In the mid-1700s, when the M-D Line was being surveyed, what we know as the blues was still evolving from minuets, round singing, madrigals, and operatic arias. By the early 1800s, however, what was then called "the violets" (a precursor of the blues) was already demonstrating to musicologists what its future would be -- heavy metal rap music (I didn't say that it was a viable line, just a precursor). After Mogan David and Manischewitz windes became popular in the early 1900s, the blues took on its own life because it was now possible to truly feel the line, "Woke up this mornin' with my...."

And that, by the way, is why it's known as the M-D Line. Yankees couldn't abide calling it the "Mogan David Line", and called it the "Mason-Dixon Line" instead.

The original surveyors were two guys name William Roque and Harold Ireland, but there were copyright lawsuits about the use of the name "Roque-Ireland Line."