I've actually seen a comparison to an American Indian language to the Basque language. (forgot which tribe/language) A number of unexplainable similarities were found. Now, Plutarch, examining the ruins of Carthage cites charts/graphs/etc. he found that were accounts of trade with nations across the Atlantic Ocean.
I once read a reference to an expedition in the late 1600s wherein a welshman was able to communicate with a group of Noth American Indians in his native speech. I've never been able to find out more about it, but I found that to be fascinating.
It's already been conclusively proved that the Norse were in N.A. 500 years before Columbus. We will probably eventually learn that there was a great deal more contact between the "Old" and "New" Worlds than we ever imagined.
Some scholars believe Basque is actually related to the languages spoken by the early Cro-Magnon invaders of Europe.
Basque isn't the only linguistic anomaly in Europe. There is also Pictish, the language spoken by the early inhabitants of Scotland, Elymian - a language spoken in western ancient Sicily, Etruscan, a whole group of languages spoken in the Alpine area in ancient times, the ancient Iberian language of southern Spain, and ancient Minoan (Pre-Linear B which was actually an ancient form of Greek)>