorial is a special way of doing this Dr Dafydd Roberts, Welsh Slate Museum

"There are quarries in upstate New York with names like 'Arvon' and 'Penrhyn.' "And though it can't be proved now, it's believed that Thomas Jefferson was from a slate-quarrying family."

The memorial has been made by the company Inigo Jones of Groeslon, near Caernarfon - itself a company that can trace its history back to the 1860s.

It will be transferred to the Welsh Slate Museum at Llanberis at the end of the 2005 National Eisteddfod, which is taking place at the Faenol estate in Gwynedd.

The keeper of the museum, Dr Dafydd Roberts, said the memorial does not just represent an historical link.

He added: "It is important to keep alive our historical links with the United States and the Jefferson memorial is a special way of doing this. "After all, we are also celebrating our contemporary connections."