Grand Am

There has been long suspicion that the variant use of "am" in Black English is a minstrel show fabrication that was never actually used.  "Brother Jones am a fine preacher," or "The corn harvest am a little late this year."

Scholars of AAVE have typically assumed that the invariant am typical of minstrel depictions of black speech was a fabrication, used neither by modern nor earlier black Americans. However, the frequency with which invariant am occurs in transcriptions of ex-slave speech has always lent a certain uncertainty here, despite claims that these must have been distortions introduced by the transcribers. 

John McWhorter uncovers enough believable, non-critical and nonsatiric reports of the usage to declare it was not only used in Southern Black dialect in the 1800s, but that it came from nonstandard dialects in England in the late 1700s, which were still in occasional use up until the early 1900s. The 20-min podcast am here.