Jefferson and Lewis had talked at length about these tribes, on the basis of near-complete ignorance. They speculated that the lost tribe of Israel could be out there on the Plains, but it was more likely, in their minds, that the Mandans were a wandering tribe of Welshmen.2 Because they subscribed to such odd ideas, Jefferson’s instructions to Lewis on how to deal with the tribes were, in most particulars, hopelessly naive and impossible to carry out.
