Pronunciation of Argyll

[OC Richard]

The New England replacement of the letter "R" with the letter "H" (I pahk my cah)

Actually the reason is because those areas were originally settled by people from places in England where final "r" had never been pronounced. Some of those people also settled in the South, which is why some Southern accents likewise have no final "r". (Most of southeastern England was non-rhotic, and these people brought their non-rhotic speech to the colonies. Southwest England, on the other hand, had accents with strong final "r" and it was these people who brought the rhotic speech to the colonies.)

Here's the accent from southwestern England, the "west country accent", where you can clearly hear the strong final "r". It's worth a listen! Because most of the time the English accents we're exposed to are the non-r ones.
http://www.youtube.com/watch?v=ruCG8HGRKR0&feature=fvst

Here's the Wikipedia article which describes the division in English all over the world between rhotic and non-rhotic speech

http://en.wikipedia.org/wiki/Rhotic_...rhotic_accents

If you're interested in all this stuff I highly recommed the book Albion's Seed: Four British Folkways in America by David Hackett Fischer in which he traces regional US accents, food styles, approaches to family, religion, etc etc back to four mass migrations from various parts of Britain to various parts of the USA in the 17th century.