A notable feature of Appalachian English is the a-prefix which occurs with participle forms ending in -ing. This prefix is pronounced as a schwa [ə]. The a-prefix most commonly occurs with progressives, in both past and non-past tenses. For example, "My cousin had a little pony and we was a-ridin' it one day"
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A-prefixing can be traced back to the 16th century: The construction reached its height from 1500-1700 and developed out of using the preposition "on" and a verbal noun ending in -ing. Only used in formal and educated writing in the 17th century, it became nonstandard in the 18th century. Montgomery (2009) argues that a-prefixing developed from the preposition "an"/"on" in Early Middle English and suggests that it arose from the loss of the -n from "on" in examples like "hee set before his eyes king Henrie the eight with all his Lordes on hunting in his forrest at Windsore" (Thomas Nashe, "Unfortunate Traveller," 1594).
An interesting tidbit from the Wikipedia page on Appalachian English: